reptile
Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...
s of the
clade
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
Dinosauria. They first appeared during the
Triassic
The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
period
Period may refer to:
Common uses
* Era, a length or span of time
* Full stop (or period), a punctuation mark
Arts, entertainment, and media
* Period (music), a concept in musical composition
* Periodic sentence (or rhetorical period), a concept ...
, between 243 and 233.23
million years ago
The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds.
Usage
Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago). ...
(mya), although the exact origin and timing of the
evolution of dinosaurs
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
is the subject of active research. They became the dominant terrestrial
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
s after the
Triassic–Jurassic extinction event
The Triassic–Jurassic (Tr-J) extinction event, often called the end-Triassic extinction, marks the boundary between the Triassic and Jurassic periods, , and is one of the top five major extinction events of the Phanerozoic eon, profoundly affect ...
201.3 mya; their dominance continued throughout the
Jurassic
The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
and
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
periods. The
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
record shows that
bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
s are
feathered dinosaur
A feathered dinosaur is any species of dinosaur possessing feathers. While this includes all species of birds, there is a hypothesis that many, if not all non-avian dinosaur species also possessed feathers in some shape or form.
It has been su ...
theropods
Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...
during the
Late Jurassic
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987.
In European lithostratigraphy, the name ...
epoch, and are the only dinosaur lineage known to have survived the
Cretaceous–Paleogene extinction event
The Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary extinction) was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. With the ...
approximately 66 mya. Dinosaurs can therefore be divided into avian dinosaurs—birds—and the extinct non-avian dinosaurs, which are all dinosaurs other than birds.
Dinosaurs are varied from
taxonomic
Taxonomy is the practice and science of categorization or classification.
A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...
ecological
Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps wi ...
standpoints. Birds, at over 10,700 living
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
, are among the most diverse group of vertebrates. Using fossil evidence,
paleontologists
Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
have identified over 900 distinct
genera
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...
and more than 1,000 different species of non-avian dinosaurs. Dinosaurs are represented on every continent by both
extant
Extant is the opposite of the word extinct. It may refer to:
* Extant hereditary titles
* Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English
* Extant taxon, a taxon which is not extinct, ...
species (birds) and fossil remains. Through the first half of the 20th century, before birds were recognized as dinosaurs, most of the scientific community believed dinosaurs to have been sluggish and cold-blooded. Most research conducted since the 1970s, however, has indicated that dinosaurs were active animals with elevated
metabolism
Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
s and numerous adaptations for social interaction. Some were
herbivorous
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
, others
carnivorous
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other sof ...
. Evidence suggests that all dinosaurs were
egg-laying
Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), and ...
, and that
nest
A nest is a structure built for certain animals to hold eggs or young. Although nests are most closely associated with birds, members of all classes of vertebrates and some invertebrates construct nests. They may be composed of organic materia ...
-building was a trait shared by many dinosaurs, both avian and non-avian.
While dinosaurs were ancestrally
bipedal
Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' ...
, many
extinct
Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
groups included
quadrupedal
Quadrupedalism is a form of locomotion where four limbs are used to bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four limbs is said to be a quadruped (from Latin ''quattuor' ...
species, and some were able to shift between these stances. Elaborate display structures such as horns or crests are common to all dinosaur groups, and some extinct groups developed
skeletal
A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...
modifications such as bony armor and spines. While the dinosaurs' modern-day surviving avian lineage (birds) are generally small due to the constraints of flight, many prehistoric dinosaurs (non-avian and avian) were large-bodied—the largest
sauropod
Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their bo ...
dinosaurs are estimated to have reached lengths of and heights of and were the largest land animals of all time. The misconception that non-avian dinosaurs were uniformly gigantic is based in part on
preservation bias
Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Efremov t ...
, as large, sturdy
bone
A bone is a Stiffness, rigid Organ (biology), organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red blood cell, red and white blood cells, store minerals, provid ...
s are more likely to last until they are fossilized. Many dinosaurs were quite small, some measuring about in length.
The first dinosaur fossils were recognized in the early 19th century, with the name "dinosaur" (meaning "terrible lizard") being coined by Sir
Richard Owen
Sir Richard Owen (20 July 1804 – 18 December 1892) was an English biologist, comparative anatomist and paleontologist. Owen is generally considered to have been an outstanding naturalist with a remarkable gift for interpreting fossils.
Owe ...
in 1841 to refer to these "great fossil lizards". Since then, mounted fossil dinosaur skeletons have been major attractions at museums worldwide, and dinosaurs have become an enduring part of popular culture. The large sizes of some dinosaurs, as well as their seemingly monstrous and fantastic nature, have ensured their regular appearance in best-selling books and films, such as ''
Jurassic Park
''Jurassic Park'', later also referred to as ''Jurassic World'', is an American science fiction media franchise created by Michael Crichton and centered on a disastrous attempt to create a theme park of cloned dinosaurs. It began in 1990 when ...
''. Persistent public enthusiasm for the animals has resulted in significant funding for dinosaur science, and new discoveries are regularly covered by the media.
Definition
Under
phylogenetic nomenclature
Phylogenetic nomenclature is a method of nomenclature for taxa in biology that uses phylogenetic definitions for taxon names as explained below. This contrasts with the traditional approach, in which taxon names are defined by a '' type'', which ...
, dinosaurs are usually defined as the group consisting of the
most recent common ancestor
In biology and genetic genealogy, the most recent common ancestor (MRCA), also known as the last common ancestor (LCA) or concestor, of a set of organisms is the most recent individual from which all the organisms of the set are descended. The ...
(MRCA) of ''
Triceratops
''Triceratops'' ( ; ) is a genus of herbivore, herbivorous Chasmosaurinae, chasmosaurine Ceratopsidae, ceratopsid dinosaur that first appeared during the late Maastrichtian stage of the Late Cretaceous Period (geology), period, about 68 m ...
'' and
modern birds
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight s ...
(Neornithes), and all its descendants. It has also been suggested that Dinosauria be defined with respect to the MRCA of ''
Megalosaurus
''Megalosaurus'' (meaning "great lizard", from Greek , ', meaning 'big', 'tall' or 'great' and , ', meaning 'lizard') is an extinct genus of large carnivorous theropod dinosaurs of the Middle Jurassic period (Bathonian stage, 166 million years a ...
'' and ''
Iguanodon
''Iguanodon'' ( ; meaning 'iguana-tooth'), named in 1825, is a genus of iguanodontian dinosaur. While many species have been classified in the genus ''Iguanodon'', dating from the late Jurassic Period to the early Cretaceous Period of Asia, Eu ...
'', because these were two of the three genera cited by
Richard Owen
Sir Richard Owen (20 July 1804 – 18 December 1892) was an English biologist, comparative anatomist and paleontologist. Owen is generally considered to have been an outstanding naturalist with a remarkable gift for interpreting fossils.
Owe ...
when he recognized the Dinosauria. Both definitions result in the same set of animals being defined as dinosaurs: "Dinosauria =
Ornithischia
Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek s ...
+
Saurischia
Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...
". This definition includes major groups such as
ankylosauria
Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. ...
ns (armored herbivorous quadrupeds),
stegosauria
Stegosauria is a group of herbivorous ornithischian dinosaurs that lived during the Jurassic and early Cretaceous periods. Stegosaurian fossils have been found mostly in the Northern Hemisphere, predominantly in what is now North America, Europe, ...
ns (plated herbivorous quadrupeds),
ceratopsia
Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. ...
ns (bipedal or quadrupedal herbivores with
neck frill
A neck frill is the relatively extensive margin seen on the back of the heads of reptiles with either a bony support such as those present on the skulls of dinosaurs of the suborder Marginocephalia or a cartilaginous one as in the frill-necked ...
s),
pachycephalosauria
Pachycephalosauria (; from Greek παχυκεφαλόσαυρος for 'thick headed lizards') is a clade of ornithischian dinosaurs. Along with Ceratopsia, it makes up the clade Marginocephalia. With the exception of two species, most pachycephal ...
ns (bipedal herbivores with thick skulls),
ornithopod
Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (), that started out as small, bipedal running grazers and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world ...
s (bipedal or quadrupedal herbivores including " duck-bills"),
theropod
Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...
s (mostly bipedal carnivores and birds), and
sauropodomorphs
Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lon ...
(mostly large herbivorous quadrupeds with long necks and tails).
Birds are now recognized as being the sole surviving lineage of theropod dinosaurs. In traditional
taxonomy
Taxonomy is the practice and science of categorization or classification.
A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...
, birds were considered a separate
class
Class or The Class may refer to:
Common uses not otherwise categorized
* Class (biology), a taxonomic rank
* Class (knowledge representation), a collection of individuals or objects
* Class (philosophy), an analytical concept used differentl ...
that had evolved from dinosaurs, a distinct
superorder
Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
. However, a majority of contemporary paleontologists concerned with dinosaurs reject the traditional style of classification in favor of
phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
taxonomy; this approach requires that, for a group to be natural, all descendants of members of the group must be included in the group as well. Birds are thus considered to be dinosaurs and dinosaurs are, therefore, not extinct. Birds are classified as belonging to the subgroup
Maniraptora
Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to ''Ornithomimus velox''. It contains the major subgroups Avialae, Deinonychosauria, Oviraptoros ...
, which are
coelurosaurs
Coelurosauria (; from Greek, meaning "hollow tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs.
Coelurosauria is a subgroup of theropod dinosaurs that includes compsognathids, tyrann ...
, which are theropods, which are saurischians, which are dinosaurs.
Research by Matthew G. Baron,
David B. Norman
David Bruce Norman (born 20 June 1952 in the United Kingdom) is a British paleontologist, currently the main curator of vertebrate paleontology at the Sedgwick Museum, Cambridge University. From 1991 to 2011, Norman has also been the Sedgwick Mus ...
, and Paul M. Barrett in 2017 suggested a radical revision of dinosaurian systematics. Phylogenetic analysis by Baron ''et al.'' recovered the Ornithischia as being closer to the Theropoda than the Sauropodomorpha, as opposed to the traditional union of theropods with sauropodomorphs. They resurrected the clade
Ornithoscelida
Ornithoscelida () is a proposed clade that includes various major groupings of dinosaurs. An order Ornithoscelida was originally proposed by Thomas Henry Huxley but later abandoned in favor of Harry Govier Seeley's division of Dinosauria into Sau ...
to refer to the group containing Ornithischia and Theropoda. Dinosauria itself was re-defined as the last common ancestor of ''Triceratops horridus'', ''
Passer domesticus
The house sparrow (''Passer domesticus'') is a bird of the sparrow family Passeridae, found in most parts of the world. It is a small bird that has a typical length of and a mass of . Females and young birds are coloured pale brown and grey, an ...
'' and ''
Diplodocus carnegii
''Diplodocus'' (, , or ) was a genus of diplodocid sauropod dinosaurs, whose fossils were first discovered in 1877 by S. W. Williston. The generic name, coined by Othniel Charles Marsh in 1878, is a neo-Latin term derived from Greek διπλ ...
'', and all of its descendants, to ensure that sauropods and kin remain included as dinosaurs. "A version of this article appears in print on March 28, 2017, on Page D6 of the New York edition with the headline: Shaking Up the Dinosaur Family Tree." "This file contains Supplementary Text and Data, Supplementary Tables 1-3 and additional references." Supplementary Information /ref>
General description
Using one of the above definitions, dinosaurs can be generally described as
archosaur
Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian d ...
pterosaur
Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 to ...
s,
mosasaur
Mosasaurs (from Latin ''Mosa'' meaning the 'Meuse', and Greek ' meaning 'lizard') comprise a group of extinct, large marine reptiles from the Late Cretaceous. Their first fossil remains were discovered in a limestone quarry at Maastricht on th ...
s,
ichthyosaur
Ichthyosaurs (Ancient Greek for "fish lizard" – and ) are large extinct marine reptiles. Ichthyosaurs belong to the order known as Ichthyosauria or Ichthyopterygia ('fish flippers' – a designation introduced by Sir Richard Owen in 1842, altho ...
s,
plesiosaurs
The Plesiosauria (; Greek: πλησίος, ''plesios'', meaning "near to" and ''sauros'', meaning "lizard") or plesiosaurs are an order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia.
Plesiosaurs first appeared ...
, and ''
Dimetrodon
''Dimetrodon'' ( or ,) meaning "two measures of teeth,” is an extinct genus of non-mammalian synapsid that lived during the Cisuralian (Early Permian), around 295–272 million years ago (Mya). It is a member of the family Sphenacodontid ...
'', while often popularly conceived of as dinosaurs, are not taxonomically classified as dinosaurs. Pterosaurs are distantly related to dinosaurs, being members of the clade
Ornithodira
Avemetatarsalia (meaning "bird metatarsals") is a clade of diapsid reptiles containing all archosaurs more closely related to birds than to crocodilians. The two most successful groups of avemetatarsalians were the dinosaurs and pterosaurs. Dinos ...
. The other groups mentioned are, like dinosaurs and pterosaurs, members of
Sauropsida
Sauropsida ("lizard faces") is a clade of amniotes, broadly equivalent to the class Reptilia. Sauropsida is the sister taxon to Synapsida, the other clade of amniotes which includes mammals as its only modern representatives. Although early syna ...
(the reptile and bird clade), except ''Dimetrodon'' (which is a
synapsid
Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes reptil ...
). None of them had the erect hind limb posture characteristic of true dinosaurs.
Dinosaurs were the dominant terrestrial vertebrates of the
Mesozoic
The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...
Era
An era is a span of time defined for the purposes of chronology or historiography, as in the regnal eras in the history of a given monarchy, a calendar era used for a given calendar, or the geological eras defined for the history of Earth.
Comp ...
, especially the Jurassic and Cretaceous periods. Other groups of animals were restricted in size and niches;
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s, for example, rarely exceeded the size of a domestic cat, and were generally rodent-sized carnivores of small prey. They have always been recognized as an extremely varied group of animals; over 900 non-avian dinosaur genera have been identified with certainty as of 2018, and the total number of genera preserved in the fossil record has been estimated at around 1850, nearly 75% of which remain to be discovered, and 1124 species by 2016. A 1995 study predicted that about 3,400 dinosaur genera ever existed, including many that would not have been preserved in the fossil record.
In 2016, the estimated number of dinosaur species that existed in the Mesozoic was 1,543–2,468. In 2021, the number of modern-day birds (avian dinosaurs) was estimated to be at 10,806 species. Some are herbivorous, others carnivorous, including seed-eaters, fish-eaters, insectivores, and omnivores. While dinosaurs were ancestrally bipedal (as are all modern birds), some prehistoric species were quadrupeds, and others, such as ''
Anchisaurus
''Anchisaurus'' is a genus of basal sauropodomorph dinosaur. It lived during the Early Jurassic Period, and its fossils have been found in the red sandstone of the Portland Formation, Northeastern United States, which was deposited from the Het ...
'' and ''Iguanodon'', could walk just as easily on two or four legs. Cranial modifications like horns and crests are common dinosaurian traits, and some extinct species had bony armor. Although known for large size, many Mesozoic dinosaurs were human-sized or smaller, and modern birds are generally small in size. Dinosaurs today inhabit every continent, and fossils show that they had achieved global distribution by at least the
Early Jurassic
The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-J ...
epoch. Modern birds inhabit most available habitats, from terrestrial to marine, and there is evidence that some non-avian dinosaurs (such as ''
Microraptor
''Microraptor'' (Greek, μικρός, ''mīkros'': "small"; Latin, ''raptor'': "one who seizes") is a genus of small, four-winged dromaeosaurid dinosaurs. Numerous well-preserved fossil specimens have been recovered from Liaoning, China. They dat ...
'') could fly or at least glide, and others, such as
spinosaurids
The Spinosauridae (or spinosaurids) are a clade or Family (taxonomy), family of tetanuran theropod dinosaurs comprising ten to seventeen known genera. They came into prominence during the Cretaceous Geological period, period. Spinosaurid fossils h ...
, had
semiaquatic
In biology, semiaquatic can refer to various types of animals that spend part of their time in water, or plants that naturally grow partially submerged in water. Examples are given below.
Semiaquatic animals
Semiaquatic animals include:
* Verte ...
habits.
Distinguishing anatomical features
While recent discoveries have made it more difficult to present a universally agreed-upon list of their distinguishing features, nearly all dinosaurs discovered so far share certain modifications to the ancestral archosaurian skeleton, or are clearly descendants of older dinosaurs showing these modifications. Although some later groups of dinosaurs featured further modified versions of these traits, they are considered typical for Dinosauria; the earliest dinosaurs had them and passed them on to their descendants. Such modifications, originating in the most recent common ancestor of a certain taxonomic group, are called the
synapomorphies
In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...
of such a group.
A detailed assessment of archosaur interrelations by
Sterling Nesbitt
Sterling Nesbitt (born March 25, 1982, in Mesa, Arizona) is an American paleontologist best known for his work on the origin and early evolutionary patterns of archosaurs. He is currently an associate professor at Virginia Tech in the Department of ...
confirmed or found the following twelve unambiguous synapomorphies, some previously known:
* In the
skull
The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...
, a supratemporal fossa (excavation) is present in front of the
supratemporal fenestra
The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...
, the main opening in the rear skull roof
*
Epipophyses
Epipophyses are bony projections of the cervical vertebrae found in archosauromorphs, particularly dinosaurs (including some basal birds). These paired processes sit above the postzygapophyses on the rear of the vertebral neural arch. Their morp ...
, obliquely backward-pointing processes on the rear top corners of the anterior (front) neck
vertebra
The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
e behind the
atlas
An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth.
Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geographic ...
and
axis
An axis (plural ''axes'') is an imaginary line around which an object rotates or is symmetrical. Axis may also refer to:
Mathematics
* Axis of rotation: see rotation around a fixed axis
*Axis (mathematics), a designator for a Cartesian-coordinate ...
, the first two neck vertebrae
* Apex of a deltopectoral crest (a projection on which the deltopectoral muscles attach) located at or more than 30% down the length of the
humerus
The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...
(upper arm bone)
*
Radius
In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...
, a lower arm bone, shorter than 80% of humerus length
*
Fourth trochanter
The fourth trochanter is a shared characteristic common to archosaurs. It is a knob-like feature on the posterior-medial side of the middle of the femur shaft that serves as a muscle attachment, mainly for the ''musculus caudofemoralis longus'', ...
(projection where the
caudofemoralis The caudofemoralis (from the Latin ''cauda'', tail and ''femur'', thighbone) is a muscle found in the pelvic limb of mostly all animals possessing a tail. It is thus found in nearly all tetrapods.
Location
The caudofemoralis spans plesiomorphi ...
muscle attaches on the inner rear shaft) on the
femur
The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...
(thigh bone) is a sharp flange
* Fourth trochanter asymmetrical, with distal, lower, margin forming a steeper angle to the shaft
* On the
astragalus
''Astragalus'' is a large genus of over 3,000 species of herbs and small shrubs, belonging to the legume family Fabaceae and the subfamily Faboideae. It is the largest genus of plants in terms of described species. The genus is native to tempe ...
and
calcaneum
In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel) or heel bone is a bone of the tarsus of the foot which constitutes the heel. In some other animals, it is the point of the hock.
St ...
, upper ankle bones, the proximal articular facet, the top connecting surface, for the
fibula
The fibula or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity is ...
occupies less than 30% of the transverse width of the element
* Exoccipitals (bones at the back of the skull) do not meet along the midline on the floor of the endocranial cavity, the inner space of the braincase
* In the pelvis, the proximal articular surfaces of the
with the ilium and the pubis are separated by a large concave surface (on the upper side of the ischium a part of the open hip joint is located between the contacts with the pubic bone and the ilium)
*
Cnemial crest The cnemial crest is a crestlike prominence located at the front side of the head of the tibiotarsus or tibia in the legs of many mammals and reptiles (including birds and other dinosaurs). The main extensor muscle of the thigh
In human anatomy ...
on the
tibia
The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...
(protruding part of the top surface of the shinbone) arcs anterolaterally (curves to the front and the outer side)
* Distinct proximodistally oriented (vertical) ridge present on the posterior face of the distal end of the tibia (the rear surface of the lower end of the shinbone)
* Concave articular surface for the fibula of the calcaneum (the top surface of the calcaneum, where it touches the fibula, has a hollow profile)
Nesbitt found a number of further potential synapomorphies and discounted a number of synapomorphies previously suggested. Some of these are also present in
silesaurids
Silesauridae is an extinct family of Triassic dinosauriforms. It is most commonly considered to be a clade of non-dinosaur dinosauriforms, and the sister group of dinosaurs. Some studies have instead suggested that most or all silesaurids compri ...
, which Nesbitt recovered as a sister group to Dinosauria, including a large anterior trochanter, metatarsals II and IV of subequal length, reduced contact between ischium and pubis, the presence of a cnemial crest on the tibia and of an ascending process on the astragalus, and many others.
A variety of other skeletal features are shared by dinosaurs. However, because they are either common to other groups of archosaurs or were not present in all early dinosaurs, these features are not considered to be synapomorphies. For example, as
diapsid
Diapsids ("two arches") are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The group first appeared about three hundred million years ago ...
s, dinosaurs ancestrally had two pairs of
Infratemporal fenestra
An infratemporal fenestra, also called the lateral temporal fenestra or simply temporal fenestra, is an opening in the skull behind the orbit in some animals. It is ventrally bordered by a zygomatic arch. An opening in front of the eye sockets, ...
e (openings in the skull behind the eyes), and as members of the diapsid group Archosauria, had additional openings in the
snout
A snout is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw. In many animals, the structure is called a muzzle, rostrum, or proboscis. The wet furless surface around the nostrils of the nose of many mammals is c ...
and lower jaw. Additionally, several characteristics once thought to be synapomorphies are now known to have appeared before dinosaurs, or were absent in the earliest dinosaurs and independently evolved by different dinosaur groups. These include an elongated
scapula
The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on eithe ...
, or shoulder blade; a
sacrum
The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30.
The sacrum situates at the upper, back part ...
composed of three or more fused vertebrae (three are found in some other archosaurs, but only two are found in ''
Herrerasaurus
''Herrerasaurus'' is a genus of saurischian dinosaur from the Late Triassic period. This genus was one of the earliest dinosaurs from the fossil record. Its name means "Herrera's lizard", after the rancher who discovered the first specimen in ...
''); and a perforate
acetabulum
The acetabulum (), also called the cotyloid cavity, is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint.
Structure
There are three bones of the ''os coxae'' (hip bone) that c ...
, or hip socket, with a hole at the center of its inside surface (closed in ''
Saturnalia tupiniquim
''Saturnalia'' is an extinct genus of basal sauropodomorph dinosaur known from the Late Triassic Santa Maria Formation of Rio Grande do Sul, southern Brazil and possibly the Pebbly Arkose Formation, Zimbabwe.
Discovery and naming
''Saturnal ...
'', for example). Another difficulty of determining distinctly dinosaurian features is that early dinosaurs and other archosaurs from the
Late Triassic
The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch ...
epoch are often poorly known and were similar in many ways; these animals have sometimes been misidentified in the literature.
Dinosaurs stand with their hind limbs erect in a manner similar to most modern mammals, but distinct from most other reptiles, whose limbs sprawl out to either side. This posture is due to the development of a laterally facing recess in the pelvis (usually an open socket) and a corresponding inwardly facing distinct head on the femur. Their erect posture enabled early dinosaurs to breathe easily while moving, which likely permitted stamina and activity levels that surpassed those of "sprawling" reptiles. Erect limbs probably also helped support the
evolution
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
of large size by reducing bending stresses on limbs. Some non-dinosaurian archosaurs, including
rauisuchia
"Rauisuchia" is a paraphyletic group of mostly large and carnivorous Triassic archosaurs. Rauisuchians are a category of archosaurs within a larger group called Pseudosuchia, which encompasses all archosaurs more closely related to crocodilia
...
ns, also had erect limbs but achieved this by a "pillar-erect" configuration of the hip joint, where instead of having a projection from the femur insert on a socket on the hip, the upper pelvic bone was rotated to form an overhanging shelf.
History of study
Pre-scientific history
Dinosaur fossils have been known for millennia, although their true nature was not recognized. The Chinese considered them to be
dragon
A dragon is a reptilian legendary creature that appears in the folklore of many cultures worldwide. Beliefs about dragons vary considerably through regions, but dragons in western cultures since the High Middle Ages have often been depicted as ...
bones and documented them as such. For example, '' Huayang Guo Zhi'' (), a
gazetteer
A gazetteer is a geographical index or directory used in conjunction with a map or atlas.Aurousseau, 61. It typically contains information concerning the geographical makeup, social statistics and physical features of a country, region, or co ...
compiled by
Chang Qu
Chang Qu () (c. 291 – c. 361 CE) was a 4th-century Chinese historian of the Cheng Han dynasty, who wrote the ''Chronicles of Huayang'' or ''Records of the States South of Mount Hua
Mount Hua () is a mountain located near the city of Huayin ...
() during the
Western Jin Dynasty
Western may refer to:
Places
*Western, Nebraska, a village in the US
*Western, New York, a town in the US
*Western Creek, Tasmania, a locality in Australia
*Western Junction, Tasmania, a locality in Australia
*Western world, countries that id ...
(265–316), reported the discovery of dragon bones at Wucheng in
Sichuan
Sichuan (; zh, c=, labels=no, ; zh, p=Sìchuān; alternatively romanized as Szechuan or Szechwan; formerly also referred to as "West China" or "Western China" by Protestant missions) is a province in Southwest China occupying most of the ...
Province. Villagers in central
China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
have long unearthed fossilized "dragon bones" for use in
traditional medicines
Traditional medicine (also known as indigenous medicine or folk medicine) comprises medical aspects of traditional knowledge that developed over generations within the folk beliefs of various societies, including indigenous peoples, before the ...
. In
Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
, dinosaur fossils were generally believed to be the remains of
giant
In folklore, giants (from Ancient Greek: '' gigas'', cognate giga-) are beings of human-like appearance, but are at times prodigious in size and strength or bear an otherwise notable appearance. The word ''giant'' is first attested in 1297 fr ...
s and other
biblical
The Bible (from Koine Greek , , 'the books') is a collection of religious texts or scriptures that are held to be sacred in Christianity, Judaism, Samaritanism, and many other religions. The Bible is an anthologya compilation of texts of a ...
creatures.
Early dinosaur research
Scholarly descriptions of what would now be recognized as dinosaur bones first appeared in the late 17th century in England. Part of a bone, now known to have been the femur of a ''Megalosaurus'', was recovered from a limestone quarry at
Cornwell Cornwell can refer to: People
* Almon Cornwell (1820–1893), American farmer-politician in Wisconsin
* Anita Cornwell (1923–2023), American author
* Bernard Cornwell (born 1944), British historical novelist
* Charlotte Cornwell (1949–2021), Bri ...
near
Chipping Norton
Chipping Norton is a market town and civil parish in the Cotswold Hills in the West Oxfordshire district of Oxfordshire, England, about south-west of Banbury and north-west of Oxford. The 2011 Census recorded the civil parish population as ...
, Oxfordshire, in 1676. The fragment was sent to
Robert Plot
Robert Plot (13 December 1640 – 30 April 1696) was an English naturalist, first Professor of Chemistry at the University of Oxford, and the first keeper of the Ashmolean Museum.
Early life and education
Born in Borden, Kent to parents Robe ...
, Professor of Chemistry at the
University of Oxford
, mottoeng = The Lord is my light
, established =
, endowment = £6.1 billion (including colleges) (2019)
, budget = £2.145 billion (2019–20)
, chancellor ...
and first curator of the
Ashmolean Museum
The Ashmolean Museum of Art and Archaeology () on Beaumont Street, Oxford, England, is Britain's first public museum. Its first building was erected in 1678–1683 to house the cabinet of curiosities that Elias Ashmole gave to the University of ...
, who published a description in his ''The Natural History of Oxford-shire'' (1677). He correctly identified the bone as the lower extremity of the femur of a large animal, and recognized that it was too large to belong to any known species. He, therefore, concluded it to be the femur of a huge human, perhaps a
Titan
Titan most often refers to:
* Titan (moon), the largest moon of Saturn
* Titans, a race of deities in Greek mythology
Titan or Titans may also refer to:
Arts and entertainment
Fictional entities
Fictional locations
* Titan in fiction, fictiona ...
or another type of giant featured in legends.
Edward Lhuyd
Edward Lhuyd FRS (; occasionally written Llwyd in line with modern Welsh orthography, 1660 – 30 June 1709) was a Welsh naturalist, botanist, linguist, geographer and antiquary. He is also named in a Latinate form as Eduardus Luidius.
Life
...
, a friend of
Sir Isaac Newton
Sir Isaac Newton (25 December 1642 – 20 March 1726/27) was an English mathematician, physicist, astronomer, alchemist, theologian, and author (described in his time as a "natural philosopher"), widely recognised as one of the great ...
, published ''Lithophylacii Britannici ichnographia'' (1699), the first scientific treatment of what would now be recognized as a dinosaur when he described and named a sauropod
tooth
A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...
Witney
Witney is a market town on the River Windrush in West Oxfordshire in the county of Oxfordshire, England. It is west of Oxford. The place-name "Witney" is derived from the Old English for "Witta's island". The earliest known record of it is as ...
, Oxfordshire.
Between 1815 and 1824, the Rev
William Buckland
William Buckland Doctor of Divinity, DD, Royal Society, FRS (12 March 1784 – 14 August 1856) was an English theologian who became Dean of Westminster. He was also a geologist and paleontology, palaeontologist.
Buckland wrote the first full ...
, the first Reader of Geology at the University of Oxford, collected more fossilized bones of ''Megalosaurus'' and became the first person to describe a non-avian dinosaur in a
scientific journal
In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research.
Content
Articles in scientific journals are mostly written by active scientists such as s ...
. The second non-avian dinosaur genus to be identified, ''Iguanodon'', was discovered in 1822 by
Mary Ann Mantell
Mary Ann Mantell ('' née'' Woodhouse; 9 April 1795 – 20 October 1869) was a British fossil collector and the wife of the British paleontologist Gideon Mantell. She is credited – although this is disputed – with the discovery of the first fo ...
– the wife of English geologist
Gideon Mantell
Gideon Algernon Mantell MRCS FRS (3 February 1790 – 10 November 1852) was a British obstetrician, geologist and palaeontologist. His attempts to reconstruct the structure and life of ''Iguanodon'' began the scientific study of dinosaurs: in ...
. Gideon Mantell recognized similarities between his fossils and the bones of modern
iguana
''Iguana'' (, ) is a genus of herbivorous lizards that are native to tropical areas of Mexico, Central America, South America, and the Caribbean. The genus was first described in 1768 by Austrian naturalist Josephus Nicolaus Laurenti in his bo ...
s. He published his findings in 1825.
The study of these "great fossil lizards" soon became of great interest to European and American scientists, and in 1841 the English paleontologist Sir Richard Owen coined the term "dinosaur", using it to refer to the "distinct tribe or sub-order of Saurian Reptiles" that were then being recognized in England and around the world. The term is derived . Though the taxonomic name has often been interpreted as a reference to dinosaurs' teeth, claws, and other fearsome characteristics, Owen intended it to also evoke their size and majesty. Owen recognized that the remains that had been found so far, ''Iguanodon'', ''Megalosaurus'' and ''
Hylaeosaurus
''Hylaeosaurus'' ( ; Greek: / "belonging to the forest" and / "lizard") is a herbivorous ankylosaurian dinosaur that lived about 136 million years ago, in the late Valanginian stage of the early Cretaceous period of England. It was found in ...
'', shared a number of distinctive features, and so decided to present them as a distinct taxonomic group. With the backing of Prince Albert, the husband of
Queen Victoria
Victoria (Alexandrina Victoria; 24 May 1819 – 22 January 1901) was Queen of the United Kingdom of Great Britain and Ireland from 20 June 1837 until Death and state funeral of Queen Victoria, her death in 1901. Her reign of 63 years and 21 ...
, Owen established the
Natural History Museum, London
The Natural History Museum in London is a museum that exhibits a vast range of specimens from various segments of natural history. It is one of three major museums on Exhibition Road in South Kensington, the others being the Science Museum an ...
, to display the national collection of dinosaur fossils and other biological and geological exhibits.
Discoveries in North America
In 1858,
William Parker Foulke
William Parker Foulke (1816–1865) discovered the first full dinosaur skeleton in North America (''Hadrosaurus foulkii'', which means "Foulke's big lizard") in Haddonfield, New Jersey in 1858.
Born in Philadelphia, and a descendant of Welsh Qu ...
discovered the first known American dinosaur, in
marl
Marl is an earthy material rich in carbonate minerals, clays, and silt. When hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae.
Marl makes up the lower part o ...
pits in the small town of
Haddonfield, New Jersey
:''Not the fictional Illinois town from the Halloween film series.''
Haddonfield is a borough located in Camden County, New Jersey, United States. As of the 2010 United States Census, the borough had a total population of 11,593,
. (Although fossils had been found before, their nature had not been correctly discerned.) The creature was named ''
Hadrosaurus foulkii
''Hadrosaurus'' (; ) is a genus of hadrosaurid ornithopod dinosaurs that lived in North America during the Late Cretaceous Period in what is now the Woodbury Formation about 80 million to 78 million years ago. The holotype specimen was found i ...
''. It was an extremely important find: ''Hadrosaurus'' was one of the first nearly complete dinosaur skeletons found (
the first The First may refer to:
* ''The First'' (album), the first Japanese studio album by South Korean boy group Shinee
* ''The First'' (musical), a musical with a book by critic Joel Siegel
* The First (TV channel), an American conservative opinion ne ...
was in 1834, in Maidstone, England), and it was clearly a bipedal creature. This was a revolutionary discovery as, until that point, most scientists had believed dinosaurs walked on four feet, like other lizards. Foulke's discoveries sparked a wave of interests in dinosaurs in the United States, known as dinosaur mania.
Dinosaur mania was exemplified by the fierce rivalry between
Edward Drinker Cope
Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontologist, comparative anatomist, herpetologist, and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested ...
and
Othniel Charles Marsh
Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of Paleontology in Yale College and President of the National Academy of Sciences. He was one of the preeminent scientists in the field of paleontology. Among h ...
, both of whom raced to be the first to find new dinosaurs in what came to be known as the
Bone Wars
The Bone Wars, also known as the Great Dinosaur Rush, was a period of intense and ruthlessly competitive fossil hunting and discovery during the Gilded Age of American history, marked by a heated rivalry between Edward Drinker Cope (of the Acade ...
. This fight between the two scientists lasted for over 30 years, ending in 1897 when Cope died after spending his entire fortune on the dinosaur hunt. Unfortunately, many valuable dinosaur specimens were damaged or destroyed due to the pair's rough methods: for example, their diggers often used
dynamite
Dynamite is an explosive made of nitroglycerin, sorbents (such as powdered shells or clay), and Stabilizer (chemistry), stabilizers. It was invented by the Swedish people, Swedish chemist and engineer Alfred Nobel in Geesthacht, Northern Germa ...
to unearth bones. Modern paleontologists would find such methods crude and unacceptable, since blasting easily destroys fossil and stratigraphic evidence. Despite their unrefined methods, the contributions of Cope and Marsh to paleontology were vast: Marsh unearthed 86 new species of dinosaur and Cope discovered 56, a total of 142 new species. Cope's collection is now at the
American Museum of Natural History
The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 inter ...
in New York City, while Marsh's is at the
Peabody Museum of Natural History
The Peabody Museum of Natural History at Yale University is among the oldest, largest, and most prolific university natural history museums in the world. It was founded by the philanthropist George Peabody in 1866 at the behest of his nephew Othn ...
at
Yale University
Yale University is a private research university in New Haven, Connecticut. Established in 1701 as the Collegiate School, it is the third-oldest institution of higher education in the United States and among the most prestigious in the wo ...
.
"Dinosaur renaissance" and beyond
The field of dinosaur research has enjoyed a surge in activity that began in the 1970s and is ongoing. This was triggered, in part, by
John Ostrom
John Harold Ostrom (February 18, 1928 – July 16, 2005) was an American paleontologist who revolutionized modern understanding of dinosaurs in the 1960s.
As first proposed by Thomas Henry Huxley in the 1860s, Ostrom showed that dinosaurs were ...
's discovery and 1969 description of ''
Deinonychus
''Deinonychus'' ( ; ) is a genus of dromaeosaurid theropod dinosaur with one described species, ''Deinonychus antirrhopus''. This species, which could grow up to long, lived during the early Cretaceous Period, about 115–108 million ye ...
'', an active predator that may have been warm-blooded, in marked contrast to the then-prevailing image of dinosaurs as sluggish and cold-blooded.
Vertebrate paleontology
Vertebrate paleontology is the subfield of paleontology that seeks to discover, through the study of fossilized remains, the behavior, reproduction and appearance of extinct animals with vertebrae or a notochord. It also tries to connect, by us ...
has become a global
science
Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe.
Science may be as old as the human species, and some of the earliest archeological evidence for ...
. Major new dinosaur discoveries have been made by paleontologists working in previously unexploited regions, including India, South America, Madagascar, Antarctica, and most significantly China (the well-preserved feathered dinosaurs in China have further consolidated the link between dinosaurs and their living descendants, modern birds). The widespread application of
cladistics
Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups (" clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...
, which rigorously analyzes the relationships between biological organisms, has also proved tremendously useful in classifying dinosaurs. Cladistic analysis, among other modern techniques, helps to compensate for an often incomplete and fragmentary fossil record.
Soft tissue and DNA
One of the best examples of soft-tissue impressions in a fossil dinosaur was discovered in the
Pietraroja Plattenkalk
The Pietraroia Plattenkalk is a Cretaceous geologic formation located in the Italian municipality of Pietraroja,
in southern
Italy
Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical re ...
. The discovery was reported in 1998, and described the specimen of a small, juvenile coelurosaur, ''
Scipionyx samniticus
''Scipionyx'' ( ) was a genus of theropod dinosaur from the Early Cretaceous of Italy, around 113 million years ago.
There is only one fossil known of ''Scipionyx'', discovered in 1981 by an amateur paleontologist and brought to the attention o ...
''. The fossil includes portions of the intestines, colon, liver, muscles, and windpipe of this dinosaur.
In the March 2005 issue of ''
Science
Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe.
Science may be as old as the human species, and some of the earliest archeological evidence for ...
'', the paleontologist
Mary Higby Schweitzer
Mary Higby Schweitzer is an American paleontologist at North Carolina State University, who led the groups that discovered the remains of blood cells in dinosaur fossils and later discovered soft tissue remains in the ''Tyrannosaurus rex'' specime ...
and her team announced the discovery of flexible material resembling actual soft tissue inside a 68-million-year-old ''Tyrannosaurus rex'' leg bone from the
Hell Creek Formation
The Hell Creek Formation is an intensively studied division of mostly Upper Cretaceous and some lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana. The formation stretches over portions of ...
in
Montana
Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columbi ...
. After recovery, the tissue was rehydrated by the science team. When the fossilized bone was treated over several weeks to remove mineral content from the fossilized bone-marrow cavity (a process called demineralization), Schweitzer found evidence of intact structures such as
blood vessel
The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away ...
s,
bone matrix
In osteology, the osteon or haversian system (; named for Clopton Havers) is the fundamental functional unit of much compact bone. Osteons are roughly cylindrical structures that are typically between 0.25 mm and 0.35 mm in diameter. Their ...
, and connective tissue (bone fibers). Scrutiny under the microscope further revealed that the putative dinosaur soft tissue had retained fine structures (microstructures) even at the cellular level. The exact nature and composition of this material, and the implications of Schweitzer's discovery, are not yet clear.
In 2009, a team including Schweitzer announced that, using even more careful methodology, they had duplicated their results by finding similar soft tissue in a duck-billed dinosaur, ''
Brachylophosaurus canadensis
''Brachylophosaurus'' ( or ; meaning "short-crested lizard", Greek ''brachys'' = short + ''lophos'' = crest + ''sauros'' = lizard, referring to its small crest) was a mid-sized member of the hadrosaurid family of dinosaurs. It is known from sev ...
'', found in the
Judith River Formation
The Judith River Formation is a fossil-bearing geologic formation in Montana, and is part of the Judith River Group. It dates to the Late Cretaceous, between 79 and 75.3 million years ago, corresponding to the "Judithian" land vertebrate age. It ...
of Montana. This included even more detailed tissue, down to preserved bone cells that seem to have visible remnants of nuclei and what seem to be red blood cells. Among other materials found in the bone was
collagen
Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole ...
, as in the ''Tyrannosaurus'' bone. The type of collagen an animal has in its bones varies according to its DNA and, in both cases, this collagen was of the same type found in modern chickens and ostriches.
The extraction of ancient DNA from dinosaur fossils has been reported on two separate occasions; upon further inspection and
peer review
Peer review is the evaluation of work by one or more people with similar competencies as the producers of the work (peers). It functions as a form of self-regulation by qualified members of a profession within the relevant field. Peer review ...
, however, neither of these reports could be confirmed. However, a functional
peptide
Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides.
A ...
involved in the vision of a theoretical dinosaur has been inferred using analytical phylogenetic reconstruction methods on gene sequences of related modern species such as reptiles and birds. In addition, several
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
s, including
hemoglobin
Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyte ...
, have putatively been detected in dinosaur fossils.
In 2015, researchers reported finding structures similar to blood cells and collagen fibers, preserved in the bone fossils of six Cretaceous dinosaur specimens, which are approximately 75 million years old.
Evolutionary history
Origins and early evolution
Dinosaurs diverged from their archosaur ancestors during the Middle to Late Triassic epochs, roughly 20 million years after the devastating
Permian–Triassic extinction event
The Permian–Triassic (P–T, P–Tr) extinction event, also known as the Latest Permian extinction event, the End-Permian Extinction and colloquially as the Great Dying, formed the boundary between the Permian and Triassic geologic periods, as ...
wiped out an estimated 96% of all marine species and 70% of terrestrial vertebrate species approximately 252 million years ago.
Radiometric dating
Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares t ...
of the
Ischigualasto Formation
The Ischigualasto Formation is a Late Triassic fossiliferous formation and Lagerstätte in the Ischigualasto-Villa Unión Basin of the southwestern La Rioja Province and northeastern San Juan Province in northwestern Argentina. The formation da ...
of Argentina where the early dinosaur
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
''
Eoraptor
''Eoraptor'' () is a genus of small, lightly built, basal sauropodomorph. One of the earliest-known dinosaurs, it lived approximately 231 to 228 million years ago, during the Late Triassic in Western Gondwana, in the region that is now northwest ...
'' was found date it as 231.4 million years old. ''Eoraptor'' is thought to resemble the
common ancestor
Common descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time. All living beings are in fact descendants of a unique ancestor commonly referred to as the last universal comm ...
of all dinosaurs; if this is true, its traits suggest that the first dinosaurs were small, bipedal
predators
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...
. The discovery of primitive, dinosaur-like ornithodirans such as ''
Lagosuchus
''Lagosuchus'' is an extinct genus of avemetatarsalian archosaur from the Late Triassic of Argentina. The type species of ''Lagosuchus'', ''Lagosuchus talampayensis,'' is based on a small partial skeleton recovered from the early Carnian-age Cha ...
'' and ''
Lagerpeton
''Lagerpeton'' is a genus of lagerpetid avemetatarsalian, comprising a single species, ''L. chanarensis''. First described from the Chañares Formation of Argentina by A. S. Romer in 1971, ''Lagerpeton'' anatomy is somewhat incompletely kn ...
'' in
Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
in the
Carnian
The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic Series (or earliest age of the Late Triassic Epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followed by t ...
epoch of the Triassic, around 233 million years ago, supports this view; analysis of recovered fossils suggests that these animals were indeed small, bipedal predators. Dinosaurs may have appeared as early as the
Anisian
In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from million years ago until million years ago. The Anisian Age succeeds the Olenekian Age (part of the Lower Triassic Ep ...
epoch of the Triassic, 245 million years ago, as evidenced by remains of the genus ''
Nyasasaurus
''Nyasasaurus'' (meaning " Lake Nyasa lizard") is an extinct genus of avemetatarsalian archosaur from the putatively Middle Triassic Manda Formation of Tanzania that may be the earliest known dinosaur. The type species ''Nyasasaurus parringtoni' ...
'' from that period. However, its known fossils are too fragmentary to tell if it was a dinosaur or only a close relative. Paleontologist Max C. Langer ''et al.'' (2018) determined that ''
Staurikosaurus
''Staurikosaurus'' (Pronounced "STORE-ee-koh-SAWR-us", "Southern Cross lizard") is a genus of herrerasaurid dinosaur from the Late Triassic of Brazil, found in the Santa Maria Formation.
Description
Colbert (1970) described ''Staurikosaurus' ...
'' from the
Santa Maria Formation
The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It is primarily Carnian in age (Late Triassic), and is notable for its fossils of cynodonts, "rauisuchian" pseudosuchians, and early dinosaurs and oth ...
dates to 233.23 million years ago, making it older in geologic age than ''Eoraptor''.
When dinosaurs appeared, they were not the dominant terrestrial animals. The terrestrial habitats were occupied by various types of
archosauromorphs
Archosauromorpha (Greek for "ruling lizard forms") is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs (such as crocodilians and dinosaurs, including birds) rather than lepidosaurs (such as tuataras, liz ...
and
therapsid
Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...
s, like
cynodont
The cynodonts () (clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide variety ...
s and
rhynchosaur
Rhynchosaurs are a group of extinct herbivorous Triassic archosauromorph reptiles, belonging to the order Rhynchosauria. Members of the group are distinguished by their triangular skulls and elongated, beak like premaxillary bones. Rhynchosaurs ...
s. Their main competitors were the
pseudosuchians
Pseudosuchia is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely related to crocodilians than to birds. Pseudosuchians are also informally known as "crocodilian-line archosaurs". Prior to ...
, such as
aetosaur
Aetosaurs () are heavily armored reptiles belonging to the extinct order Aetosauria (; from Greek, (aetos, "eagle") and (, "lizard")). They were medium- to large-sized omnivorous or herbivorous pseudosuchians, part of the branch of archosaurs ...
s,
ornithosuchids
Ornithosuchidae is an extinct family of pseudosuchian archosaurs (distant relatives of modern crocodilians) from the Triassic period. Ornithosuchids were quadrupedal and facultatively bipedal (e.g. like chimpanzees), meaning that they had the a ...
and rauisuchians, which were more successful than the dinosaurs. Most of these other animals became extinct in the Triassic, in one of two events. First, at about 215 million years ago, a variety of basal archosauromorphs, including the protorosaurs, became extinct. This was followed by the Triassic–Jurassic extinction event (about 201 million years ago), that saw the end of most of the other groups of early archosaurs, like aetosaurs, ornithosuchids,
phytosaur
Phytosaurs (Φυτόσαυροι in greek) are an extinct group of large, mostly semiaquatic Late Triassic archosauriform reptiles. Phytosaurs belong to the order Phytosauria. Phytosauria and Phytosauridae are often considered to be equivalent ...
s, and rauisuchians. Rhynchosaurs and
dicynodont
Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivorous animals with a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, typicall ...
s survived (at least in some areas) at least as late as early –mid
Norian
The Norian is a division of the Triassic Period. It has the rank of an age (geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.
Stratigraphic defi ...
and late Norian or earliest
Rhaetian
The Rhaetian is the latest age of the Triassic Period (in geochronology) or the uppermost stage of the Triassic System (in chronostratigraphy). It was preceded by the Norian and succeeded by the Hettangian (the lowermost stage or earliest age ...
stage
Stage or stages may refer to:
Acting
* Stage (theatre), a space for the performance of theatrical productions
* Theatre, a branch of the performing arts, often referred to as "the stage"
* ''The Stage'', a weekly British theatre newspaper
* Sta ...
s, respectively, and the exact date of their
extinction
Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
is uncertain. These losses left behind a land fauna of
crocodylomorphs
Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction.
During Mesozoic and early Cenozoic times, cr ...
, dinosaurs, mammals, pterosaurians, and
turtle
Turtles are an order of reptiles known as Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked tu ...
s. The first few lines of early dinosaurs diversified through the Carnian and Norian stages of the Triassic, possibly by occupying the niches of the groups that became extinct. Also notably, there was a heightened rate of extinction during the
Carnian pluvial event
The Carnian pluvial episode (CPE), often called the Carnian pluvial event, was an interval of major change in global climate synchronous with significant changes in Earth's biota both in the sea and on land. It occurred during the latter part of ...
.
Evolution and paleobiogeography
Dinosaur evolution after the Triassic followed changes in vegetation and the location of continents. In the Late Triassic and Early Jurassic, the continents were connected as the single landmass
Pangaea
Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...
, and there was a worldwide dinosaur fauna mostly composed of
coelophysoid
Coelophysoidea were common dinosaurs of the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivorous forms with a superficial similarity to the ...
carnivores and early sauropodomorph herbivores.
Gymnosperm
The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, ''Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμνό ...
plants (particularly
conifer
Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single ...
s), a potential food source, radiated in the Late Triassic. Early sauropodomorphs did not have sophisticated mechanisms for processing food in the mouth, and so must have employed other means of breaking down food farther along the digestive tract. The general homogeneity of dinosaurian faunas continued into the Middle and Late Jurassic, where most localities had predators consisting of
ceratosauria
Ceratosaurs are members of the clade Ceratosauria, a group of dinosaurs defined as all theropods sharing a more recent common ancestor with ''Ceratosaurus'' than with birds. The oldest known ceratosaur, ''Saltriovenator'', dates to the earliest ...
ns, megalosauroids, and allosauroids, and herbivores consisting of stegosaurian ornithischians and large sauropods. Examples of this include the
Morrison Formation
The Morrison Formation is a distinctive sequence of Late Jurassic, Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandsto ...
of
North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
and Tendaguru Beds of Tanzania. Dinosaurs in China show some differences, with specialized
metriacanthosaurid
Metriacanthosauridae is an extinct family (biology), family of Allosauroidea, allosauroid theropod dinosaurs that lived from the Middle Jurassic to the Early Cretaceous. When broken down into its Greek roots, it means "moderately-spined lizards". ...
theropods and unusual, long-necked sauropods like ''
Mamenchisaurus
''Mamenchisaurus'' (or spelling pronunciation ) is a genus of sauropod dinosaur known for their remarkably long necks which made up nearly half the total body length. Numerous species have been assigned to the genus; however, many of these might ...
''. Ankylosaurians and ornithopods were also becoming more common, but primitive sauropodomorphs had become extinct. Conifers and
pteridophyte
A pteridophyte is a vascular plant (with xylem and phloem) that disperses spores. Because pteridophytes produce neither flowers nor seeds, they are sometimes referred to as "cryptogams", meaning that their means of reproduction is hidden. Ferns, ...
s were the most common plants. Sauropods, like earlier sauropodomorphs, were not oral processors, but ornithischians were evolving various means of dealing with food in the mouth, including potential
cheek
The cheeks ( la, buccae) constitute the area of the face below the eyes and between the nose and the left or right ear. "Buccal" means relating to the cheek. In humans, the region is innervated by the buccal nerve. The area between the inside ...
-like organs to keep food in the mouth, and jaw motions to grind food. Another notable evolutionary event of the Jurassic was the appearance of true birds, descended from maniraptoran coelurosaurians.
By the
Early Cretaceous
The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma.
Geology
Pro ...
and the ongoing breakup of Pangaea, dinosaurs were becoming strongly differentiated by landmass. The earliest part of this time saw the spread of ankylosaurians,
iguanodontia
Iguanodontia (the iguanodonts) is a clade of herbivorous dinosaurs that lived from the Middle Jurassic to Late Cretaceous. Some members include ''Camptosaurus'', ''Dryosaurus'', ''Iguanodon'', ''Tenontosaurus'', and the hadrosaurids or "duck-bi ...
ns, and
brachiosaurids
The Brachiosauridae ("arm lizards", from Greek ''brachion'' (βραχίων) = "arm" and ''sauros'' = "lizard") are a family or clade of herbivorous, quadrupedal sauropod dinosaurs. Brachiosaurids had long necks that enabled them to access the le ...
through Europe, North America, and northern
Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
. These were later supplemented or replaced in Africa by large spinosaurid and
carcharodontosaurid
Carcharodontosauridae (carcharodontosaurids; from the Greek καρχαροδοντόσαυρος, ''carcharodontósauros'': "shark-toothed lizards") is a group of carnivorous theropod dinosaurs. In 1931, Ernst Stromer named Carcharodontosauridae ...
theropods, and
rebbachisaurid
Rebbachisauridae is a family of sauropod dinosaurs known from fragmentary fossil remains from the Cretaceous of South America, Africa, North America, Europe and possibly Central Asia.
Taxonomy
In 1990 sauropod specialist Jack McIntosh included t ...
and
titanosauria
Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still thr ...
n sauropods, also found in
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...
. In
Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...
, maniraptoran coelurosaurians like
dromaeosaurids
Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...
,
troodontids
Troodontidae is a clade of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinosaurian lineages. More recent fossil discov ...
, and
oviraptorosauria
Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like skulls, with or wit ...
ns became the common theropods, and
ankylosaurids
Ankylosauridae () is a family of armored dinosaurs within Ankylosauria, and is the sister group to Nodosauridae. The oldest known Ankylosaurids date to around 122 million years ago and went extinct 66 million years ago during the Cretaceous–Pal ...
and early ceratopsians like ''Psittacosaurus'' became important herbivores. Meanwhile,
Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
was home to a fauna of basal ankylosaurians,
hypsilophodont
Hypsilophodontidae (or Hypsilophodontia) is a traditionally used family of ornithopod dinosaurs, generally considered invalid today. It historically included many small bodied bipedal neornithischian taxa from around the world, and spanning from ...
s, and iguanodontians. The stegosaurians appear to have gone extinct at some point in the late Early Cretaceous or early
Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
. A major change in the Early Cretaceous, which would be amplified in the Late Cretaceous, was the evolution of
flowering plant
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...
s. At the same time, several groups of dinosaurian herbivores evolved more sophisticated ways to orally process food. Ceratopsians developed a method of slicing with teeth stacked on each other in batteries, and iguanodontians refined a method of grinding with
dental batteries
Dinosaur teeth have been studied since 1822 when Mary Ann Mantell (1795-1869) and her husband Dr Gideon Algernon Mantell (1790-1852) discovered an ''Iguanodon'' tooth in Sussex in England. Unlike mammal teeth, individual dinosaur teeth are gener ...
, taken to its extreme in hadrosaurids. Some sauropods also evolved tooth batteries, best exemplified by the rebbachisaurid ''
Nigersaurus
''Nigersaurus'' is a genus of rebbachisaurid sauropod dinosaur that lived during the middle Cretaceous period, about 115 to 105 million years ago. It was discovered in the Elrhaz Formation in an area called Gadoufaoua, in Niger. Fossils of th ...
''.
There were three general dinosaur faunas in the Late Cretaceous. In the northern continents of North America and Asia, the major theropods were
tyrannosaurids
Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family (biology), family of coelurosaurian Theropoda, theropod dinosaurs that comprises two subfamilies containing up to thirteen genus, genera, including the eponymous ''Tyrannos ...
and various types of smaller maniraptoran theropods, with a predominantly ornithischian herbivore assemblage of hadrosaurids, ceratopsians, ankylosaurids, and pachycephalosaurians. In the southern continents that had made up the now-splitting supercontinent
Gondwana
Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...
,
abelisaurids
Abelisauridae (meaning "Abel's lizards") is a family (or clade) of ceratosaurian theropod dinosaurs. Abelisaurids thrived during the Cretaceous period, on the ancient southern supercontinent of Gondwana, and today their fossil remains are found ...
were the common theropods, and titanosaurian sauropods the common herbivores. Finally, in Europe, dromaeosaurids,
rhabdodontid
Rhabdodontidae is a family of herbivorous iguanodontian ornithopod dinosaurs whose earliest stem members appeared in the middle of the Lower Cretaceous. The oldest dated fossils of these stem members were found in the Barremian Castrillo de la R ...
iguanodontians,
nodosaurid
Nodosauridae is a family of ankylosaurian dinosaurs, from the Late Jurassic to the Late Cretaceous period in what is now North America, South America, Europe, and Asia.
Description
Nodosaurids, like their close relatives the ankylosaurids, wer ...
ankylosaurians, and titanosaurian sauropods were prevalent. Flowering plants were greatly radiating, with the first grasses appearing by the end of the Cretaceous. Grinding hadrosaurids and shearing ceratopsians became very diverse across North America and Asia. Theropods were also radiating as herbivores or
omnivore
An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nutr ...
s, with
therizinosaur
Therizinosaurs (once called segnosaurs) were large herbivorous Theropoda, theropod dinosaurs whose fossils have been found across the Early Cretaceous, Early to Late Cretaceous deposits in Asia and North America. Various features of the forelimbs ...
ians and
ornithomimosauria
Ornithomimosauria ("bird-mimic lizards") are theropod dinosaurs which bore a superficial resemblance to the modern-day ostrich. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period (geology), Period of Laurasia (now Asia ...
ns becoming common.
The Cretaceous–Paleogene extinction event, which occurred approximately 66 million years ago at the end of the Cretaceous, caused the extinction of all dinosaur groups except for the neornithine birds. Some other diapsid groups, including
crocodilia
Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period ( Cenomanian stage) and are the closest living ...
sebecosuchia
Sebecosuchia is an extinct group of mesoeucrocodylian crocodyliforms that includes the families Sebecidae and Baurusuchidae. The group was long thought to have first appeared in the Late Cretaceous with the baurusuchids and become extinct in the ...
ns, turtles,
lizard
Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...
s,
snake
Snakes are elongated, Limbless vertebrate, limbless, carnivore, carnivorous reptiles of the suborder Serpentes . Like all other Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in overlapping Scale (zoology), scales. Ma ...
choristodera
Choristodera (from the Greek χωριστός ''chōristos'' + δέρη ''dérē'', 'separated neck') is an extinct order of semiaquatic diapsid reptiles that ranged from the Middle Jurassic, or possibly Triassic, to the late Miocene (168 to 1 ...
ns, also survived the event.
The surviving lineages of neornithine birds, including the ancestors of modern
ratite
A ratite () is any of a diverse group of flightless, large, long-necked, and long-legged birds of the infraclass Palaeognathae. Kiwi, the exception, are much smaller and shorter-legged and are the only nocturnal extant ratites.
The systematics ...
waterbirds
A water bird, alternatively waterbird or aquatic bird, is a bird that lives on or around water. In some definitions, the term ''water bird'' is especially applied to birds in freshwater ecosystems, although others make no distinction from seabi ...
, diversified rapidly at the beginning of the
Paleogene
The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...
period, entering
ecological niche
In ecology, a niche is the match of a species to a specific environmental condition.
Three variants of ecological niche are described by
It describes how an organism or population responds to the distribution of resources and competitors (for ...
s left vacant by the extinction of Mesozoic dinosaur groups such as the arboreal
enantiornithine
The Enantiornithes, also known as enantiornithines or enantiornitheans in literature, are a group of extinct avialans ("birds" in the broad sense), the most abundant and diverse group known from the Mesozoic era. Almost all retained teeth and cla ...
s, aquatic
hesperornithine
Hesperornithes is an extinct and highly specialized group of aquatic avialans closely related to the ancestors of modern birds. They inhabited both marine and freshwater habitats in the Northern Hemisphere, and include genera such as ''Hesperorni ...
s, and even the larger terrestrial theropods (in the form of ''
Gastornis
''Gastornis'' is an extinct genus of large flightless birds that lived during the mid Paleocene to mid Eocene epochs of the Paleogene period. Fossils have been found in Europe, Asia and North America, with the remains from North America origina ...
'',
eogruiids
Eogruidae (also spelled Eogruiidae in some publications) is a family of large, flightless birds that inhabited Asia from the Eocene to Pliocene epochs. Related to modern ostriches, it was formerly thought to be related to cranes, limpkins and tr ...
,
bathornithids
Bathornithidae is an extinct family of birds from the Eocene to Miocene of North America. Part of Cariamiformes, they are related to the still extant seriemas and the also extinct Phorusrhacidae. They were likely similar in habits, being terrestr ...
mihirung
Dromornithidae, known as mihirungs and informally as thunder birds or demon ducks, were a clade of large, flightless Australian birds of the Oligocene through Pleistocene Epochs. All are now extinct. They were long classified in Struthioniformes, ...
s, and "
terror bird
Phorusrhacids, colloquially known as terror birds, are an extinct clade of large carnivorous flightless birds that were one of the largest species of apex predators in South America during the Cenozoic era; their conventionally accepted temporal ...
s"). It is often stated that mammals out-competed the neornithines for dominance of most terrestrial niches but many of these groups co-existed with rich mammalian faunas for most of the
Cenozoic
The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...
Era. Terror birds and bathornithids occupied carnivorous guilds alongside predatory mammals, and ratites are still fairly successful as mid-sized herbivores; eogruiids similarly lasted from the
Eocene
The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...
to
Pliocene
The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58
Collectively, dinosaurs as a clade are divided into two primary branches, Saurischia and Ornithischia. Saurischia includes those taxa sharing a more recent common ancestor with birds than with Ornithischia, while Ornithischia includes all
taxa
In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
sharing a more recent common ancestor with ''Triceratops'' than with Saurischia. Anatomically, these two groups can be distinguished most noticeably by their
pelvic
The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton).
The ...
structure. Early saurischians—"lizard-hipped", from the
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
' () meaning "lizard" and ' () meaning "hip joint"—retained the hip structure of their ancestors, with a pubis bone directed
cranially
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
, or forward. This basic form was modified by rotating the pubis backward to varying degrees in several groups (''Herrerasaurus'', therizinosauroids, dromaeosaurids, and birds). Saurischia includes the theropods (exclusively bipedal and with a wide variety of diets) and sauropodomorphs (long-necked herbivores which include advanced, quadrupedal groups).
By contrast, ornithischians—"bird-hipped", from the Greek ''ornitheios'' (ὀρνίθειος) meaning "of a bird" and ''ischion'' (ἰσχίον) meaning "hip joint"—had a pelvis that superficially resembled a bird's pelvis: the pubic bone was oriented caudally (rear-pointing). Unlike birds, the ornithischian pubis also usually had an additional forward-pointing process. Ornithischia includes a variety of species that were primarily herbivores.
Despite the terms "bird hip" (Ornithischia) and "lizard hip" (Saurischia), birds are not part of Ornithischia. Birds instead belong to Saurischia, the “lizard-hipped” dinosaurs—birds evolved from earlier dinosaurs with "lizard hips".
Taxonomy
The following is a simplified classification of dinosaur groups based on their evolutionary relationships, and those of the main dinosaur groups Theropoda, Sauropodomorpha and Ornithischia, compiled by Justin Tweet. Further details and other hypotheses of classification may be found on individual articles.
*Dinosauria
:*†
Ornithischia
Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek s ...
("bird-hipped"; diverse bipedal and quadrupedal herbivores)
::*†
Heterodontosauridae
Heterodontosauridae is a family of ornithischian dinosaurs that were likely among the most basal (primitive) members of the group. Their phylogenetic placement is uncertain but they are most commonly found to be primitive, outside of the group ...
Genasauria
Genasauria is a clade of extinct beaked, primarily herbivorous dinosaurs. Paleontologist Paul Sereno first named Genasauria in 1986. The name Genasauria is derived from the Latin word ''gena'' meaning ‘cheek’ and the Greek word ''saúra'' (σ ...
("cheeked lizards")
::::*†
Thyreophora
Thyreophora ("shield bearers", often known simply as "armored dinosaurs") is a group of armored ornithischian dinosaurs that lived from the Early Jurassic until the end of the Cretaceous.
Thyreophorans are characterized by the presence of body ...
(armored dinosaurs; bipeds and quadrupeds)
:::::*†
Eurypoda
Thyreophora ("shield bearers", often known simply as "armored dinosaurs") is a group of armored ornithischian dinosaurs that lived from the Early Jurassic until the end of the Cretaceous.
Thyreophorans are characterized by the presence of bod ...
(heavy, quadrupedal thyreophorans)
::::::*†
Stegosauria
Stegosauria is a group of herbivorous ornithischian dinosaurs that lived during the Jurassic and early Cretaceous periods. Stegosaurian fossils have been found mostly in the Northern Hemisphere, predominantly in what is now North America, Europe, ...
(spikes and plates as primary armor)
:::::::*†
Huayangosauridae
Huayangosauridae (derived from ''Huayangosaurus'', " Huayang Guo Zhi reptile") is a family of stegosaurian dinosaurs from the Jurassic of China. The group is defined as all taxa closer to the namesake genus ''Huayangosaurus'' than ''Stegosaurus'', ...
(small stegosaurs with flank osteoderms and tail clubs)
:::::::*†
Stegosauridae
Stegosauridae is a family of thyreophoran dinosaurs (armoured dinosaurs) within the suborder Stegosauria. The clade is defined as all species of dinosaurs more closely related to ''Stegosaurus'' than ''Huayangosaurus''.David B. Weishampel, Peter ...
(large stegosaurs)
::::::*†
Ankylosauria
Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. ...
(
scute
A scute or scutum (Latin: ''scutum''; plural: ''scuta'' "shield") is a bony external plate or scale overlaid with horn, as on the shell of a turtle, the skin of crocodilians, and the feet of birds. The term is also used to describe the anterior po ...
s as primary armor)
:::::::*†
Parankylosauria
Parankylosauria is a group of basal ankylosaurian dinosaurs known from the Cretaceous of South America, Antarctica, and Australia. It is thought the group split from other ankylosaurs during the mid-Jurassic period, despite this being unpreserved ...
(small, southern ankylosaurs with
macuahuitl
A macuahuitl () is a weapon, a wooden club with several embedded obsidian blades. The name is derived from the Nahuatl language and means "hand-wood". Its sides are embedded with prismatic blades traditionally made from obsidian. Obsidian is ...
-like tails)
:::::::*†
Nodosauridae
Nodosauridae is a family of ankylosaurian dinosaurs, from the Late Jurassic to the Late Cretaceous period in what is now North America, South America, Europe, and Asia.
Description
Nodosaurids, like their close relatives the ankylosaurids, wer ...
(mostly spiky, club-less ankylosaurs)
:::::::*†
Ankylosauridae
Ankylosauridae () is a family of armored dinosaurs within Ankylosauria, and is the sister group to Nodosauridae. The oldest known Ankylosaurids date to around 122 million years ago and went extinct 66 million years ago during the Cretaceous–Pal ...
(characterized by flat scutes)
::::::::*†
Ankylosaurinae
Ankylosaurinae is a subfamily of ankylosaurid dinosaurs, existing from the Early Cretaceous about 105 million years ago until the end of the Late Cretaceous, about 66 mya. Many genera are included in the clade, such as ''Ankylosaurus'', ''Pinacos ...
(club-tailed ankylosaurids)
::::*†
Neornithischia
Neornithischia ("new ornithischians") is a clade of the dinosaur order Ornithischia. It is the sister group of the Thyreophora within the clade Genasauria. Neornithischians are united by having a thicker layer of asymmetrical enamel on the inside ...
("new ornithischians")
:::::*†
Cerapoda
Cerapoda ("ceratopsians" and "ornithopods") is a clade of the dinosaur order Ornithischia, that includes pachycephalosaurs, ceratopsians and ornithopods
Classification
Cerapoda is divided into two groups: Ornithopoda ("bird-foot") and Margin ...
("horned feet")
::::::*†
Marginocephalia
Marginocephalia (/mär′jə-nō-sə-făl′ē-ən/ Latin: margin-head) is a clade of ornithischian dinosaurs that is characterized by a bony shelf or margin at the back of the skull. These fringes were likely used for display. There are two clade ...
(characterized by a cranial growth)
:::::::*†
Pachycephalosauria
Pachycephalosauria (; from Greek παχυκεφαλόσαυρος for 'thick headed lizards') is a clade of ornithischian dinosaurs. Along with Ceratopsia, it makes up the clade Marginocephalia. With the exception of two species, most pachycephal ...
(bipeds with domed or knobby growth on skulls)
:::::::*†
Ceratopsia
Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. ...
(bipeds and quadrupeds; many had neck frills and horns)
::::::::*†
Chaoyangsauridae
Chaoyangsauridae is a family of ceratopsian dinosaurs. They are among the earliest known marginocephalian dinosaurs, with remains dating to about 160 million years ago, during the Late Jurassic period. Members of this group had sharp beaks for s ...
(small, frill-less basal ceratopsians)
::::::::*†
Neoceratopsia
Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. ...
("new ceratopsians")
:::::::::*†
Leptoceratopsidae
Leptoceratopsidae is an extinct family of neoceratopsian dinosaurs from Asia, North America and Europe. Leptoceratopsids resembled, and were closely related to, other neoceratopsians, such as the families Protoceratopsidae and Ceratopsidae, but t ...
(little to no frills, hornless, with robust jaws)
:::::::::*†
Protoceratopsidae
Protoceratopsidae is a family of basal (primitive) ceratopsians from the Late Cretaceous period. Although ceratopsians have been found all over the world, protoceratopsids are only definitively known from Cretaceous strata in Asia, with most spec ...
(basal ceratopsians with small frills and stubby horns)
::::::::::*†
Ceratopsoidea
Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. ...
(large-horned ceratopsians)
:::::::::::*†
Ceratopsidae
Ceratopsidae (sometimes spelled Ceratopidae) is a family of ceratopsian dinosaurs including ''Triceratops'', ''Centrosaurus'', and ''Styracosaurus''. All known species were quadrupedal herbivores from the Upper Cretaceous. All but one species are k ...
Chasmosaurinae
Chasmosaurinae is a subfamily of ceratopsid dinosaurs. They were one of the most successful groups of herbivores of their time. Chasmosaurines appeared in the early Campanian, and became extinct, along with all other non-avian dinosaurs, during ...
(ceratopsids with enlarged brow horns)
:::::::::::::*†
Triceratopsini
Triceratopsini is a tribe of herbivorous chasmosaurine dinosaurs that lived between the late Campanian to the late Maastrichtian stages of the Cretaceous period, between 74.73 and 66 million years ago. Fossils of these animals have been found in ...
(very large chasmosaurines with long brow horns)
::::::::::::*†
Centrosaurinae
Centrosaurinae (from the Greek, meaning "pointed lizards") is a subfamily of ceratopsid dinosaurs, a group of large quadrupedal ornithischians. Centrosaurine fossil remains are known primarily from the northern region of Laramidia (modern day Al ...
(ceratopsids mostly characterized by frill and nasal ornamentation)
:::::::::::::*†
Nasutoceratopsini
Centrosaurinae (from the Greek, meaning "pointed lizards") is a subfamily of ceratopsid dinosaurs, a group of large quadrupedal ornithischians. Centrosaurine fossil remains are known primarily from the northern region of Laramidia (modern day Al ...
(centrosaurines with enlarged nasal cavities)
:::::::::::::*†
Centrosaurini
Centrosaurinae (from the Greek language, Greek, meaning "pointed lizards") is a subfamily of ceratopsid dinosaurs, a group of large quadrupedal Ornithischia, ornithischians. Centrosaurine fossil remains are known primarily from the northern regio ...
(centrosaurines with enlarged nasal horns)
:::::::::::::*†
Pachyrhinosaurini
Pachyrhinosaurini is a tribe (biology), tribe of Centrosaurinae, centrosaurine dinosaurs. The clade existed during the Late Cretaceous, about 84.9 to 68.5 million years ago, evolving during the earliest Campanian, and becoming extinct i ...
(mostly had nasal bosses instead of horns)
::::::*†
Ornithopoda
Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (), that started out as small, bipedal running grazers and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world ...
(various sizes; bipeds and quadrupeds; evolved a method of chewing using skull flexibility and numerous teeth)
:::::::*†
Jeholosauridae
Jeholosaurids were herbivorous neornithischian dinosaurs from the Cretaceous Period (Aptian - Cenomanian). The family was first proposed by Han ''et al.'' in 2012. The jeholosaurids were defined as all neornithischians more closely related to ''J ...
(small Asian neornithischians)
:::::::*†
Thescelosauridae
Thescelosauridae is a clade of neornithischians from the Cretaceous of Asia, North America and possibly South America. The group was originally used as a name by Charles M. Sternberg in 1937, but was not formally defined until 2013, where it was ...
("wondrous lizards")
::::::::*†
Orodrominae
Orodrominae is a subfamily of thescelosaurid dinosaurs known from the Cretaceous of North America and Asia.
Distribution
Orodromines were a mostly North American based group with fossils from Canada and United States only. ''Albertadromeus'', as ...
(burrowers)
::::::::*†
Thescelosaurinae
Thescelosaurinae is a subfamily of thescelosaurid dinosaurs from the Early Cretaceous of Asia and the Late Cretaceous of North America.
Distribution
The distribution of Thescelosaurinae is quite large. They are widespread through United States a ...
(large thescelosaurids)
:::::::*†
Iguanodontia
Iguanodontia (the iguanodonts) is a clade of herbivorous dinosaurs that lived from the Middle Jurassic to Late Cretaceous. Some members include ''Camptosaurus'', ''Dryosaurus'', ''Iguanodon'', ''Tenontosaurus'', and the hadrosaurids or "duck-bi ...
("iguana teeth"; advanced ornithopods)
::::::::*†
Elasmaria
Elasmaria is a clade of ornithopods known from Cretaceous deposits in South America, Antarctica, and Australia that contains many bipedal ornithopods that were previously considered "hypsilophodonts".Madzia, Daniel; Boyd, Clint A.; Mazuch, Marti ...
(mostly southern ornithopods with mineralized plates along the ribs; may be thescelosaurids)
::::::::*†
Rhabdodontomorpha
Rhabdodontomorpha is a clade of basal iguanodont dinosaurs. This group was named in 2016 in the context of the description, based on Spanish findings of an early member of the Rhabdodontidae. A cladistic analysis was conducted in which it was fou ...
(with distinctive dentition)
:::::::::*†
Rhabdodontidae
Rhabdodontidae is a family of herbivorous iguanodontian ornithopod dinosaurs whose earliest stem members appeared in the middle of the Lower Cretaceous. The oldest dated fossils of these stem members were found in the Barremian Castrillo de la R ...
(European rhabdodontomorphs)
::::::::*†
Dryosauridae
Dryosaurids were primitive iguanodonts. They are known from Middle Jurassic to Early Cretaceous rocks of Africa, Europe, and North America.
Phylogeny
Until recently many dryosaurids have been regarded as dubious ('' Callovosaurus'' and '' Kan ...
(mid-sized, small headed)
::::::::*† Camptosauridae (mid-sized, stocky)
:::::::::*†
Styracosterna
Ankylopollexia is an extinct clade of ornithischian dinosaurs that lived from the Late Jurassic to the Late Cretaceous. It is a derived clade of iguanodontian ornithopods and contains the subgroup Styracosterna. The name stems from the Greek word ...
("spiked
sterna
''Sterna'' is a genus of terns in the bird family Laridae. The genus used to encompass most "white" terns indiscriminately, but mtDNA sequence comparisons have recently determined that this arrangement is paraphyletic. It is now restricted to t ...
")
::::::::::*†
Hadrosauriformes
Ankylopollexia is an extinct clade of ornithischian dinosaurs that lived from the Late Jurassic to the Late Cretaceous. It is a derived clade of iguanodontian ornithopods and contains the subgroup Styracosterna. The name stems from the Greek word ...
(ancestrally had a thumb spike)
:::::::::::*†
Hadrosauroidea
Hadrosauroidea is a clade or superfamily of ornithischian dinosaurs that includes the "duck-billed" dinosaurs, or hadrosaurids, and all dinosaurs more closely related to them than to ''Iguanodon''. Their remains have been recovered in Asia, Europ ...
(large quadrupedal herbivores, with teeth merged into dental batteries)
::::::::::::*†
Hadrosauromorpha
Hadrosauromorpha is a clade of iguanodontian ornithopods, defined in 2014 by David B. Norman to divide Hadrosauroidea into the basal taxa with compressed manual bones and a pollex, and the derived taxa that lack them. The clade is defined as a ...
(hadrosaurids and their closest relatives)
:::::::::::::*†
Hadrosauridae
Hadrosaurids (), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod family, which includ ...
("duck-billed dinosaurs"; often with crests)
::::::::::::::*†
Saurolophinae
Saurolophinae is a subfamily of hadrosaurid dinosaurs. It has since the mid-20th century generally been called the Hadrosaurinae, a group of largely non-crested hadrosaurs related to the crested sub-family Lambeosaurinae. However, the name Hadro ...
(hadrosaurids with solid, small, no crests)
:::::::::::::::*†
Brachylophosaurini
Brachylophosaurini is a tribe of saurolophine hadrosaurs with known material being from N. America and potentially Asia. It contains at least four taxa; ''Acristavus'' (from Montana and Utah), ''Brachylophosaurus'' (from Montana and Alberta), '' ...
(short-crested)
:::::::::::::::*†
Kritosaurini
Kritosaurini is a tribe of saurolophine hadrosaurid dinosaurs from the Late Cretaceous.
Discovery and naming
The first member of the group discovered and named was ''Kritosaurus''; it was named by paleontologist Barnum Brown in 1910. Four year ...
(enlarged, solid nasal crests)
:::::::::::::::*†
Saurolophini
Saurolophini is a tribe of saurolophine hadrosaurids native to the Americas and Asia. It includes ''Saurolophus'' (from Canada and Mongolia), ''Augustynolophus'' (from the United States), and ''Prosaurolophus'' (from Alberta, Canada, and Montana, ...
(small, spike-like crests)
:::::::::::::::*†
Edmontosaurini
Edmontosaurini are a tribe of saurolophine hadrosaur dinosaurs that lived in the Northern Hemisphere during the Late Cretaceous period. It currently contains '' Edmontosaurus'' (from Canada and the United States), '' Shantungosaurus'' and '' La ...
(flat-headed saurolophines)
::::::::::::::*†
Lambeosaurinae
Lambeosaurinae is a group of crested hadrosaurid dinosaurs.
Classification
Lambeosaurines have been traditionally split into the tribes or clades Parasaurolophini (''Parasaurolophus'', ''Charonosaurus'', others (?).) and Lambeosaurini (''Coryt ...
(hadrosaurids often with hollow crests)
:::::::::::::::*†
Aralosaurini
Aralosaurini is a proposed tribe of hadrosaurid dinosaurs belonging to the subfamily Lambeosaurinae. The members of this group lived in Asia and Europe during the end of the Late Cretaceous about 83.6 to 66.0 million years ago. The clade may not be ...
(solid-crested)
:::::::::::::::*†
Tsintaosaurini
Tsintaosaurini is a tribe of basal lambeosaurine hadrosaurs native to Eurasia. It is thought to contains the genera ''Tsintaosaurus'' (from China), ''Pararhabdodon'' (from Spain) and '' Koutalisaurus'' (also from Spain), though some studies have ...
(vertical, tube-like crests)
:::::::::::::::*†
Parasaurolophini
Parasaurolophini is a tribe of derived corythosaurian lambeosaurine hadrosaurids that are native to Asia, and North America. It is defined as everything closer to ''Parasaurolophus walkeri'' than to ''Lambeosaurus lambei''. It currently contain ...
(long, backwards-arcing crests)
:::::::::::::::*†
Lambeosaurini
Lambeosaurini, previously known as Corythosaurini, is one of four tribes of hadrosaurid ornithopods from the family Lambeosaurinae. It is defined as all lambeosaurines closer to ''Lambeosaurus lambei'' than to ''Parasaurolophus walkeri, Tsintaosau ...
(usually rounded crests)
:*
Saurischia
Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...
::*†
Herrerasauridae
Herrerasauridae is a family of carnivorous dinosaurs, possibly basal to either theropods or even all of saurischians, or even their own branching from dracohors, separate from dinosauria altogether. They are among the oldest known dinosaurs, fi ...
(early bipedal carnivores)
::*†
Sauropodomorpha
Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lon ...
(herbivores with small heads, long necks, and long tails)
:::*†
Unaysauridae
Unaysauridae is a clade of basal sauropodomorphs from the Late Triassic of India and Brazil.
Diagnosis and systematics
Unaysauridae was defined by Müller ''et al.'' (2018) as the most inclusive clade including ''Unaysaurus tolentinoi'', but no ...
Plateosauria
Plateosauria is a clade of sauropodomorph dinosaurs which lived during the Late Triassic to the Late Cretaceous. The name Plateosauria was first coined by Gustav Tornier in 1913. The name afterwards fell out of use until the 1980s.
Classificat ...
(diverse; bipeds and quadrupeds)
::::*†
Massospondylidae
Massospondylidae is a family of early massopod dinosaurs that existed in Asia, Africa, North America, South America and AntarcticaHellert, Spencer M. "A New Basal Sauropodomorph from The Early Jurassic Hanson Formation of Antarctica." Geologica ...
(long-necked, primitive sauropodomorphs)
::::*†
Riojasauridae
Riojasauridae is an extinct family of sauropodomorph dinosaurs from the Late Triassic Period (late Carnian to Norian Ages). It contains the genera '' Riojasaurus'' and '' Eucnemesaurus''. The Riojasauridae is considered a stem taxon, and is defi ...
(large, primitive sauropodomorphs)
:::::*†
Sauropodiformes
Massopoda is a clade of sauropodomorph dinosaurs which lived during the Late Triassic to Late Cretaceous epochs. It was named by paleontologist Adam M. Yates of the University of the Witwatersrand in 2007. Massopoda is a stem-based taxon, define ...
(heavy, bipeds and quadrupeds)
::::::*†
Sauropoda
Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their bo ...
(very large and heavy; quadrupedal)
:::::::*†
Lessemsauridae
Lessemsauridae is a clade of early sauropodiform dinosaurs that lived in the Triassic and Jurassic of Argentina, South Africa and possibly Lesotho. A phylogenetic analysis performed by Apaldetti and colleagues in 2018 recovered a new clade of sa ...
(gigantic yet lacking several weight-saving adaptations)
:::::::*†
Gravisauria
Gravisauria is a clade of sauropod dinosaurs consisting of some genera, Vulcanodontidae and Eusauropoda.Allain, R. and Aquesbi, N. (2008). "Anatomy and phylogenetic relationships of ''Tazoudasaurus naimi'' (Dinosauria, Sauropoda) from the late Ea ...
("heavy lizards")
::::::::*†
Eusauropoda
Eusauropoda (meaning "true sauropods") is a derived clade of sauropod dinosaurs. Eusauropods represent the node-based group that includes all descendant sauropods starting with the basal eusauropods of ''Shunosaurus'', and possibly ''Barapasaur ...
("true sauropods")
:::::::::*†
Turiasauria
Turiasauria is an unranked clade of basal sauropod dinosaurs known from Middle Jurassic to Early Cretaceous deposits in Europe, North America, and Africa.
Description
Turiasauria was originally erected by Royo-Torres et al. (2006) to include '' ...
(often large, widespread sauropods)
:::::::::*†
Neosauropoda
Neosauropoda is a clade within Dinosauria, coined in 1986 by Argentine paleontologist José Bonaparte and currently described as ''Saltasaurus loricatus'', ''Diplodocus longus'', and all animals directly descended from their most recent common ...
("new sauropods"; columnar limbs)
::::::::::*†
Diplodocoidea
Diplodocoidea is a superfamily of sauropod dinosaurs, which included some of the longest animals of all time, including slender giants like ''Supersaurus'', ''Diplodocus'', ''Apatosaurus'', and ''Amphicoelias''. Most had very long necks and long, ...
(skulls and tails elongated; teeth typically narrow and pencil-like)
:::::::::::*†
Rebbachisauridae
Rebbachisauridae is a family of sauropod dinosaurs known from fragmentary fossil remains from the Cretaceous of South America, Africa, North America, Europe and possibly Central Asia.
Taxonomy
In 1990 sauropod specialist Jack McIntosh included t ...
(short-necked, low-browsing diplodocoids often with high backs)
:::::::::::*†
Flagellicaudata
Flagellicaudata is a clade of Dinosauria. It belongs to Sauropoda and includes two families, the Dicraeosauridae and the Diplodocidae.
Phylogeny
The clade Flagellicaudata was erected by Harris and Dodson (2004) for the diplodocoid clade formed ...
(whip-tailed)
::::::::::::*†
Dicraeosauridae
Dicraeosauridae is a family of diplodocoid sauropods who are the sister group to Diplodocidae. Dicraeosaurids are a part of the Flagellicaudata, along with Diplodocidae. Dicraeosauridae includes genera such as ''Amargasaurus'', ''Suuwassea'', ''D ...
(small, short-necked diplodocoids with enlarged cervical and dorsal vertebrae)
::::::::::::*†
Diplodocidae
Diplodocids, or members of the family Diplodocidae ("double beams"), are a group of sauropod dinosaurs. The family includes some of the longest creatures ever to walk the Earth, including ''Diplodocus'' and '' Supersaurus'', some of which may hav ...
(extremely long-necked)
:::::::::::::*†
Apatosaurinae
Apatosaurinae is a subfamily of diplodocid sauropods that existed between 157 and 150 million years ago in North America. The group includes two genera for certain, ''Apatosaurus'' and ''Brontosaurus'', and at least five species. ''Atlantosaurus ...
(robust cervical vertebrae)
:::::::::::::*†
Diplodocinae
Diplodocinae is an extinct subfamily of diplodocid sauropods that existed from the Late Jurassic to Early Cretaceous of North America, Europe, Africa and South America, about 161.2 to 136.4 million years ago. Genera within the subfamily include ...
(long, thin necks)
::::::::::*†
Macronaria
Macronaria is a clade of sauropod dinosaurs. Macronarians are named after the large diameter of the nasal opening of their skull, known as the external naris, which exceeded the size of the orbit, the skull opening where the eye is located (hence ...
(boxy skulls; spoon- or pencil-shaped teeth)
:::::::::::*†
Titanosauriformes
Macronaria is a clade of sauropod dinosaurs. Macronarians are named after the large diameter of the nasal opening of their skull, known as the external naris, which exceeded the size of the orbit, the skull opening where the eye is located (hence ...
("titan lizard forms")
::::::::::::*†
Brachiosauridae
The Brachiosauridae ("arm lizards", from Greek ''brachion'' (βραχίων) = "arm" and ''sauros'' = "lizard") are a family or clade of herbivorous, quadrupedal sauropod dinosaurs. Brachiosaurids had long necks that enabled them to access the ...
Somphospondyli
Somphospondyli is an extinct clade of titanosauriform sauropods that lived from the Late Jurassic until the end of the Late Cretaceous, comprising all titanosauriforms more closely related to Titanosauria proper than Brachiosauridae. The remains ...
("porous vertebrae")
:::::::::::::*†
Euhelopodidae
Euhelopodidae is a family of sauropod dinosaurs of disputed membership and affinities, which contains ''Euhelopus'' and its close relatives. Most proposed euhelopodids are from East Asia.
Euhelopodidae was first recognized by Carl Wiman in 1929, ...
(stocky, mostly Asian)
:::::::::::::*†
Titanosauria
Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still thr ...
(diverse; stocky, with wide hips; most common in the Late Cretaceous of southern continents)
::*
Theropoda
Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally ca ...
(carnivorous)
:::*†
Neotheropoda
Neotheropoda (meaning "new theropods") is a clade that includes coelophysoids and more advanced theropod dinosaurs, and is the only group of theropods that survived the Triassic–Jurassic extinction event. All neotheropods became extinct by the e ...
("new theropods")
::::*†
Coelophysoidea
Coelophysoidea were common dinosaurs of the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivorous forms with a superficial similarity to the ...
(early theropods; includes ''
Coelophysis
''Coelophysis'' ( traditionally; or , as heard more commonly in recent decades) is an extinct genus of coelophysid theropod dinosaur that lived approximately 228 to 201.3 million years ago during the latter part of the Triassic Period from t ...
'' and close relatives)
::::*†"Dilophosaur-grade neotheropods" (larger kink-snouted dinosaurs)
::::*
Averostra
Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs, namely Ceratosauria and Tetanurae, and represent the only group of post-Early Jurassic theropods. Both survived into the Cretaceous period. When the Cretaceous–Paleo ...
("bird snouts")
:::::*†
Ceratosauria
Ceratosaurs are members of the clade Ceratosauria, a group of dinosaurs defined as all theropods sharing a more recent common ancestor with ''Ceratosaurus'' than with birds. The oldest known ceratosaur, ''Saltriovenator'', dates to the earliest ...
(generally elaborately horned carnivores that existed from the Jurassic to Cretaceous periods, originally included Coelophysoidea)
::::::*†
Ceratosauridae
Ceratosauridae is an extinct family of theropod dinosaurs belonging to the infraorder Ceratosauria. The family's type genus, ''Ceratosaurus'', was first found in Jurassic rocks from North America. Ceratosauridae is made up of the genera ''Cerat ...
(ceratosaurs with large teeth)
::::::*†
Abelisauroidea
Abelisauroidea is typically regarded as a Cretaceous group, though the earliest abelisauridae remains are known from the Middle Jurassic of Argentina (classified as the species Eoabelisaurus mefi) and possibly Madagascar (fragmentary remains of ...
(ceratosaurs exemplified by reduced arms and hands)
:::::::*†
Abelisauridae
Abelisauridae (meaning "Abel's lizards") is a family (or clade) of ceratosaurian theropod dinosaurs. Abelisaurids thrived during the Cretaceous period, on the ancient southern supercontinent of Gondwana, and today their fossil remains are found ...
(large abelisauroids with short arms and oftentimes elaborate facial ornamentation)
:::::::*†
Noasauridae
Noasauridae is an extinct family of theropod dinosaurs belonging to the group Ceratosauria. They were closely related to the short-armed abelisaurids, although most noasaurids had much more traditional body types generally similar to other ther ...
(diverse, generally light theropods; may include several obscure taxa)
::::::::*† Elaphrosaurinae (bird-like; omnivorous as juveniles but herbivorous as adults)
::::::::*†
Noasaurinae
Noasauridae is an extinct family of theropod dinosaurs belonging to the group Ceratosauria. They were closely related to the short-armed abelisaurids, although most noasaurids had much more traditional body types generally similar to other ther ...
(small carnivores)
:::::*
Tetanurae
Tetanurae (/ˌtɛtəˈnjuːriː/ or "stiff tails") is a clade that includes most theropod dinosaurs, including megalosauroids, allosauroids, tyrannosauroids, ornithomimosaurs, compsognathids and maniraptorans (including birds). Tetanurans are ...
(stiff-tailed dinosaurs)
::::::*†
Megalosauroidea
Megalosauroidea (meaning 'great/big lizard forms') is a superfamily (or clade) of tetanuran theropod dinosaurs that lived from the Middle Jurassic to the Late Cretaceous period. The group is defined as ''Megalosaurus bucklandii'' and all taxa sha ...
(early group of large carnivores)
:::::::*†
Piatnitzkysauridae
Piatnitzkysauridae is an extinct family of megalosauroid or basal Allosauroid dinosaurs. It only consists of three known dinosaur genera: '' Condorraptor'', ''Marshosaurus'', and ''Piatnitzkysaurus.'' The most complete and well known member of t ...
(small basal megalosauroids endemic to the Americas)
:::::::*†
Megalosauridae
Megalosauridae is a monophyletic family of carnivorous theropod dinosaurs within the group Megalosauroidea. Appearing in the Middle Jurassic, megalosaurids were among the first major radiation of large theropod dinosaurs. They were a relatively ...
(large megalosauroids with powerful arms and hands)
:::::::*†
Spinosauridae
The Spinosauridae (or spinosaurids) are a clade or family of tetanuran theropod dinosaurs comprising ten to seventeen known genera. They came into prominence during the Cretaceous period. Spinosaurid fossils have been recovered worldwide, includin ...
(crocodile-like, semiaquatic carnivores)
::::::*†
Avetheropoda
Avetheropoda, or "bird theropods", is a clade that includes carnosaurians and coelurosaurs to the exclusion of other dinosaurs.
Definition
Avetheropoda was named by Gregory S. Paul in 1988, and was first defined as a clade by Currie and Padian i ...
("bird theropods")
:::::::*†
Megaraptora
Megaraptora is a clade of carnivorous Tetanurae, tetanuran theropod dinosaurs with controversial relations to other theropods. Its Derived (phylogenetics), derived members, the Megaraptoridae are noted for their elongated hand claws and proporti ...
(theropods with large hand claws; either carnosaurs or coelurosaurs, potentially tyrannosauroids)
:::::::*†
Carnosauria
Carnosauria is an extinct large group of predatory dinosaurs that lived during the Jurassic and Cretaceous periods. Starting from the 1990s, scientists have discovered some very large carnosaurs in the carcharodontosaurid family, such as ''Gig ...
(large meat-eating dinosaurs; megalosauroids sometimes included)
::::::::*†
Metriacanthosauridae
Metriacanthosauridae is an extinct family of allosauroid theropod dinosaurs that lived from the Middle Jurassic to the Early Cretaceous. When broken down into its Greek roots, it means "moderately-spined lizards". The family is split into two sub ...
(primitive Asian allosauroids)
::::::::*†
Allosauridae
Allosauridae is a family of medium to large bipedal, carnivorous allosauroid theropod dinosaurs from the Late Jurassic. Allosauridae is a fairly old taxonomic group, having been first named by the American paleontologist Othniel Charles Marsh in ...
(''
Allosaurus
''Allosaurus'' () is a genus of large carnosaurian theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic epoch (Kimmeridgian to late Tithonian). The name "''Allosaurus''" means "different lizard" alluding to ...
'' and its very closest relatives)
::::::::*†
Carcharodontosauria
Allosauroidea is a superfamily or clade of theropod dinosaurs which contains four families — the Metriacanthosauridae, Allosauridae, Carcharodontosauridae, and Neovenatoridae. Allosauroids, alongside the family Megalosauroidea, were among t ...
(robust allosauroids)
:::::::::*†
Carcharodontosauridae
Carcharodontosauridae (carcharodontosaurids; from the Greek καρχαροδοντόσαυρος, ''carcharodontósauros'': "shark-toothed lizards") is a group of carnivorous theropod dinosaurs. In 1931, Ernst Stromer named Carcharodontosauridae ...
(includes some of the largest purely terrestrial carnivores)
:::::::::*†
Neovenatoridae
Neovenatoridae is a proposed clade of carcharodontosaurian dinosaurs uniting some primitive members of the group such as ''Neovenator'' with the Megaraptora, a group of theropods with controversial affinities. Other studies recover megaraptorans ...
("new hunters"; may include megaraptorans)
:::::::*
Coelurosauria
Coelurosauria (; from Greek, meaning "hollow tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs.
Coelurosauria is a subgroup of theropod dinosaurs that includes compsognathids, tyrann ...
(feathered theropods, with a range of body sizes and niches)
::::::::*†"Nexus of basal coelurosaurs" (used by Tweet to denote well-known taxa with unstable positions at the base of Coelurosauria)
::::::::*†
Tyrannoraptora
Tyrannoraptora is a clade defined as "all descendants of the last common ancestor of ''Tyrannosaurus rex'' and ''Passer domesticus'' (the house sparrow)". The clade was named in 1999 by the American paleontologist Paul Sereno, though in his origi ...
("tyrant thieves")
:::::::::*†
Compsognathidae
Compsognathidae is a family of coelurosaurian theropod dinosaurs. Compsognathids were small carnivores, generally conservative in form, hailing from the Jurassic and Cretaceous Periods. The bird-like features of these species, along with other d ...
(small early coelurosaurs with short forelimbs)
:::::::::*†
Tyrannosauroidea
Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent b ...
Proceratosauridae
Proceratosauridae is a Family (biology), family or clade of Tyrannosauroidea, tyrannosauroid theropod dinosaurs from the Middle Jurassic to the Early Cretaceous.
Distinguishing features
Unlike the advanced Tyrannosauridae, tyrannosaurids but s ...
(tyrannosauroids with head crests)
::::::::::*†
Tyrannosauridae
Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to thirteen genera, including the eponymous ''Tyrannosaurus''. The exact number of genera ...
(''
Tyrannosaurus
''Tyrannosaurus'' is a genus of large theropoda, theropod dinosaur. The species ''Tyrannosaurus rex'' (''rex'' meaning "king" in Latin), often called ''T. rex'' or colloquially ''T-Rex'', is one of the best represented theropods. ''Tyrannosa ...
'' and close relatives)
:::::::::*†
Maniraptoriformes
Maniraptoriformes is a clade of dinosaurs with pennaceous feathers and wings that contains ornithomimosaurs and maniraptorans. This group was named by Thomas Holtz, who defined it as "the most recent common ancestor of '' Ornithomimus'' and bird ...
(bird-like dinosaurs)
::::::::::*†
Ornithomimosauria
Ornithomimosauria ("bird-mimic lizards") are theropod dinosaurs which bore a superficial resemblance to the modern-day ostrich. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period (geology), Period of Laurasia (now Asia ...
(small-headed, mostly toothless, omnivorous or possible herbivores)
:::::::::::*†
Ornithomimidae
Ornithomimidae (meaning "bird-mimics") is a family of theropod dinosaurs which bore a superficial resemblance to modern ostriches. Ornithomimids were fast, omnivorous or herbivorous dinosaurs known mainly from the Late Cretaceous Period of Lauras ...
(very ostrich-like dinosaurs)
::::::::::*
Maniraptora
Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to ''Ornithomimus velox''. It contains the major subgroups Avialae, Deinonychosauria, Oviraptoros ...
(dinosaurs with pennaceous feathers)
:::::::::::*†
Alvarezsauroidea
Alvarezsauroidea is a group of small maniraptoran dinosaurs. Alvarezsauroidea, Alvarezsauridae, and Alvarezsauria are named for the historian Gregorio Álvarez, not the more familiar physicist Luis Alvarez, or his son geologist Walter Alvarez ...
(small hunters with reduced forelimbs)
::::::::::::*†
Alvarezsauridae
Alvarezsauridae is a family of small, long-legged dinosaurs. Although originally thought to represent the earliest known flightless birds, they are now thought to be an early diverging branch of maniraptoran theropods. Alvarezsaurids were highly ...
(insectivores with only one enlarged digit)
:::::::::::*†
Therizinosauria
Therizinosaurs (once called segnosaurs) were large herbivorous theropod dinosaurs whose fossils have been found across the Early to Late Cretaceous deposits in Asia and North America. Various features of the forelimbs, skull and pelvis unite the ...
(tall, long-necked theropods; omnivores and herbivores)
::::::::::::*†
Therizinosauroidea
Therizinosaurs (once called segnosaurs) were large herbivorous theropod dinosaurs whose fossils have been found across the Early to Late Cretaceous deposits in Asia and North America. Various features of the forelimbs, skull and pelvis unite thes ...
(larger therizinosaurs)
:::::::::::::*†Therizinosauridae (sloth-like herbivores, often with enlarged claws)
:::::::::::*†Oviraptorosauria (omnivorous, beaked dinosaurs)
::::::::::::*†Caudipteridae (bird-like, basal oviraptorosaurs)
::::::::::::*†Caenagnathoidea (cassowary-like oviraptorosaurs)
:::::::::::::*†Caenagnathidae (toothless oviraptorosaurs known from North America and Asia)
:::::::::::::*†Oviraptoridae (characterized by two bony projections at the back of the mouth; exclusive to Asia)
:::::::::::*Paraves (avialans and their closest relatives)
::::::::::::*†Scansoriopterygidae (small tree-climbing theropods with membranous wings)
::::::::::::*†Deinonychosauria (toe-clawed dinosaurs; may not form a natural group)
:::::::::::::*†Archaeopterygidae (small, winged theropods or primitive birds)
:::::::::::::*†Troodontidae (omnivores; enlarged brain cavities)
:::::::::::::*†Dromaeosauridae ("raptors")
::::::::::::::*†Microraptoria (characterized by large wings on both the arms and legs; may have been capable of powered flight)
::::::::::::::*†Eudromaeosauria (hunters with greatly enlarged sickle claws)
:::::::::::::*†Unenlagiidae (piscivores; may be dromaeosaurids)
::::::::::::::*†Halszkaraptorinae (duck-like; potentially semiaquatic)
::::::::::::::*†Unenlagiinae (long-snouted)
::::::::::::*Avialae (modern birds and extinct relatives)
Triassic
The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
from: -199.6 till: -145.5 color:jurassic text:
Jurassic
The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
from: -145.5 till: -65.5 color:cretaceous text:
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
from: -65.5 till: -23.03 color:paleogene text:
Paleogene
The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...
Herrerasauridae
Herrerasauridae is a family of carnivorous dinosaurs, possibly basal to either theropods or even all of saurischians, or even their own branching from dracohors, separate from dinosauria altogether. They are among the oldest known dinosaurs, fi ...
Riojasauridae
Riojasauridae is an extinct family of sauropodomorph dinosaurs from the Late Triassic Period (late Carnian to Norian Ages). It contains the genera '' Riojasaurus'' and '' Eucnemesaurus''. The Riojasauridae is considered a stem taxon, and is defi ...
Turiasauria
Turiasauria is an unranked clade of basal sauropod dinosaurs known from Middle Jurassic to Early Cretaceous deposits in Europe, North America, and Africa.
Description
Turiasauria was originally erected by Royo-Torres et al. (2006) to include '' ...
Diplodocoidea
Diplodocoidea is a superfamily of sauropod dinosaurs, which included some of the longest animals of all time, including slender giants like ''Supersaurus'', ''Diplodocus'', ''Apatosaurus'', and ''Amphicoelias''. Most had very long necks and long, ...
color:pur bar:NAM10 from:-157 till:-93 text:
Brachiosauridae
The Brachiosauridae ("arm lizards", from Greek ''brachion'' (βραχίων) = "arm" and ''sauros'' = "lizard") are a family or clade of herbivorous, quadrupedal sauropod dinosaurs. Brachiosaurids had long necks that enabled them to access the ...
color:pur bar:NAM11 from:-140 till:-66 text:
Titanosauria
Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still thr ...
color:ther bar:NAM12 from:-221 till:-183 text:
Coelophysoidea
Coelophysoidea were common dinosaurs of the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivorous forms with a superficial similarity to the ...
color:ther bar:NAM13 from:-199.3 till:-66 text:
Ceratosauria
Ceratosaurs are members of the clade Ceratosauria, a group of dinosaurs defined as all theropods sharing a more recent common ancestor with ''Ceratosaurus'' than with birds. The oldest known ceratosaur, ''Saltriovenator'', dates to the earliest ...
color:ther bar:NAM14 from:-170 till:-85 text:
Megalosauroidea
Megalosauroidea (meaning 'great/big lizard forms') is a superfamily (or clade) of tetanuran theropod dinosaurs that lived from the Middle Jurassic to the Late Cretaceous period. The group is defined as ''Megalosaurus bucklandii'' and all taxa sha ...
color:ther bar:NAM15 from:-175.6 till:-88 text:
Carnosauria
Carnosauria is an extinct large group of predatory dinosaurs that lived during the Jurassic and Cretaceous periods. Starting from the 1990s, scientists have discovered some very large carnosaurs in the carcharodontosaurid family, such as ''Gig ...
color:ther bar:NAM16 from:-130 till:-66 text:
Megaraptora
Megaraptora is a clade of carnivorous Tetanurae, tetanuran theropod dinosaurs with controversial relations to other theropods. Its Derived (phylogenetics), derived members, the Megaraptoridae are noted for their elongated hand claws and proporti ...
color:ther bar:NAM17 from:-166 till:-66 text:
Tyrannosauroidea
Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent b ...
color:ther bar:NAM18 from:-151.5 till:-108 text:
Compsognathidae
Compsognathidae is a family of coelurosaurian theropod dinosaurs. Compsognathids were small carnivores, generally conservative in form, hailing from the Jurassic and Cretaceous Periods. The bird-like features of these species, along with other d ...
color:ther bar:NAM19 from:-140 till:-66 text:
Ornithomimosauria
Ornithomimosauria ("bird-mimic lizards") are theropod dinosaurs which bore a superficial resemblance to the modern-day ostrich. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period (geology), Period of Laurasia (now Asia ...
Therizinosauria
Therizinosaurs (once called segnosaurs) were large herbivorous theropod dinosaurs whose fossils have been found across the Early to Late Cretaceous deposits in Asia and North America. Various features of the forelimbs, skull and pelvis unite the ...
Heterodontosauridae
Heterodontosauridae is a family of ornithischian dinosaurs that were likely among the most basal (primitive) members of the group. Their phylogenetic placement is uncertain but they are most commonly found to be primitive, outside of the group ...
color:orn bar:NAM26 from:-169 till:-100 text:
Stegosauria
Stegosauria is a group of herbivorous ornithischian dinosaurs that lived during the Jurassic and early Cretaceous periods. Stegosaurian fossils have been found mostly in the Northern Hemisphere, predominantly in what is now North America, Europe, ...
color:orn bar:NAM27 from:-170.3 till:-66 text:
Ankylosauria
Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. ...
color:orn bar:NAM28 from:-92 till:-66 text:
Pachycephalosauria
Pachycephalosauria (; from Greek παχυκεφαλόσαυρος for 'thick headed lizards') is a clade of ornithischian dinosaurs. Along with Ceratopsia, it makes up the clade Marginocephalia. With the exception of two species, most pachycephal ...
color:orn bar:NAM29 from:-161 till:-66 text:
Ceratopsia
Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. ...
color:orn bar:NAM30 from:-164 till:-66 text:
Ornithopoda
Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (), that started out as small, bipedal running grazers and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world ...
Triassic
The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
from: -199.6 till: -145.5 color:jurassic text:
Jurassic
The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
from: -145.5 till: -65.5 color:cretaceous text:
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
from: -65.5 till: -23.03 color:paleogene text:
Paleogene
The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...
Knowledge about dinosaurs is derived from a variety of fossil and non-fossil records, including fossilized bones, feces, Fossil trackway, trackways, gastroliths, feathers, impressions of skin, Organ (anatomy), internal organs and other soft tissues. Many fields of study contribute to our understanding of dinosaurs, including physics (especially biomechanics), chemistry, biology, and the Earth sciences (of which paleontology is a sub-discipline). Two topics of particular interest and study have been dinosaur size and behavior.
Size
Current evidence suggests that dinosaur average size varied through the Triassic, Early Jurassic, Late Jurassic and Cretaceous. Predatory theropod dinosaurs, which occupied most terrestrial carnivore niches during the Mesozoic, most often fall into the category when sorted by estimated weight into categories based on order of magnitude, whereas Holocene, recent predatory carnivoran mammals peak in the category. The Mode (statistics), mode of Mesozoic dinosaur body masses is between . This contrasts sharply with the average size of Cenozoic mammals, estimated by the National Museum of Natural History as about .
The sauropods were the largest and heaviest dinosaurs. For much of the dinosaur era, the smallest sauropods were larger than anything else in their habitat, and the largest was an order of magnitude more massive than anything else that has since walked the Earth. Giant prehistoric mammals such as ''Paraceratherium'' (the largest land mammal ever) were dwarfed by the giant sauropods, and only modern whales approach or surpass them in size. There are several proposed advantages for the large size of sauropods, including protection from predation, reduction of energy use, and longevity, but it may be that the most important advantage was dietary. Large animals are more efficient at digestion than small animals, because food spends more time in their digestive systems. This also permits them to subsist on food with lower nutritive value than smaller animals. Sauropod remains are mostly found in rock formations interpreted as dry or seasonally dry, and the ability to eat large quantities of low-nutrient browse would have been advantageous in such environments.
Largest and smallest
Scientists will probably never be certain of the largest organisms, largest and smallest dinosaurs to have ever existed. This is because only a tiny percentage of animals were ever fossilized and most of these remain buried in the earth. Few of the specimens that are recovered are complete skeletons, and impressions of skin and other soft tissues are rare. Rebuilding a complete skeleton by comparing the size and morphology of bones to those of similar, better-known species is an inexact art, and reconstructing the muscles and other organs of the living animal is, at best, a process of educated guesswork.
The tallest and heaviest dinosaur known from good skeletons is ''Giraffatitan, Giraffatitan brancai'' (previously classified as a species of ''Brachiosaurus''). Its remains were discovered in Tanzania between 1907 and 1912. Bones from several similar-sized individuals were incorporated into the skeleton now mounted and on display at the Natural History Museum, Berlin, Museum für Naturkunde in Berlin; this mount is tall and long, and would have belonged to an animal that weighed between and kilograms ( and lb). The longest complete dinosaur is the long ''Diplodocus'', which was discovered in Wyoming in the United States and displayed in Pittsburgh's Carnegie Museum of Natural History in 1907. The longest dinosaur known from good fossil material is the ''Patagotitan'': the skeleton mount in the
American Museum of Natural History
The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 inter ...
in New York City, New York is long. The Museo Carmen Funes, Museo Municipal Carmen Funes in Plaza Huincul, Argentina, has an ''Argentinosaurus'' reconstructed skeleton mount that is long.
There were larger dinosaurs, but knowledge of them is based entirely on a small number of fragmentary fossils. Most of the largest herbivorous specimens on record were discovered in the 1970s or later, and include the massive ''Argentinosaurus'', which may have weighed to kilograms (90 to 110 short tons) and reached lengths of ; some of the longest were the long ''Diplodocus hallorum'' (formerly ''Seismosaurus''), the long ''Supersaurus'', and long ''Patagotitan''; and the tallest, the tall ''Sauroposeidon'', which could have reached a sixth-floor window. The heaviest and longest dinosaur may have been ''Maraapunisaurus'', known only from a now lost partial vertebral Vertebra#Structure, neural arch described in 1878. Extrapolating from the illustration of this bone, the animal may have been long and weighed kg ( lb). However, as no further evidence of sauropods of this size has been found, and the discoverer, Cope, had made typographic errors before, it is likely to have been an extreme overestimation.
The largest carnivorous dinosaur was ''Spinosaurus'', reaching a length of , and weighing . Other large carnivorous theropods included ''Giganotosaurus'', ''Carcharodontosaurus'' and ''
Tyrannosaurus
''Tyrannosaurus'' is a genus of large theropoda, theropod dinosaur. The species ''Tyrannosaurus rex'' (''rex'' meaning "king" in Latin), often called ''T. rex'' or colloquially ''T-Rex'', is one of the best represented theropods. ''Tyrannosa ...
''. ''Therizinosaurus'' and ''Deinocheirus'' were among the tallest of the theropods. The largest ornithischian dinosaur was probably the hadrosaurid ''Shantungosaurus, Shantungosaurus giganteus'' which measured . The largest individuals may have weighed as much as .
The smallest dinosaur known is the bee hummingbird, with a length of only and mass of around . The smallest known non-Avialae, avialan dinosaurs were about the size of pigeons and were those theropods most closely related to birds. For example, ''Anchiornis huxleyi'' is currently the smallest non-avialan dinosaur described from an adult specimen, with an estimated weight of and a total skeletal length of . The smallest herbivorous non-avialan dinosaurs included ''Microceratus'' and ''Wannanosaurus'', at about long each.
Behavior
Many modern birds are highly social, often found living in flocks. There is general agreement that some behaviors that are common in birds, as well as in crocodiles (closest living relatives of birds), were also common among extinct dinosaur groups. Interpretations of behavior in fossil species are generally based on the pose of skeletons and their Habitat (ecology), habitat, computer simulations of their biomechanics, and comparisons with modern animals in similar ecological niches.
The first potential evidence for herding or flocking (behavior), flocking as a widespread behavior common to many dinosaur groups in addition to birds was the 1878 discovery of 31 ''Iguanodon'', ornithischians that were then thought to have perished together in Bernissart, Belgium, after they fell into a deep, flooded sinkhole and drowned. Other mass-death sites have been discovered subsequently. Those, along with multiple trackways, suggest that gregarious behavior was common in many early dinosaur species. Trackways of hundreds or even thousands of herbivores indicate that duck-billed (hadrosaurids) may have moved in great herds, like the American bison or the African Springbok. Sauropod tracks document that these animals traveled in groups composed of several different species, at least in Oxfordshire, England, although there is no evidence for specific herd structures. Congregating into herds may have evolved for defense, for Bird migration, migratory purposes, or to provide protection for young. There is evidence that many types of slow-growing dinosaurs, including various theropods, sauropods, ankylosaurians, ornithopods, and ceratopsians, formed aggregations of immature individuals. One example is a site in Inner Mongolia that has yielded remains of over 20 ''Sinornithomimus'', from one to seven years old. This assemblage is interpreted as a social group that was trapped in mud. The interpretation of dinosaurs as gregarious has also extended to depicting carnivorous theropods as pack hunters working together to bring down large prey. However, this lifestyle is uncommon among modern birds, crocodiles, and other reptiles, and the taphonomy, taphonomic evidence suggesting mammal-like pack hunting in such theropods as ''Deinonychus'' and ''
Allosaurus
''Allosaurus'' () is a genus of large carnosaurian theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic epoch (Kimmeridgian to late Tithonian). The name "''Allosaurus''" means "different lizard" alluding to ...
'' can also be interpreted as the results of fatal disputes between feeding animals, as is seen in many modern diapsid predators.
The crests and frills of some dinosaurs, like the marginocephalians, theropods and Lambeosaurinae, lambeosaurines, may have been too fragile to be used for active defense, and so they were likely used for sexual or aggressive displays, though little is known about dinosaur mating and territory (animal), territorialism. Head wounds from bites suggest that theropods, at least, engaged in active aggressive confrontations.
From a behavioral standpoint, one of the most valuable dinosaur fossils was discovered in the Gobi Desert in 1971. It included a ''Velociraptor'' attacking a ''Protoceratops'', providing evidence that dinosaurs did indeed attack each other. Additional evidence for attacking live prey is the partially healed tail of an ''Edmontosaurus'', a hadrosaurid dinosaur; the tail is damaged in such a way that shows the animal was bitten by a tyrannosaur but survived. Cannibalism (zoology), Cannibalism amongst some species of dinosaurs was confirmed by tooth marks found in Madagascar in 2003, involving the theropod ''Majungasaurus''.
Comparisons between the sclerotic ring, scleral rings of dinosaurs and modern birds and reptiles have been used to infer daily activity patterns of dinosaurs. Although it has been suggested that most dinosaurs were active during the day, these comparisons have shown that small predatory dinosaurs such as dromaeosaurids, ''Juravenator'', and ''Megapnosaurus'' were likely nocturnal. Large and medium-sized herbivorous and omnivorous dinosaurs such as ceratopsians, sauropodomorphs, hadrosaurids, ornithomimosaurs may have been cathemeral, active during short intervals throughout the day, although the small ornithischian ''Agilisaurus'' was inferred to be Diurnality, diurnal.
Based on fossil evidence from dinosaurs such as ''Oryctodromeus'', some ornithischian species seem to have led a partially fossorial (burrowing) lifestyle. Many modern birds are arboreal (tree climbing), and this was also true of many Mesozoic birds, especially the enantiornithines. While some early bird-like species may have already been arboreal as well (including dromaeosaurids) such as ''Microraptor'') most non-avialan dinosaurs seem to have relied on land-based locomotion. A good understanding of how dinosaurs moved on the ground is key to models of dinosaur behavior; the science of biomechanics, pioneered by Robert McNeill Alexander, has provided significant insight in this area. For example, studies of the forces exerted by muscles and gravity on dinosaurs' skeletal structure have investigated how fast dinosaurs could run, whether diplodocids could create sonic booms via whip-like tail snapping, and whether sauropods could float.
Communication
Modern birds are known to Animal communication, communicate using visual and auditory signals, and the wide diversity of visual display structures among fossil dinosaur groups, such as horns, frills, crests, sails, and feathers, suggests that visual communication has always been important in dinosaur biology. Reconstruction of the plumage color of ''Anchiornis'', suggest the importance of color in visual communication in non-avian dinosaurs. The evolution of dinosaur vocalization is less certain. Paleontologist Phil Senter has suggested that non-avian dinosaurs relied mostly on visual displays and possibly non-vocal acoustic sounds like hissing, jaw grinding or clapping, splashing and wing beating (possible in winged maniraptoran dinosaurs). He states they were unlikely to have been capable of vocalizing since their closest relatives, crocodilians and birds, use different means to vocalize, the former via the larynx and the latter through the unique Syrinx (bird anatomy), syrinx, suggesting they evolved independently and their common ancestor was mute.
The earliest remains of a syrinx, which has enough mineral content for fossilization, was found in a specimen of the duck-like ''Vegavis, Vegavis iaai'' dated 69 –66 million years ago, and this organ is unlikely to have existed in non-avian dinosaurs. However, in contrast to Senter, other researchers have suggested that dinosaurs could vocalize and that the syrinx-based vocal system of birds evolved from a larynx-based one, rather than the two systems evolving independently. A 2016 study suggests that some dinosaurs produced closed mouth vocalizations like cooing, hooting and booming. These occur in both reptiles and birds and involve inflating the esophagus or tracheal pouches. Such vocalizations evolved independently in extant archosaurs numerous times, following increases in body size. The crests of the
Lambeosaurini
Lambeosaurini, previously known as Corythosaurini, is one of four tribes of hadrosaurid ornithopods from the family Lambeosaurinae. It is defined as all lambeosaurines closer to ''Lambeosaurus lambei'' than to ''Parasaurolophus walkeri, Tsintaosau ...
and nasal chambers of ankylosaurids have been suggested to have functioned in vocal resonance, though Senter stated that the presence of resonance chambers in some dinosaurs is not necessarily evidence of vocalization as modern snakes have such chambers which intensify their hisses.
Reproductive biology
All dinosaurs laid Amniote, amniotic eggs. Dinosaur eggs were usually laid in a nest. Most species create somewhat elaborate nests which can be cups, domes, plates, beds scrapes, mounds, or burrows. Some species of modern bird have no nests; the cliff-nesting Common murre, common guillemot lays its eggs on bare rock, and male emperor penguins keep eggs between their body and feet. Primitive birds and many non-avialan dinosaurs often lay eggs in communal nests, with males primarily incubating the eggs. While modern birds have only one functional oviduct and lay one egg at a time, more primitive birds and dinosaurs had two oviducts, like crocodiles. Some non-avialan dinosaurs, such as ''Troodon'', exhibited iterative laying, where the adult might lay a pair of eggs every one or two days, and then ensured simultaneous hatching by delaying Broodiness#Broodiness in non-avian animals, brooding until all eggs were laid.
When laying eggs, females grow a special type of bone between the hard outer bone and the Bone marrow, marrow of their limbs. This medullary bone, which is rich in calcium, is used to make eggshells. A discovery of features in a ''Tyrannosaurus'' skeleton provided evidence of medullary bone in extinct dinosaurs and, for the first time, allowed paleontologists to establish the sex of a fossil dinosaur specimen. Further research has found medullary bone in the carnosaur ''Allosaurus'' and the ornithopod ''Tenontosaurus''. Because the line of dinosaurs that includes ''Allosaurus'' and ''Tyrannosaurus'' diverged from the line that led to ''Tenontosaurus'' very early in the evolution of dinosaurs, this suggests that the production of medullary tissue is a general characteristic of all dinosaurs.
Another widespread trait among modern birds (but see below in regards to fossil groups and extant megapodes) is parental care for young after hatching. Jack Horner (paleontologist), Jack Horner's 1978 discovery of a ''Maiasaura'' ("good mother lizard") nesting ground in Montana demonstrated that parental care continued long after birth among ornithopods. A specimen of the oviraptoridae, oviraptorid ''Citipati, Citipati osmolskae'' was discovered in a Chicken#Broodiness, chicken-like brooding position in 1993, which may indicate that they had begun using an insulating layer of feathers to keep the eggs warm. An embryo of the basal sauropodomorph ''Massospondylus'' was found without teeth, indicating that some parental care was required to feed the young dinosaurs. Trackways have also confirmed parental behavior among ornithopods from the Isle of Skye in northwestern Scotland.
However, there is ample evidence of precociality or Precociality#Superprecociality, superprecociality among many dinosaur species, particularly theropods. For instance, non-Euornithes, ornithuromorph birds have been abundantly demonstrated to have had slow growth rates, megapode-like egg burying behavior and the ability to fly soon after birth. Both ''Tyrannosaurus'' and ''Troodon'' had juveniles with clear superprecociality and likely occupying different ecological niches than the adults. Superprecociality has been inferred for sauropods.
Genital structures are unlikely to fossilize as they lack scales that may allow preservation via pigmentation or residual calcium phosphate salts. In 2021, the best preserved specimen of a dinosaur's cloacal vent exterior was described for ''Psittacosaurus'', demonstrating lateral swellings similar to crocodylian musk glands used in social displays by both sexes and pigmented regions which could also reflect a signalling function. However, this specimen on its own does not offer enough information to determine whether this dinosaur had sexual signalling functions; it only supports the possibility. Cloacal visual signalling can occur in either males or females in living birds, making it unlikely to be useful to determine sex for extinct dinosaurs.
Physiology
Because both modern crocodilians and birds have four-chambered hearts (albeit modified in crocodilians), it is likely that this is a trait shared by all archosaurs, including all dinosaurs. While all modern birds have high metabolisms and are endothermic ("warm-blooded"), a vigorous debate has been ongoing since the 1960s regarding how far back in the dinosaur lineage this trait extended. Various researchers have supported dinosaurs as being endothermic, ectothermic ("cold-blooded"), or somewhere in between. An emerging consensus among researchers is that, while different lineages of dinosaurs would have had different metabolisms, most of them had higher metabolic rates than other reptiles but lower than living birds and mammals, which is termed mesothermy by some. Evidence from crocodiles and their extinct relatives suggests that such elevated metabolisms could have developed in the earliest archosaurs, which were the common ancestors of dinosaurs and crocodiles.
After non-avian dinosaurs were discovered, paleontologists first posited that they were ectothermic. This was used to imply that the ancient dinosaurs were relatively slow, sluggish organisms, even though many modern reptiles are fast and light-footed despite relying on external sources of heat to regulate their body temperature. The idea of dinosaurs as ectothermic remained a prevalent view until Robert T. Bakker, an early proponent of dinosaur endothermy, published an influential paper on the topic in 1968. Bakker specifically used anatomical and ecological evidence to argue that sauropods, which had hitherto been depicted as sprawling aquatic animals with their tails dragging on the ground, were endotherms that lived vigorous, terrestrial lives. In 1972, Bakker expanded on his arguments based on energy requirements and predator-prey ratios. This was one of the seminal results that led to the Dinosaur renaissance.
One of the greatest contributions to the modern understanding of dinosaur physiology has been histology, paleohistology, the study of microscopic tissue structure in dinosaurs. From the 1960s forward, Armand de Ricqlès suggested that the presence of fibrolamellar bone—bony tissue with an irregular, fibrous texture and filled with blood vessels—was indicative of consistently fast growth and therefore endothermy. Fibrolamellar bone was common in both dinosaurs and pterosaurs, though not universally present. This has led to a significant body of work in reconstructing growth curve (biology), growth curves and modeling the evolution of growth rates across various dinosaur lineages,For examples of this work conducted on different dinosaur lineages, see
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* which has suggested overall that dinosaurs grew faster than living reptiles. Other lines of evidence suggesting endothermy include the presence of feathers and other types of body coverings in many lineages (see ); more consistent ratios of the isotope oxygen-18 in bony tissue compared to ectotherms, particularly as latitude and thus air temperature varied, which suggests stable internal temperatures (although these ratios can be altered during fossilization); and the discovery of South Polar region of the Cretaceous#Dinosaurs, polar dinosaurs, which lived in Australia, Antarctica, and Alaska when these places would have had cool, temperate climates.
In saurischian dinosaurs, higher metabolisms were supported by the evolution of the avian respiratory system, characterized by an extensive system of air sacs that extended the lungs and invaded many of the bones in the skeleton, making them hollow. Such respiratory systems, which may have appeared in the earliest saurischians, would have provided them with more oxygen compared to a mammal of similar size, while also having a larger resting tidal volume and requiring a lower breathing frequency, which would have allowed them to sustain higher activity levels. The rapid airflow would also have been an effective cooling mechanism, which in conjunction with a lower metabolic rate would have prevented large sauropods from overheating. These traits may have enabled sauropods to grow quickly to gigantic sizes. Sauropods may also have benefitted from their size—their small surface area to volume ratio meant that they would have been able to thermoregulate more easily, a phenomenon termed gigantothermy.
Like other reptiles, dinosaurs are primarily uricotelic, that is, their kidneys extract nitrogenous wastes from their bloodstream and excrete it as uric acid instead of urea or ammonia via the ureters into the intestine. This would have helped them to conserve water. In most living species, uric acid is excreted along with feces as a semisolid waste. However, at least some modern birds (such as hummingbirds) can be facultatively ammonotelic, excreting most of the nitrogenous wastes as ammonia. This material, as well as the output of the intestines, emerges from the cloaca. In addition, many species regurgitate Pellet (ornithology), pellets, and fossil pellets are known as early as the Jurassic from ''Anchiornis''.
The size and shape of the brain can be partly reconstructed based on the surrounding bones. In 1896, Marsh calculated ratios between brain weight and body weight of seven species of dinosaurs, showing that the brain of dinosaurs was proportionally smaller than in today's crocodiles, and that the brain of ''Stegosaurus'' was smaller than in any living land vertebrate. This contributed to the widespread public notion of dinosaurs as being sluggish and extraordinarily stupid. Harry Jerison, in 1973, showed that proportionally smaller brains are expected at larger body sizes, and that brain size in dinosaurs was not smaller than expected when compared to living reptiles. Later research showed that relative brain size progressively increased during the evolution of theropods, with the highest intelligence – comparable to that of modern birds – calculated for the troodontid ''Troodon''.
Origin of birds
The possibility that dinosaurs were the ancestors of birds was first suggested in 1868 by Thomas Henry Huxley. After the work of Gerhard Heilmann in the early 20th century, the Scientific theory, theory of birds as dinosaur descendants was abandoned in favor of the idea of them being descendants of generalized Thecodontia, thecodonts, with the key piece of evidence being the supposed lack of clavicles in dinosaurs. However, as later discoveries showed, clavicles (or a single fused furcula, wishbone, which derived from separate clavicles) were not actually absent; they had been found as early as 1924 in ''Oviraptor'', but misidentified as an interclavicle. In the 1970s, Ostrom revived the dinosaur–bird theory, which gained momentum in the coming decades with the advent of cladistic analysis, and a great increase in the discovery of small theropods and early birds. Of particular note have been the fossils of the Yixian Formation, where a variety of theropods and early birds have been found, often with feathers of some type. Birds share over a hundred distinct anatomical features with theropod dinosaurs, which are now generally accepted to have been their closest ancient relatives. They are most closely allied with maniraptoran coelurosaurs. A minority of scientists, most notably Alan Feduccia and Larry Martin, have proposed other evolutionary paths, including revised versions of Heilmann's basal archosaur proposal, or that maniraptoran theropods are the ancestors of birds but themselves are not dinosaurs, only convergent evolution, convergent with dinosaurs.
Feathers
Feathers are one of the most recognizable characteristics of modern birds, and a trait that was also shared by several non-avian dinosaurs. Based on the current distribution of fossil evidence, it appears that feathers were an ancestral dinosaurian trait, though one that may have been selectively lost in some species. Direct fossil evidence of feathers or feather-like structures has been discovered in a diverse array of species in many non-avian dinosaur groups, both among saurischians and ornithischians. Simple, branched, feather-like structures are known from Heterodontosauridae, heterodontosaurids, primitive neornithischians, and theropods, and primitive ceratopsians. Evidence for true, vaned feathers similar to the flight feathers of modern birds has been found only in the theropod subgroup Maniraptora, which includes oviraptorosaurs, troodontids, dromaeosaurids, and birds. Feather-like structures known as Pterosaur#Pycnofibers, pycnofibres have also been found in pterosaurs, suggesting the possibility that feather-like filaments may have been common in the bird lineage and evolved before the appearance of dinosaurs themselves. Research into the genetics of American alligators has also revealed that crocodylian
scute
A scute or scutum (Latin: ''scutum''; plural: ''scuta'' "shield") is a bony external plate or scale overlaid with horn, as on the shell of a turtle, the skin of crocodilians, and the feet of birds. The term is also used to describe the anterior po ...
s do possess feather-keratins during embryonic development, but these keratins are not expressed by the animals before hatching.
''Archaeopteryx'' was the first fossil found that revealed a potential connection between dinosaurs and birds. It is considered a transitional fossil, in that it displays features of both groups. Brought to light just two years after Charles Darwin's seminal ''On the Origin of Species'' (1859), its discovery spurred the nascent debate between proponents of evolutionary biology and creationism. This early bird is so dinosaur-like that, without a clear impression of feathers in the surrounding rock, at least one specimen was mistaken for the small theropod ''Compsognathus''. Since the 1990s, a number of additional feathered dinosaurs have been found, providing even stronger evidence of the close relationship between dinosaurs and modern birds. Most of these specimens were unearthed in the Lagerstätten, lagerstätte of the Yixian Formation, Liaoning, northeastern China, which was part of an island continent during the Cretaceous. Though feathers have been found in only a few locations, it is possible that non-avian dinosaurs elsewhere in the world were also feathered. The lack of widespread fossil evidence for feathered non-avian dinosaurs may be because delicate features like skin and feathers are seldom preserved by fossilization and thus often absent from the fossil record.
The description of feathered dinosaurs has not been without controversy; perhaps the most vocal critics have been Alan Feduccia and Theagarten Lingham-Soliar, who have proposed that some purported feather-like fossils are the result of the decomposition of collagenous fiber that underlaid the dinosaurs' skin, and that maniraptoran dinosaurs with vaned feathers were not actually dinosaurs, but convergent with dinosaurs. However, their views have for the most part not been accepted by other researchers, to the point that the scientific nature of Feduccia's proposals has been questioned.
Skeleton
Because feathers are often associated with birds, feathered dinosaurs are often touted as the missing link between birds and dinosaurs. However, the multiple skeletal features also shared by the two groups represent another important line of evidence for paleontologists. Areas of the skeleton with important similarities include the neck, pubis, wrist (semi-lunate carpal), arm and Shoulder girdle, pectoral girdle, furcula (wishbone), and Keel (bird anatomy), breast bone. Comparison of bird and dinosaur skeletons through cladistic analysis strengthens the case for the link.
Soft anatomy
Large meat-eating dinosaurs had a complex system of air sacs similar to those found in modern birds, according to a 2005 investigation led by Patrick M. O'Connor. The lungs of theropod dinosaurs (carnivores that walked on two legs and had bird-like feet) likely pumped air into hollow sacs in their skeletons, as is the case in birds. "What was once formally considered unique to birds was present in some form in the ancestors of birds", O'Connor said. In 2008, scientists described ''Aerosteon, Aerosteon riocoloradensis'', the skeleton of which supplies the strongest evidence to date of a dinosaur with a bird-like breathing system. CT scanning of ''Aerosteons fossil bones revealed evidence for the existence of air sacs within the animal's body cavity.
Behavioral evidence
Fossils of the troodonts ''Mei long, Mei'' and ''Sinornithoides'' demonstrate that some dinosaurs slept with their heads tucked under their arms. This behavior, which may have helped to keep the head warm, is also characteristic of modern birds. Several Deinonychosauria, deinonychosaur and oviraptorosaur specimens have also been found preserved on top of their nests, likely brooding in a bird-like manner. The ratio between egg volume and body mass of adults among these dinosaurs suggest that the eggs were primarily brooded by the male, and that the young were highly precocial, similar to many modern ground-dwelling birds.
Some dinosaurs are known to have used gizzard stones like modern birds. These stones are swallowed by animals to aid digestion and break down food and hard fibers once they enter the stomach. When found in association with fossils, gizzard stones are called gastroliths.
Extinction of major groups
All non-avian dinosaurs and most lineages of birds became extinct in a extinction event, mass extinction event, called the Cretaceous–Paleogene extinction event, Cretaceous–Paleogene (K-Pg) extinction event, at the end of the Cretaceous period. Above the Cretaceous–Paleogene boundary, which has been dated to 66.038 ± 0.025 million years ago, fossils of non-avian dinosaurs disappear abruptly; the absence of dinosaur fossils was historically used to assign rocks to the ensuing
Cenozoic
The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...
. The nature of the event that caused this mass extinction has been extensively studied since the 1970s, leading to the development of two mechanisms that are thought to have played major roles: an extraterrestrial impact event in the Yucatán Peninsula, along with flood basalt volcanism in India. However, the specific mechanisms of the extinction event and the extent of its effects on dinosaurs are still areas of ongoing research. Alongside dinosaurs, many other groups of animals became extinct: pterosaurs, marine reptiles such as mosasaurs and plesiosaurs, several groups of mammals, ammonoidea, ammonites (nautilus-like Mollusca, mollusks), rudists (reef-building bivalvia, bivalves), and various groups of marine plankton. In all, approximately 47% of genera and 76% of species on Earth became extinct during the K-Pg extinction event. The relatively large size of most dinosaurs and the low diversity of small-bodied dinosaur species at the end of the Cretaceous may have contributed to their extinction; the extinction of the bird lineages that did not survive may also have been caused by a dependence on forest habitats or a lack of adaptations to seed predation, eating seeds for survival.
Pre-extinction diversity
Just before the K-Pg extinction event, the number of non-avian dinosaur species that existed globally has been estimated at between 628 and 1078. It remains uncertain whether the diversity of dinosaurs was in gradual decline before the K-Pg extinction event, or whether dinosaurs were actually thriving prior to the extinction. Rock formations from the Maastrichtian epoch, which directly preceded the extinction, have been found to have lower diversity than the preceding Campanian epoch, which led to the prevailing view of a long-term decline in diversity. However, these comparisons did not account either for varying preservation potential between rock units or for different extents of exploration and excavation. In 1984, Dale Russell carried out an analysis to account for these biases, and found no evidence of a decline; another analysis by David Fastovsky and colleagues in 2004 even showed that dinosaur diversity continually increased until the extinction, but this analysis has been rebutted. Since then, different approaches based on statistics and mathematical models have variously supported either a sudden extinction or a gradual decline. End-Cretaceous trends in diversity may have varied between dinosaur lineages: it has been suggested that sauropods were not in decline, while ornithischians and theropods were in decline.
Impact event
The Alvarez hypothesis, bolide impact hypothesis, first brought to wide attention in 1980 by Walter Alvarez, Luis Walter Alvarez, Luis Alvarez, and colleagues, attributes the K-Pg extinction event to a bolide (extraterrestrial projectile) impact. Alvarez and colleagues proposed that a sudden increase in iridium levels, recorded around the world in rock deposits at the Cretaceous–Paleogene boundary, was direct evidence of the impact. Shocked quartz, indicative of a strong shockwave emanating from an impact, was also found worldwide. The actual impact site remained elusive until a Chicxulub crater, crater measuring wide was discovered in the Yucatán Peninsula of southeastern Mexico, and was publicized in a 1991 paper by Alan R. Hildebrand, Alan Hildebrand and colleagues. Now, the bulk of the evidence suggests that a bolide wide impacted the Yucatán Peninsula 66 million years ago, forming this crater and creating a "kill mechanism" that triggered the extinction event.
Within hours, the Chicxulub impact would have created immediate effects such as earthquakes, tsunamis, and a global firestorm that likely killed unsheltered animals and started wildfires. However, it would also have had longer-term consequences for the environment. Within days, sulphate aerosols released from rocks at the impact site would have contributed to acid rain and ocean acidification. Soot aerosols are thought to have spread around the world over the ensuing months and years; they would have cooled the surface of the Earth by reflecting thermal radiation, and greatly slowed photosynthesis by blocking out sunlight, thus creating an impact winter. (This role was ascribed to sulphate aerosols until experiments demonstrated otherwise.) The cessation of photosynthesis would have led to the collapse of food webs depending on leafy plants, which included all dinosaurs save for grain-eating birds.
Deccan Traps
At the time of the K-Pg extinction, the Deccan Traps flood basalts of India were actively erupting. The eruptions can be separated into three phases around the K-Pg boundary, two prior to the boundary and one after. The second phase, which occurred very close to the boundary, would have extruded 70 to 80% of the volume of these eruptions in intermittent pulses that occurred around 100,000 years apart. Greenhouse gases such as carbon dioxide and sulphur dioxide would have been released by this volcanic activity, resulting in climate change through temperature perturbations of roughly but possibly as high as . Like the Chicxulub impact, the eruptions may also have released sulphate aerosols, which would have caused acid rain and global cooling. However, due to large error margins in the dating of the eruptions, the role of the Deccan Traps in the K-Pg extinction remains unclear.
Before 2000, arguments that the Deccan Traps eruptions—as opposed to the Chicxulub impact—caused the extinction were usually linked to the view that the extinction was gradual. Prior to the discovery of the Chicxulub crater, the Deccan Traps were used to explain the global iridium layer; even after the crater's discovery, the impact was still thought to only have had a regional, not global, effect on the extinction event. In response, Luis Alvarez rejected volcanic activity as an explanation for the iridium layer and the extinction as a whole. Since then, however, most researchers have adopted a more moderate position, which identifies the Chicxulub impact as the primary progenitor of the extinction while also recognizing that the Deccan Traps may also have played a role. Walter Alvarez himself has acknowledged that the Deccan Traps and other ecological factors may have contributed to the extinctions in addition to the Chicxulub impact. Some estimates have placed the start of the second phase in the Deccan Traps eruptions within 50,000 years after the Chicxulub impact. Combined with mathematical modelling of the seismic waves that would have been generated by the impact, this has led to the suggestion that the Chicxulub impact may have triggered these eruptions by increasing the permeability of the mantle plume underlying the Deccan Traps.
Whether the Deccan Traps were a major cause of the extinction, on par with the Chicxulub impact, remains uncertain. Proponents consider the climatic impact of the sulphur dioxide released to have been on par with the Chicxulub impact, and also note the role of flood basalt volcanism in other mass extinctions like the Permian-Triassic extinction event. They consider the Chicxulub impact to have worsened the ongoing climate change caused by the eruptions. Meanwhile, detractors point out the sudden nature of the extinction and that other pulses in Deccan Traps activity of comparable magnitude did not appear to have caused extinctions. They also contend that the causes of different mass extinctions should be assessed separately. In 2020, Alfio Chiarenza and colleagues suggested that the Deccan Traps may even have had the opposite effect: they suggested that the long-term warming caused by its carbon dioxide emissions may have dampened the impact winter from the Chicxulub impact.
Possible Paleocene survivors
Non-avian dinosaur remains have occasionally been found above the K-Pg boundary. In 2000, Spencer G. Lucas, Spencer Lucas and colleagues reported the discovery of a single hadrosaur right femur in the San Juan Basin of New Mexico, and described it as evidence of Paleocene dinosaurs. The rock unit in which the bone was discovered has been dated to the early Paleocene epoch, approximately 64.8 million years ago. If the bone was not deposition (geology), re-deposited by weathering action, it would provide evidence that some dinosaur populations may have survived at least half a million years into the Cenozoic. Other evidence includes the presence of dinosaur remains in the Hell Creek Formation up to above the Cretaceous–Paleogene boundary, representing 40,000 years of elapsed time. This has been used to support the view that the K-Pg extinction was gradual. However, these supposed Paleocene dinosaurs are considered by many other researchers to be reworked fossil, reworked, that is, washed out of their original locations and then re-buried in younger sediments. The age estimates have also been considered unreliable.
Cultural depictions
By human standards, dinosaurs were creatures of fantastic appearance and often enormous size. As such, they have captured the popular imagination and become an enduring part of human culture. The entry of the word "dinosaur" into the common vernacular reflects the animals' cultural importance: in English, "dinosaur" is commonly used to describe anything that is impractically large, obsolete, or bound for extinction.
Public enthusiasm for dinosaurs first developed in Victorian era, Victorian England, where in 1854, three decades after the first scientific descriptions of dinosaur remains, a menagerie of lifelike Crystal Palace dinosaurs, dinosaur sculptures was unveiled in London's Crystal Palace Park. The Crystal Palace dinosaurs proved so popular that a strong market in smaller replicas soon developed. In subsequent decades, dinosaur exhibits opened at parks and Natural history museum, museums around the world, ensuring that successive generations would be introduced to the animals in an immersive and exciting way. The enduring popularity of dinosaurs, in its turn, has resulted in significant public funding for dinosaur science, and has frequently spurred new discoveries. In the United States, for example, the competition between museums for public attention led directly to the Bone Wars of the 1880s and 1890s, during which a pair of feuding paleontologists made enormous scientific contributions.
The popular preoccupation with dinosaurs has ensured their appearance in literature, film, and other Media (communication), media. Beginning in 1852 with a passing mention in Charles Dickens ''Bleak House'', dinosaurs have been featured in large numbers of fictional works. Jules Verne's 1864 novel ''Journey to the Center of the Earth'', Arthur Conan Doyle, Sir Arthur Conan Doyle's 1912 book ''The Lost World (Doyle novel), The Lost World'', the 1914 animated film ''Gertie the Dinosaur'' (featuring the first animated dinosaur), the iconic 1933 motion picture, film ''King Kong (1933 film), King Kong'', the 1954 ''Godzilla (1954 film), Godzilla'' and its many sequels, the best-selling 1990 novel ''Jurassic Park (novel), Jurassic Park'' by Michael Crichton and its 1993 Jurassic Park (film), film adaptation are just a few notable examples of dinosaur appearances in fiction. Authors of general-interest non-fiction works about dinosaurs, including some prominent paleontologists, have often sought to use the animals as a way to educate readers about science in general. Dinosaurs are ubiquitous in advertising; numerous Company (law), companies have referenced dinosaurs in printed or televised advertisements, either in order to sell their own products or in order to characterize their rivals as slow-moving, dim-witted, or obsolete.
See also
* Dinosaur diet and feeding
* Evolutionary history of life
* Lists of dinosaur-bearing stratigraphic units
* List of dinosaur genera
* List of bird genera
* List of birds
* List of informally named dinosaurs
Further reading
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Notes
Bibliography
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* The 5th edition of the book is available from th Internet Archive Retrieved 2019-10-19.
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* "Reprint of papers published in a special volume of Modern geology [v. 18 (Halstead memorial volume), 1993], with five additional contributions.--Pref."
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References
{{DEFAULTSORT:Dinosaur
Carnian first appearances
Dinosaurs,
Extant Late Triassic first appearances
Fossil taxa described in 1842
Taxa named by Richard Owen