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Tyrannosauroidea (meaning 'tyrant lizard forms') is a
superfamily SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid sequences into known structural domains, especially into SCOP superfamilies. Domains are functional, str ...
(or
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, ...
) of
coelurosaur 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 ...
ian
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 ...
dinosaur 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 ...
s that includes the
family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
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 ...
as well as more basal relatives. Tyrannosauroids lived on the
Laurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pan ...
n
supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continent, continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", ...
beginning in 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 ...
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 ...
. By the end of the
Cretaceous Period 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 t ...
, tyrannosauroids were the dominant large predators in the
Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...
, culminating in the gigantic ''
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 ...
''.
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 ...
s of tyrannosauroids have been recovered on what are now the continents of North America, Europe and Asia, with fragmentary remains possibly attributable to tyrannosaurs also known from South America and Australia. Tyrannosauroids were
biped 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' a ...
al
carnivore 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 ...
s, as were most theropods, and were characterized by numerous skeletal features, especially of 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 ...
and
pelvis 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 ...
. Early in their existence, tyrannosauroids were small predators with long, three-fingered forelimbs.
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 ...
genera became much larger, including some of the largest land-based predators ever to exist, but most of these later genera had proportionately small forelimbs with only two digits. Primitive
feather Feathers are epidermal growths that form a distinctive outer covering, or plumage, on both avian (bird) and some non-avian dinosaurs and other archosaurs. They are the most complex integumentary structures found in vertebrates and a premier ...
s have been identified in fossils of two species and may have been present in other tyrannosauroids as well. Prominent bony crests in a variety of shapes and sizes on the skulls of many tyrannosauroids may have served
display Display may refer to: Technology * Display device, output device for presenting information, including: ** Cathode ray tube, video display that provides a quality picture, but can be very heavy and deep ** Electronic visual display, output devi ...
functions.


Description

Tyrannosauroids varied widely in size, although there was a general trend towards increasing size over time. Early tyrannosauroids were small animals. One specimen of ''Dilong'', almost fully grown, measured 1.6 meters (5.3 ft) in length, and a fully grown ''
Guanlong ''Guanlong'' (冠龍) is a genus of extinct proceratosaurid tyrannosauroid from the Late Jurassic of China. The taxon was first described in 2006 by Xu Xing ''et al.'', who found it to represent a new taxon related to ''Tyrannosaurus''. The na ...
'' measured 3 meters (10 ft long). Teeth from lower Lower Cretaceous rocks (140 to 136 million years old) of Hyogo,
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
, appear to have come from an approximately long animal, possibly indicating an early size increase in the lineage. An immature ''
Eotyrannus ''Eotyrannus'' (meaning "dawn tyrant") is a genus of tyrannosauroid theropod dinosaur hailing from the Early Cretaceous Wessex Formation beds, included in Wealden Group, located in the southwest coast of the Isle of Wight, United Kingdom. The rem ...
'' was over 4 meters (13 ft) in length, and a subadult ''
Appalachiosaurus ''Appalachiosaurus'' ( ; "Appalachian lizard") is a genus of tyrannosauroid theropod dinosaur from the Late Cretaceous Period of eastern North America. Like almost all theropods, it was a bipedal predator. Only a juvenile skeleton has been found ...
'' was estimated at more than 6 meters (20 ft) long, indicating that both genera reached larger sizes. The Late Cretaceous tyrannosaurids ranged from the 9 meter (30 ft) ''
Albertosaurus ''Albertosaurus'' (; meaning "Alberta lizard") is a genus of tyrannosaurid theropod dinosaurs that lived in western North America during the Late Cretaceous Period, about 71 million years ago. The type species, ''A. sarcophagus'', was app ...
'' and ''
Gorgosaurus ''Gorgosaurus'' ( ; ) is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period (Campanian), between about 76.6 and 75.1 million years ago. Fossil remains have been found in the Can ...
'' to ''Tyrannosaurus'', which exceeded 12 meters (39 ft) in length and may have weighed more than 6,400 
kilogram The kilogram (also kilogramme) is the unit of mass in the International System of Units (SI), having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo colloquially ...
s (7 
short ton The short ton (symbol tn) is a measurement unit equal to . It is commonly used in the United States, where it is known simply as a ton, although the term is ambiguous, the single word being variously used for short, long, and metric ton. The vari ...
s). A 2010 review of the literature concluded that tyrannosaurs were "small- to mid-sized" for their first 80 million years but were "some of the largest terrestrial carnivores to ever live" in their last 20 million years. Skulls of early tyrannosauroids were long, low and lightly constructed, similar to other coelurosaurs, while later forms had taller and more massive skulls. Despite the differences in form, certain skull features are found in all known tyrannosauroids. The
premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...
ry bone is very tall, blunting the front of the snout, a feature which evolved convergently in
abelisaurid 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 ...
s. The
nasal bone The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose. Eac ...
s are characteristically fused, arched slightly upwards and often very roughly textured on their upper surface. The premaxillary teeth at the front of the upper jaw are shaped differently from the rest of the teeth, smaller in size and with a ''D''-shaped
cross section Cross section may refer to: * Cross section (geometry) ** Cross-sectional views in architecture & engineering 3D *Cross section (geology) * Cross section (electronics) * Radar cross section, measure of detectability * Cross section (physics) **Abs ...
. In the
lower jaw In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
, a prominent ridge on the surangular bone extends sideways from just below the jaw joint, except in the basal ''Guanlong''. Tyrannosauroids had ''S''-shaped necks and long tails, as did most other theropods. Early genera had long forelimbs, about 60% the length of the hindlimb in ''Guanlong'', with the typical three digits of coelurosaurs. The long forelimb persisted at least through the Early Cretaceous ''Eotyrannus'', but is unknown in ''Appalachiosaurus''.
Derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...
tyrannosaurids have forelimbs strongly reduced in size, the most extreme example being ''
Tarbosaurus ''Tarbosaurus'' ( ; meaning "alarming lizard") is a genus of tyrannosaurid dinosaur that flourished in Asia about 70 million years ago, at the end of the Late Cretaceous Period, considered to contain a single known species, ''Tarbosaurus bataa ...
'' from
Mongolia Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million, ...
, where 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 ...
was only one-quarter the length of 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 ...
. The third digit of the forelimb was also reduced over time. This digit was unreduced in the basal ''Guanlong'', while in ''Dilong'' it was more slender than the other two digits. ''Eotyrannus'' also had three functional digits on each hand. Tyrannosaurids had only two, although the
vestigial Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...
metacarpal In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones ...
of the third are preserved in some well-preserved specimens. bstract only/ref> As in most coelurosaurs, the second digit of the hand is the largest, even when the third digit is not present. Characteristic features of the tyrannosauroid pelvis include a
concave Concave or concavity may refer to: Science and technology * Concave lens * Concave mirror Mathematics * Concave function, the negative of a convex function * Concave polygon, a polygon which is not convex * Concave set * The concavity In ca ...
notch at the upper front end of the ilium, a sharply defined vertical ridge on the outside surface of the ilium, extending upwards from the
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 ...
(hip socket), and a huge "boot" on the end of the pubis, more than half as long as the shaft of the pubis itself. These features are found in all known tyrannosauroids, including basal members ''Guanlong'' and ''Dilong''. The pubis is not known in ''
Aviatyrannis ''Aviatyrannis'' is a genus of carnivorous tyrannosauroid theropod dinosaur from the Oxfordian-Tithonian stages of the Late Jurassic found in Portugal. Discovery and naming In 2000 Oliver Walter Mischa Rauhut reported the find of tyrannosauro ...
'' or ''
Stokesosaurus ''Stokesosaurus'' (meaning "Stokes' lizard") is a genus of small (around in length), carnivorous early tyrannosauroid theropod dinosaurs from the late Jurassic period of Utah, United States. History From 1960 onwards Utah geologist William L ...
'' but both show typical tyrannosauroid characters in the ilium. The hindlimbs of all tyrannosauroids, like most theropods, had four toes, although the first toe (the
hallux Toes are the digits (fingers) of the foot of a tetrapod. Animal species such as cats that walk on their toes are described as being '' digitigrade''. Humans, and other animals that walk on the soles of their feet, are described as being '' pl ...
) did not contact the ground. Tyrannosauroid hindlimbs are longer relative to body size than almost any other theropods, and show proportions characteristic of fast-running animals, including elongated
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 ...
e and
metatarsal The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the med ...
s. These proportions persist even in the largest adult ''Tyrannosaurus'', despite its probable inability to run. The third metatarsal of tyrannosaurids was pinched at the top between the second and fourth, forming a structure known as the
arctometatarsus An arctometatarsalian organism is one in which the proximal part of the middle metatarsal is pinched between the surrounding metatarsals. The trait appears to be highly homoplastic, common in certain sorts of dinosaurs accustomed to running (among ...
. The arctometatarsus was also present in ''Appalachiosaurus'' but it is unclear whether it was found in ''Eotyrannus'' or ''
Dryptosaurus ''Dryptosaurus'' ( ) is a genus of tyrannosauroid that lived approximately 67 million years ago (mya) during the latter part of the Cretaceous period, New Jersey. ''Dryptosaurus'' was a large, bipedal, ground-dwelling carnivore, that grow up to ...
''. This structure was shared by derived
ornithomimid 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 Laura ...
s,
troodontid 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 ...
s and
caenagnathid Caenagnathidae is a family of bird-like maniraptoran theropod dinosaurs from the Cretaceous of North America and Asia. They are a member of the Oviraptorosauria, and close relatives of the Oviraptoridae. Like other oviraptorosaurs, caenagnathids ...
s, but was not present in basal tyrannosauroids like ''
Dilong paradoxus ''Dilong'' (帝龍, which means 'emperor dragon') is a genus of basal tyrannosauroid dinosaur. The only species is ''Dilong paradoxus''. It is from the Lower Cretaceous Yixian Formation near Lujiatun, Beipiao, in the western Liaoning province of ...
'', indicating
convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
.


Classification

''Tyrannosaurus'' was named by
Henry Fairfield Osborn Henry Fairfield Osborn, Sr. (August 8, 1857 – November 6, 1935) was an American paleontologist, geologist and eugenics advocate. He was the president of the American Museum of Natural History for 25 years and a cofounder of the American Euge ...
in 1905, along with the family Tyrannosauridae. The name is derived from the
Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...
words ' ' ('tyrant') and ' ('lizard'). The superfamily name Tyrannosauroidea was first published in a 1964 paper by the
British British may refer to: Peoples, culture, and language * British people, nationals or natives of the United Kingdom, British Overseas Territories, and Crown Dependencies. ** Britishness, the British identity and common culture * British English, ...
paleontologist 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 ...
Alick Walker Alick Donald Walker (26 October 1925 – 4 December 1999) was a British palaeontologist, after whom the ''Alwalkeria'' genus of dinosaur is named. He was born in Skirpenbeck, near York and attended Pocklington School from 1936 to 1943. He began a ...
. The
suffix In linguistics, a suffix is an affix which is placed after the stem of a word. Common examples are case endings, which indicate the grammatical case of nouns, adjectives, and verb endings, which form the conjugation of verbs. Suffixes can carry ...
''-oidea'', commonly used in the name of animal superfamilies, is derived from the Greek ''ειδος'' ' ('form'). Scientists have commonly understood Tyrannosauroidea to include the tyrannosaurids and their immediate ancestors. With the advent of
phylogenetic taxonomy 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 ...
in vertebrate paleontology, however, 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, ...
has received several more explicit definitions. The first was by
Paul Sereno Paul Callistus Sereno (born October 11, 1957) is a professor of paleontology at the University of Chicago and a National Geographic "explorer-in-residence" who has discovered several new dinosaur species on several continents, including at sites ...
in 1998, where Tyrannosauroidea was defined as a stem-based
taxon 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 ...
including all species sharing a more recent common ancestor with ''Tyrannosaurus rex'' than with neornithean birds. To make the family more exclusive,
Thomas Holtz Thomas Richard Holtz Jr. (born September 13, 1965) is an American vertebrate palaeontologist, author, and principal lecturer at the University of Maryland's Department of Geology. He has published extensively on the phylogeny, morphology, ecomorp ...
redefined it in 2004 to include all species more closely related to ''Tyrannosaurus rex'' than to ''
Ornithomimus velox ''Ornithomimus'' (; "bird mimic") is a genus of ornithomimid dinosaurs from the Late Cretaceous Period of what is now North America. ''Ornithomimus'' was a swift bipedal theropod which fossil evidence indicates was covered in feathers, equipped ...
'', ''
Deinonychus antirrhopus ''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 ...
'' or ''
Allosaurus fragilis ''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 ...
''. Sereno published a new definition in 2005, using ''Ornithomimus edmontonicus'', ''
Velociraptor mongoliensis ''Velociraptor'' (; ) is a genus of small dromaeosaurid dinosaur that lived in Asia during the Late Cretaceous epoch, about 75 million to 71 million years ago. Two species are currently recognized, although others have been assigned in the pa ...
'' and ''
Troodon formosus ''Troodon'' ( ; ''Troödon'' in older sources) is a wastebasket taxon and a dubious genus of relatively small, bird-like dinosaurs known definitively from the Campanian age of the Late Cretaceous period (about 77  mya). It includes at least ...
'' as external specifiers. The Sereno definition was adopted in a 2010 review. Some studies have suggested that the clade
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 ...
, usually considered to be allosauroids, are basal tyrannosauroids. However, other authors disputed the placement of megaraptorans within Tyrannosauroidea, and a study of megaraptoran hand anatomy published in 2016 caused even the original scientists suggesting their tyrannosauroid relationships to at least partly reject their prior conclusion.


Phylogeny

While paleontologists have long recognized the family Tyrannosauridae, its ancestry has been the subject of much debate. For most of the twentieth century, tyrannosaurids were commonly accepted as members of the
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 ...
, which included almost all large theropods. Within this group, the
allosaurid 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 ...
s were often considered to be ancestral to tyrannosaurids. In the early 1990s, cladistic analyses instead began to place tyrannosaurids into the Coelurosauria, echoing suggestions first published in the 1920s. Tyrannosaurids are now universally considered to be large coelurosaurs. In 1994, Holtz grouped tyrannosauroids with elmisaurids, ornithomimosaurs and
troodont 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 disco ...
s into a coelurosaurian clade called Arctometatarsalia based on a common ankle structure where the second and fourth metatarsals meet near the tarsal bones, covering the third metatarsal when viewed from the front. Basal tyrannosauroids like ''Dilong'', however, were found with non-
arctometatarsalian An arctometatarsalian organism is one in which the proximal part of the middle metatarsal is pinched between the surrounding metatarsals. The trait appears to be highly homoplastic, common in certain sorts of dinosaurs accustomed to running (among ...
ankles, indicating that this feature evolved convergently. Arctometatarsalia has been dismantled and is no longer used by most paleontologists, with tyrannosauroids usually considered to be basal coelurosaurs outside
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 ...
. While many place tyrannosauroids as basal coelurosaurs, Paul Sereno in his 1990s analysis of theropods would find the Tyrannosaurs to be sister taxa to the Maniraptora with them being closer to birds than Ornithomimosaurs were. He called this group
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 ...
(which in the absence of papers that recover a Tyrannosaur-maniraptoran clade), is a clade which contains most Coelurosaurs. A 2007 analysis found the family
Coeluridae Coeluridae is a historically unnatural group of generally small, carnivorous dinosaurs from the late Jurassic Period. For many years, any small Jurassic or Cretaceous theropod that did not belong to one of the more specialized families recognize ...
, including the Late Jurassic North American genera ''
Coelurus ''Coelurus'' ( ) is a genus of coelurosaurian dinosaur from the Late Jurassic period (mid-late Kimmeridgian faunal stage, 155–152 million years ago). The name means "hollow tail", referring to its hollow tail vertebrae (Greek κοῖλο ...
'' and ''
Tanycolagreus ''Tanycolagreus'' is a genus of coelurosaurian theropod from the Late Jurassic of North America. Discovery and naming In 1995 Western Paleontological Laboratories, Inc. uncovered the partial skeleton of a small theropod at the Bone Cabin Quarr ...
'', to be the
sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...
of Tyrannosauroidea. The most basal tyrannosauroid known from complete skeletal remains is ''Guanlong,'' a representative of the family
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 ...
. Other early taxa include ''Stokesosaurus'' and ''Aviatyrannis'', known from far less complete material. The better-known ''Dilong'' is considered slightly more derived than ''Guanlong'' and ''Stokesosaurus''. ''
Dryptosaurus ''Dryptosaurus'' ( ) is a genus of tyrannosauroid that lived approximately 67 million years ago (mya) during the latter part of the Cretaceous period, New Jersey. ''Dryptosaurus'' was a large, bipedal, ground-dwelling carnivore, that grow up to ...
'', long a difficult genus to classify, has turned up in several recent analyses as a basal tyrannosauroid as well, slightly more distantly related to Tyrannosauridae than ''Eotyrannus'' and ''Appalachiosaurus''. ''
Alectrosaurus ''Alectrosaurus'' (; meaning "alone lizard") is a genus of tyrannosauroid theropod dinosaur that lived in Asia during the Late Cretaceous period, about some 96 million years ago in what is now the Iren Dabasu Formation. It was a medium-sized, mo ...
'', a poorly known genus from Mongolia, is definitely a tyrannosauroid but its exact relationships are unclear. Other taxa have been considered possible tyrannosauroids by various authors, including ''
Bagaraatan ''Bagaraatan'' (/'ba-ɣa-raa-tan/ meaning 'small' ''baɣa'' + 'carnivorous animal, beast of prey' ''araatan'' in Mongolian) is a genus of theropod dinosaur from the Late Cretaceous period. Its fossils were found in the Nemegt Formation of Mongoli ...
'' and ''
Labocania ''Labocania'' is a genus of carnivorous theropod dinosaur of uncertain affinities from Baja California, Mexico, which lived 73 million years ago, in the Campanian stage of the late Cretaceous Period. In the summer of 1970, the National Geog ...
''. ''
Siamotyrannus ''Siamotyrannus'' (meaning "Siamese tyrant") is a genus of theropod dinosaur from the early Cretaceous of Thailand. Discovery and naming In 1993, Somchai Traimwichanon found a partial skeleton of a large theropod at the Phu Wiang 9 site in Khon K ...
'' from 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 ...
of
Thailand Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is bo ...
was originally described as an early tyrannosaurid, but is usually considered a
carnosaur 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 ...
today. ''
Iliosuchus ''Iliosuchus'' (meaning "crocodile hipped") is a genus of theropod dinosaur known from Bathonian–age (168.3 – 166.1 mya) rocks of England. It was perhaps long.Holtz, Thomas R. Jr. (2008) ''Dinosaurs: The Most Complete, Up-to-Date Encycloped ...
'' has a vertical ridge on the ilium reminiscent of tyrannosauroids and may in fact be the earliest known member of the superfamily, but not enough material is known to be sure. Below is a cladogram by Loewen ''et al.'' in 2013 that included most tyrannosauroid species known at the time of its publication.


Phylogeography

In 2018 authors Rafael Delcourt and Orlando Nelson Grillo published a phylogenetic analysis of Tyrannosauroidea which incorporated taxa from the ancient continent of
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 ...
(which today consists of the southern hemisphere), such as ''
Santanaraptor ''Santanaraptor'' (meaning "Santana Formation thief") is a genus of Tyrannosauroidea, tyrannosauroid Theropoda, theropod dinosaur that lived in South America during the Early Cretaceous (late Aptian-early Albian), about 112 million years ago. Di ...
'' and ''
Timimus ''Timimus'' is a genus of small coelurosaurian theropod dinosaur from the Early Cretaceous of Australia. It was originally identified as an ornithomimosaur, but now it is thought to be a different kind of theropod, possibly a tyrannosauroid. Di ...
'', whose placement in the group has been controversial. They have found that not only ''Santanaraptor'' and ''Timimus'' were placed as tyrannosaurs more derived than ''Dilong'', but they have found in their analysis that tyrannosauroids were widespread in
Laurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pan ...
and Gondwana since the Middle Jurassic. They have proposed new subclade names for Tyrannosaurioidea. The first is Pantyrannosauria referring to all non-proceratosaurid members of the group, while
Eutyrannosauria Eutyrannosauria is a clade of tyrannosauroid theropods whose distribution has been found in what is now Asia and North America. The clade consists of an evolutionary grade of tyrannosaurs such as ''Appalachiosaurus'', ''Dryptosaurus'', and ''Bist ...
for larger tyrannosaur taxa found in the northern hemisphere such as ''Dryptosaurus'', ''Appalachiosaurus'', ''
Bistahieversor ''Bistahieversor'' (meaning "Bistahi destroyer"), also known as the "Bisti Beast", is a genus of eutyrannosaurian tyrannosauroid dinosaur; the genus contains only a single known species, ''B. sealeyi'', described in 2010, from the Late Cretaceo ...
'', and Tyrannosauridae. Below is their phylogeographic tree they have recovered, in which displays the phylogenetic relationships of the taxa as well as the continents those taxa have been found. In 2021, Chase Brownstein published a research article based on more thorough descriptions of tyrannosauroid
metatarsals The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medi ...
and vertebra from the
Merchantville Formation The Merchantville Formation is a geological formation in the northeastern United States whose strata date back to the Late Cretaceous, around the time of the Santonian and Campanian age. Dinosaur remains are among the fossils that have been recove ...
in
Delaware Delaware ( ) is a state in the Mid-Atlantic region of the United States, bordering Maryland to its south and west; Pennsylvania to its north; and New Jersey and the Atlantic Ocean to its east. The state takes its name from the adjacent Del ...
. This reanalysis of phylogenetic relationships of tyrannosauroids in Appalachia has brought the rediscovery of the clade
Dryptosauridae Eutyrannosauria is a clade of tyrannosauroid theropods whose distribution has been found in what is now Asia and North America. The clade consists of an evolutionary grade of tyrannosaurs such as '' Appalachiosaurus'', ''Dryptosaurus'', and '' B ...
due to the similarities of the metatarsals II and IV compared to the same bones in Dryptosaurus holotype. However the Merchantville taxon was able to still be different enough to separate it on the genus level from Dryptosaurus. In the phylogentic tree constructed Dryptosauridae is found to be a valid family of non tyrannosaurid eutyrannosaur. It currently sits in a potylomy with the Iren Dabasu taxon and more basal eutryannosaurs.


Distribution

The tyrannosauroids lived on the supercontinent
Laurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pan ...
, which split from
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 ...
in the
Middle Jurassic The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations co ...
. The earliest recognized tyrannosauroids lived in the Middle Jurassic, represented by the proceratosaurids ''
Kileskus ''Kileskus'' (meaning ''lizard'' in the Khakas language) is a genus of tyrannosauroid dinosaur known from partial remains found in Middle Jurassic (Bathonian stage) Itat Formation of Sharypovsky District, Krasnoyarsk Krai (Russia). Fossils rec ...
'' from the Western Siberia and ''
Proceratosaurus ''Proceratosaurus'' is a genus of carnivore, carnivorous theropod dinosaur from the Middle Jurassic (Bathonian) of England. ''Proceratosaurus'' was a small dinosaur, measuring in length and in body mass.Holtz, Thomas R. Jr. (2008) ''Dinosaurs: ...
'' from Great Britain. Upper Jurassic tyrannosauroids include ''
Guanlong ''Guanlong'' (冠龍) is a genus of extinct proceratosaurid tyrannosauroid from the Late Jurassic of China. The taxon was first described in 2006 by Xu Xing ''et al.'', who found it to represent a new taxon related to ''Tyrannosaurus''. The na ...
'' from China'','' ''
Stokesosaurus ''Stokesosaurus'' (meaning "Stokes' lizard") is a genus of small (around in length), carnivorous early tyrannosauroid theropod dinosaurs from the late Jurassic period of Utah, United States. History From 1960 onwards Utah geologist William L ...
'' from the western United States and ''
Aviatyrannis ''Aviatyrannis'' is a genus of carnivorous tyrannosauroid theropod dinosaur from the Oxfordian-Tithonian stages of the Late Jurassic found in Portugal. Discovery and naming In 2000 Oliver Walter Mischa Rauhut reported the find of tyrannosauro ...
'' and ''
Juratyrant ''Juratyrant'' (meaning "Jurassic tyrant") is a tyrannosauroid dinosaur genus from the late Jurassic period (early Tithonian age) of England. The genus contains a single species, ''Juratyrant langhami'', which was once classed as a species of ''S ...
'' from Europe. Early Cretaceous tyrannosauroids are known from Laurasia, being represented by ''
Eotyrannus ''Eotyrannus'' (meaning "dawn tyrant") is a genus of tyrannosauroid theropod dinosaur hailing from the Early Cretaceous Wessex Formation beds, included in Wealden Group, located in the southwest coast of the Isle of Wight, United Kingdom. The rem ...
'' from England and ''
Dilong ''Dilong'' (; lit. "earth dragon") is a Chinese dragon name that is also used to mean "earthworm" in traditional Chinese medicine and ''Geosaurus'' in zoological nomenclature. Dragon In Chinese mythology, ''dilong'' "earth dragon" is one of m ...
'', ''
Sinotyrannus ''Sinotyrannus'' (meaning "Chinese tyrant") is a genus of large basal tyrannosauroid dinosaur, known from a single incomplete fossil specimen including a partial skull, from the Early Cretaceous Jiufotang Formation of Liaoning, China. Specifical ...
'', and ''
Yutyrannus ''Yutyrannus'' (meaning "feathered tyrant") is a genus of proceratosaurid tyrannosauroid dinosaur which contains a single known species, ''Yutyrannus huali''. This species lived during the early Cretaceous period in what is now northeastern Chi ...
'' from northeastern China. Early Cretaceous tyrannosauroid premaxillary teeth are known from the
Cedar Mountain Formation The Cedar Mountain Formation is the name given to a distinctive sedimentary geologic formation in eastern Utah, spanning most of the early and mid-Cretaceous. The formation was named for Cedar Mountain (Utah), Cedar Mountain in northern Emery Coun ...
in
Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...
and the
Tetori Group The Tetori Group is a stratigraphic group in Japan, found within several basins in and around Fukui Prefecture. It is Early Cretaceous in age. It primarily consists of freshwater continental deposits, with some beds of volcanic tuffite. It primari ...
of
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
. The Middle Cretaceous record of Tyrannosauroidea is rather patchy. Teeth and indeterminate postcrania of this interval are known from the Cenomanian-age
Dakota Formation The Dakota is a sedimentary geologic unit name of formation and group rank in Midwestern North America. The Dakota units are generally composed of sandstones, mudstones, clays, and shales deposited in the Mid-Cretaceous opening of the Western Int ...
of western North America and
Potomac Formation The Potomac Group is a geologic group in Delaware, Maryland, New Jersey, and Virginia. It preserves fossils dating back to the Cretaceous period. An indeterminate tyrannosauroid and '' Priconodon crassus'', a nodosaurid, are known from indetermi ...
of New Jersey, as well as formations in
Kazakhstan Kazakhstan, officially the Republic of Kazakhstan, is a transcontinental country located mainly in Central Asia and partly in Eastern Europe. It borders Russia to the north and west, China to the east, Kyrgyzstan to the southeast, Uzbeki ...
and
Tajikistan Tajikistan (, ; tg, Тоҷикистон, Tojikiston; russian: Таджикистан, Tadzhikistan), officially the Republic of Tajikistan ( tg, Ҷумҳурии Тоҷикистон, Jumhurii Tojikiston), is a landlocked country in Centr ...
; two genera, ''Timurlengia'' and ''Xiongguanlong'', have been found in Asia, while the Brazilian ''Santanaraptor'' may belong to this group. ''
Suskityrannus ''Suskityrannus'' (meaning "coyote tyrant", ''suski'' meaning "coyote" in Zuni) is a genus of small tyrannosauroid theropod from the Late Cretaceous in southern Laramidia. It contains a single species, ''Suskityrannus hazelae,'' believed to h ...
'' has been found in the
Moreno Hill Formation The Moreno Hill Formation is a geological formation in western New Mexico whose strata were deposited in the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.Weishampel, David B; et al. (2004). " ...
of the Zuni Basin of western New Mexico. The first unquestionable remains of tyrannosaurids occur in the
Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campanian s ...
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 ...
of the Late Cretaceous in North America and Asia. Two subfamilies are recognized. The albertosaurines are only known from North America, while the tyrannosaurines are found on both continents. Tyrannosaurid fossils have been found in
Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S., ...
, which may have served as a land bridge allowing dispersal between the two continents. Non-tyrannosaurid tyrannosauroids like ''Alectrosaurus'' and possibly ''Bagaraatan'' were contemporaneous with tyrannosaurids in Asia, while they are absent from western North America. Eastern North America was divided by the
Western Interior Seaway The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, and the Western Interior Sea) was a large inland sea that split the continent of North America into two landmasses. The ancient sea, ...
in the middle of the Cretaceous and isolated from the western portion of the continent. The absence of tyrannosaurids from the eastern part of the continent suggests that the family evolved after the appearance of the seaway, allowing basal tyrannosauroids like ''Dryptosaurus'' and ''Appalachiosaurus'' to survive in the east as a
relict population In biogeography and paleontology, a relict is a population or taxon of organisms that was more widespread or more diverse in the past. A relictual population is a population currently inhabiting a restricted area whose range was far wider during a ...
until the end of the Cretaceous. Basal tyrannosauroids have also been suggested to be present in
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 ...
and South America during the Early Cretaceous. NMV P186069, a partial pubis (a hip bone) with a supposed distinctive tyrannosauroid-like form, was discovered in
Dinosaur Cove The Dinosaur Cove in Victoria, Australia is a fossil-bearing site in the south-east of the continent where the Otway Ranges meet the sea to the west of Cape Otway, adjacent to Great Otway National Park (''map''). The inaccessible ocean-front clif ...
in
Victoria Victoria most commonly refers to: * Victoria (Australia), a state of the Commonwealth of Australia * Victoria, British Columbia, provincial capital of British Columbia, Canada * Victoria (mythology), Roman goddess of Victory * Victoria, Seychelle ...
. However, a response suggested that critical tyrannosauroid characters were absent from the fossil. The Australian taxon ''
Timimus ''Timimus'' is a genus of small coelurosaurian theropod dinosaur from the Early Cretaceous of Australia. It was originally identified as an ornithomimosaur, but now it is thought to be a different kind of theropod, possibly a tyrannosauroid. Di ...
'', known from a femur, and the Brasilian ''
Santanaraptor ''Santanaraptor'' (meaning "Santana Formation thief") is a genus of Tyrannosauroidea, tyrannosauroid Theropoda, theropod dinosaur that lived in South America during the Early Cretaceous (late Aptian-early Albian), about 112 million years ago. Di ...
'', known from a partial juvenile skeleton, have also been suggested to be tyrannosaurs. However, these placements have been considered questionable, with the supposed tyrannosauroid characters of ''Santanaraptor'' being widely distributed within Coelurosauria, in other characters having similarities to noasaurids.


Paleobiology


Facial tissue

A conference paper by Tracy Ford states that there was rough bone texture on the skulls of theropods and higher foramina frequency than
lepidosaurs The Lepidosauria (, from Greek meaning ''scaled lizards'') is a subclass or superorder of reptiles, containing the orders Squamata and Rhynchocephalia. Squamata includes snakes, lizards, and amphisbaenians. Squamata contains over 9,000 species ...
and
mammals 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 ...
which would be evidential for a sensitive snout for theropods. A study in 2017 study about a new tyrannosaurid named ''
Daspletosaurus horneri ''Daspletosaurus'' ( ; meaning "frightful lizard") is a genus of tyrannosaurid dinosaur that lived in Laramidia between about 79.5 and 74 million years ago, during the Late Cretaceous Period. The genus ''Daspletosaurus'' contains three species ...
'' was published in the journal Scientific Reports. Paleontologist Thomas Carr analyzed the craniofacial
texture Texture may refer to: Science and technology * Surface texture, the texture means smoothness, roughness, or bumpiness of the surface of an object * Texture (roads), road surface characteristics with waves shorter than road roughness * Texture (c ...
of ''Daspletosaurus horneri'' and observed a hummocky rugosity which compared to crocodilian skulls and suggesting ''Daspletosaurus horneri'' including all tyrannosaurids have flat sensory scales. The subordinate regions were analyzed to have cornified epidermis. However, a 2018 presentation has an alternative interpretation. Crocodilians don't have flat sensory scales but rather cracked cornified epidermis due to growth. The hummocky rugosity in the skulls of lepidosaurs have correlation with scales which this bone texture is also present in tyrannosaurid skulls. The foramina frequency in theropod skulls does not exceed 50 foramina which shows that theropods had lips. It's been proposed that lips are a primitive trait in tetrapods and the soft tissue present in crocodilians are a derived trait because of aquatic or semiaquatic adaptations.


Body integument

Long
filamentous The word filament, which is descended from Latin ''filum'' meaning " thread", is used in English for a variety of thread-like structures, including: Astronomy * Galaxy filament, the largest known cosmic structures in the universe * Solar filament ...
structures have been preserved along with skeletal remains of numerous coelurosaurs from the Early Cretaceous
Yixian Formation The Yixian Formation (; formerly transcribed as Yihsien Formation) is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the late Barremian and early Aptian stages of the Early Cretaceous. It is known for its ex ...
and other nearby
geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...
s from
Liaoning Liaoning () is a coastal province in Northeast China that is the smallest, southernmost, and most populous province in the region. With its capital at Shenyang, it is located on the northern shore of the Yellow Sea, and is the northernmost ...
, China. These filaments have usually been interpreted as "protofeathers," homologous with the branched feathers found in birds and some non-avian theropods, although other hypotheses have been proposed. A skeleton of ''Dilong'' was described in 2004 that included the first example of feathers in a tyrannosauroid. Similarly to
down feather The down of birds is a layer of fine feathers found under the tougher exterior feathers. Very young birds are clad only in down. Powder down is a specialized type of down found only in a few groups of birds. Down is a fine thermal insulator an ...
s of modern birds, the feathers found in ''Dilong'' were branched but not
pennaceous The pennaceous feather is a type of feather present in most modern birds and in some other species of maniraptoriform dinosaurs. Description A pennaceous feather has a stalk or quill. Its basal part, called a ''calamus'', is embedded in the skin ...
, and may have been used for
insulation Insulation may refer to: Thermal * Thermal insulation, use of materials to reduce rates of heat transfer ** List of insulation materials ** Building insulation, thermal insulation added to buildings for comfort and energy efficiency *** Insulated ...
. Even large tyrannosauroids have been found with evidence of feathers. ''
Yutyrannus huali ''Yutyrannus'' (meaning "feathered tyrant") is a genus of proceratosaurid tyrannosauroid dinosaur which contains a single known species, ''Yutyrannus huali''. This species lived during the early Cretaceous period in what is now northeastern Chi ...
'', also from the Yixian Formation, is known from three specimens, each preserving traces of feathers on various parts of the body. While not all areas of the body preserve impressions across all three specimens, these fossils demonstrate that even in this medium-sized species, most of the body was covered in feathers. The presence of feathers in basal tyrannosauroids is not surprising since they are now known to be characteristic of coelurosaurs, found in other basal genera like ''
Sinosauropteryx ''Sinosauropteryx'' (meaning "Chinese reptilian wing", ) is a compsognathid dinosaur. Described in 1996, it was the first dinosaur taxon outside of Avialae (birds and their immediate relatives) to be found with evidence of feathers. It was covere ...
'', as well as all more derived groups. Rare fossilized
skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...
impressions of some Late Cretaceous tyrannosaurids lack feathers, however, instead showing skin covered in fine, non-overlapping
scales Scale or scales may refer to: Mathematics * Scale (descriptive set theory), an object defined on a set of points * Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original * Scale factor, a number w ...
. Possibly, feathers were present on other areas of the body: Preserved skin impressions are very small and come primarily from the legs, pelvic region, and underside of the tail, which either lack feathers or only covered in a light down in some modern larger ground-dwelling birds. Alternatively, secondary loss of feathers in large tyrannosaurids may be
analogous Analogy (from Greek ''analogia'', "proportion", from ''ana-'' "upon, according to" lso "against", "anew"+ ''logos'' "ratio" lso "word, speech, reckoning" is a cognitive process of transferring information or meaning from a particular subject ( ...
with the similar loss of
hair Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals. The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and f ...
in the largest modern mammals like
elephant Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantidae an ...
s, where a low
surface area The surface area of a solid object is a measure of the total area that the surface of the object occupies. The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the definition of arc ...
-to-
volume Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). The de ...
ratio slows down
heat transfer Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, ...
, making insulation by a coat of hair unnecessary or even detrimental. A scientific publication by Phil Bell and colleagues in 2017 show that tyrannosaurids such as ''Gorgosaurus'', ''Tarbosaurus'', ''Albertosaurus'', ''Daspletosaurus'', and ''Tyrannosaurus'' had scales. The Bell et al. 2017 paper notes that the scale-like integument on bird feet were actually secondarily derived feathers according to paleontological and evolutionary developmental evidence so they hypothesize that the scaly skin preserved on some tyrannosaurid specimens might be secondarily derived from filamentous appendages like on Yutyrannus although strong evidence is needed to support this hypothesis. However, other paleontologists argue that taphonomy is the possible cause of the lack of filamentous structures in tyrannosaurid fossils.


Head crests

Bony crests are found on the skulls of many theropods, including numerous tyrannosauroids. The most elaborate is found in ''Guanlong'', where the nasal bones support a single, large crest which runs along the midline of the skull from front to back. This crest was penetrated by several large foramina (openings) which reduced its weight. A less prominent crest is found in ''Dilong'', where low, parallel ridges run along each side of the skull, supported by the nasal and
lacrimal bone The lacrimal bone is a small and fragile bone of the facial skeleton; it is roughly the size of the little fingernail. It is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders. Several bony landmarks of ...
s. These ridges curve inwards and meet just behind the nostrils, making the crest ''Y''-shaped. The fused nasals of tyrannosaurids are often very rough-textured. ''
Alioramus ''Alioramus'' (; meaning 'different branch') is a genus of tyrannosaurid theropod dinosaurs from the Late Cretaceous period of Asia. It currently contains two species. The type species, ''A. remotus'' is known from a partial skull and three foo ...
'', a possible tyrannosaurid from Mongolia, bears a single row of five prominent bony bumps on the nasal bones; a similar row of much lower bumps is present on the skull of ''Appalachiosaurus'', as well as some specimens of ''
Daspletosaurus ''Daspletosaurus'' ( ; meaning "frightful lizard") is a genus of tyrannosaurid dinosaur that lived in Laramidia between about 79.5 and 74 million years ago, during the Late Cretaceous Period. The genus ''Daspletosaurus'' contains three species ...
'', ''Albertosaurus'', and ''Tarbosaurus''. In ''Albertosaurus'', ''Gorgosaurus'' and ''
Daspletosaurus ''Daspletosaurus'' ( ; meaning "frightful lizard") is a genus of tyrannosaurid dinosaur that lived in Laramidia between about 79.5 and 74 million years ago, during the Late Cretaceous Period. The genus ''Daspletosaurus'' contains three species ...
'', there is a prominent horn in front of each eye on the lacrimal bone. The lacrimal horn is absent in ''Tarbosaurus'' and ''Tyrannosaurus'', which instead have a crescent-shaped crest behind each eye on the
postorbital bone The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some ve ...
. These head crests may have been used for
display Display may refer to: Technology * Display device, output device for presenting information, including: ** Cathode ray tube, video display that provides a quality picture, but can be very heavy and deep ** Electronic visual display, output devi ...
, perhaps for species recognition or
courtship Courtship is the period wherein some couples get to know each other prior to a possible marriage. Courtship traditionally may begin after a betrothal and may conclude with the celebration of marriage. A courtship may be an informal and private m ...
behavior. An example of the
handicap principle The handicap principle is a hypothesis proposed by the biologist Amotz Zahavi to explain how evolution may lead to "honest" or reliable signalling between animals which have an obvious motivation to bluff or deceive each other. It suggests that ...
may be the case of ''Guanlong'', where the large, delicate crest may have been a hindrance to hunting in what was presumably an active predator. If an individual was healthy and successful at hunting despite the fragile crest, it would indicate the superior quality of the individual over others with smaller crests. Similarly to the unwieldy tail of a male
peacock Peafowl is a common name for three bird species in the genera ''Pavo (genus), Pavo'' and ''Afropavo'' within the tribe Pavonini of the family Phasianidae, the pheasants and their allies. Male peafowl are referred to as peacocks, and female pea ...
or the outsized
antlers Antlers are extensions of an animal's skull found in members of the Cervidae (deer) family. Antlers are a single structure composed of bone, cartilage, fibrous tissue, skin, nerves, and blood vessels. They are generally found only on male ...
of an
Irish elk The Irish elk (''Megaloceros giganteus''), also called the giant deer or Irish deer, is an extinct species of deer in the genus ''Megaloceros'' and is one of the largest deer that ever lived. Its range extended across Eurasia during the Pleisto ...
, the crest of ''Guanlong'' may have evolved via
sexual selection Sexual selection is a mode of natural selection in which members of one biological sex mate choice, choose mates of the other sex to mating, mate with (intersexual selection), and compete with members of the same sex for access to members of t ...
, providing an advantage in courtship that outweighed any decrease in hunting ability.


Reproduction

Neonate An infant or baby is the very young offspring of human beings. ''Infant'' (from the Latin word ''infans'', meaning 'unable to speak' or 'speechless') is a formal or specialised synonym for the common term ''baby''. The terms may also be used to ...
sized tyrannosaur fossils have been documented in the
scientific literature : ''For a broader class of literature, see Academic publishing.'' Scientific literature comprises scholarly publications that report original empirical and theoretical work in the natural and social sciences. Within an academic field, scient ...
.


References


External links


List of tyrannosauroid specimens and species
at The Theropod Database. {{Taxonbar, from=Q131396 Middle Jurassic first appearances Maastrichtian extinctions