''Tenontosaurus'' ( ; ) is a
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 ...
of medium- to large-sized
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 wo ...
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 ...
. It was a relatively medium sized ornithopod, reaching in length and in body mass. It had an unusually long, broad tail, which like its back was stiffened with a network of bony tendons.
The genus is known from the late
Aptian
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), a ...
to
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0.9 M ...
ages of 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 ...
period sediments of western
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 ...
, dating between 115 and 108 million years ago. It contains two species, ''Tenontosaurus tilletti'' (described 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 ...
in 1970) and ''Tenontosaurus dossi'' (described by Winkler, Murry, and Jacobs in 1997). Many specimens of ''T. tilletti'' have been collected from several geological formations throughout western North America. ''T. dossi'' is known from only a handful of
specimens collected from the
Twin Mountains Formation
The Twin Mountains Formation, also known as the Twin Mak Formation, is a sedimentary rock formation, within the Trinity Group, found in Texas of the United States of America. It is a terrestrial formation of Aptian age (Lower Cretaceous), and ...
of
Parker County,
Texas
Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...
.
History of discovery
![Iguanodontian Sizes](https://upload.wikimedia.org/wikipedia/commons/5/5a/Iguanodontian_Sizes.svg)
The first ''Tenontosaurus''
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 ...
was found in
Big Horn County,
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 ...
by an
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 ...
(AMNH) expedition in 1903. Subsequent digs in the same area during the 1930s unearthed 18 more specimens, and four specimens were found during the 1940s. Despite the large number of fossil specimens, the animal was not named or scientifically described during this time, though
Barnum Brown
Barnum Brown (February 12, 1873 – February 5, 1963), commonly referred to as Mr. Bones, was an American paleontologist. Named after the circus showman P. T. Barnum, he discovered the first documented remains of ''Tyrannosaurus'' during a career ...
of the AMNH gave it the informal name "Tenantosaurus", "sinew lizard", in reference to the extensive system of stiffening tendons in its back and tail.
[Forster, C.A. (1984). "The paleoecology of the ornithopod dinosaur ''Tenontosaurus tilletti'' from the Cloverly Formation, Big Horn Basin of Wyoming and Montana." ''The Mosasaur'', 2: 151–163.]
During the 1960s,
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 ...
began an extensive, long-term dig in the Big Horn Basin area (
Cloverly Formation
The Cloverly Formation is a geological formation of Early and Late Cretaceous age (Valanginian to Cenomanian stage) that is present in parts of Montana, Wyoming, Colorado and Utah in the western United States. It was named for a post office on th ...
) of Montana and
Wyoming
Wyoming () is a U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the south ...
. The expedition was led 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 ...
, whose team discovered more than 40 new specimens. Following his expedition, Ostrom became the first to describe and name the animal, calling it ''Tenontosaurus'', a slight variation in spelling of Brown's informal name.
Since 1970, many more ''Tenontosaurus'' specimens have been reported, both from the Cloverly and other geological formations, including the
Antlers Formation
The Antlers Formation is a stratum which ranges from Arkansas through southern Oklahoma into northeastern Texas. The stratum is thick consisting of silty to sandy mudstone and fine to coarse grained sandstone that is poorly to moderately sorted. ...
in
Oklahoma
Oklahoma (; Choctaw language, Choctaw: ; chr, ᎣᎧᎳᎰᎹ, ''Okalahoma'' ) is a U.S. state, state in the South Central United States, South Central region of the United States, bordered by Texas on the south and west, Kansas on the nor ...
,
Paluxy Formation of
Texas
Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...
,
Wayan Formation of
Idaho
Idaho ( ) is a state in the Pacific Northwest region of the Western United States. To the north, it shares a small portion of the Canada–United States border with the province of British Columbia. It borders the states of Montana and Wyom ...
,
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 ...
of
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
Arundel Formation
The Arundel Formation, also known as the Arundel Clay, is a clay-rich sedimentary rock formation, within the Potomac Group, found in Maryland of the United States of America. It is of Aptian age (Lower Cretaceous). This rock unit had been econ ...
of
Maryland
Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean to ...
.
[
]
Classification
The cladogram
A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...
below follows an analysis by Butler ''et al'', 2011.
Paleobiology
Diet
Plant life in the ''Tenontosaurus'' ecosystem was likely dominated by fern
A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except t ...
s and tree fern
The tree ferns are arborescent (tree-like) ferns that grow with a trunk elevating the fronds above ground level, making them trees. Many extant tree ferns are members of the order Cyatheales, to which belong the families Cyatheaceae (scaly tree ...
s, cycad
Cycads are seed plants that typically have a stout and woody (ligneous) trunk (botany), trunk with a crown (botany), crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants o ...
s, and possibly primitive flowering plants. Larger plants and trees were represented by 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 ...
s, such as 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 ...
and ginkgo
''Ginkgo'' is a genus of non-flowering seed plants. The scientific name is also used as the English name. The order to which it belongs, Ginkgoales, first appeared in the Permian, 270 million years ago, and is now the only living genus within ...
trees. ''Tenontosaurus'' was a low browser, and an adult would have had a maximum browsing height of about if it adopted a bipedal stance. This restricted ''Tenontosaurus'', especially juveniles, to eating low-growing ferns and shrubs. Its powerful, U-shaped beak and the angled cutting surfaces of its teeth, however, meant it was not limited to which part of the plant it consumed. Leaves, wood, and even fruit may have formed part of its diet.[
]
Predators
Teeth and a number of skeletons belonging to the carnivorous theropod ''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 ...
'' have often been discovered associated with ''Tenontosaurus tilletti'' remains. ''Tenontosaurus'' specimens have been found at over 50 sites, and 14 of those also contain ''Deinonychus'' remains. According to one 1995 study, only six sites containing ''Deinonychus'' fossils contain no trace of ''Tenontosaurus'', and ''Deinonychus'' remains are only rarely found associated with other potential prey, like ''Sauropelta
''Sauropelta'' ( ; meaning 'lizard shield') is a genus of nodosaurid dinosaur that existed in the Early Cretaceous Period of North America. One species (''S. edwardsorum'') has been named although others may have existed. Anatomically, ''Saurop ...
''.
abstract
) In all, 20% of ''Tenontosaurus'' fossils are found in close proximity to ''Deinonychus'', and several scientists have suggested that this implies ''Deinonychus'' was the major predator of ''Tenontosaurus''. Adult ''Deinonychus'', however, were much smaller than adult ''Tenontosaurus'', and it is unlikely a single ''Deinonychus'' would have been capable of attacking a fully grown ''Tenontosaurus''. While some scientists have suggested that ''Deinonychus'' must therefore have been a pack hunter, this view has been challenged based on both a supposed lack of evidence for coordinated hunting (rather than mobbing behavior as in most modern birds and reptiles, though crocodilians have been documented to hunt cooperatively on occasion) as well as evidence that ''Deinonychus'' may have been cannibalizing each other, as well as the ''Tenontosaurus'', in a feeding frenzy. It is likely that ''Deinonychus'' favored juvenile ''Tenontosaurus'', and that when ''Tenontosaurus'' reached a certain size, it passed out of range as a food source for the small theropods, though they may have scavenged larger individuals, or preyed on adults that were sick or injured. The fact that most ''Tenontosaurus'' remains found with ''Deinonychus'' are half-grown individuals supports this view. It also lived in the same area as the large carnivorous dinosaur ''Acrocanthosaurus
''Acrocanthosaurus'' ( ; ) is a genus of carcharodontosaurid dinosaur that existed in what is now North America during the Aptian and early Albian stages of the Early Cretaceous, from 113 to 110 million years ago. Like most dinosaur genera, ' ...
''.
Reproduction
The presence of medullary bone tissue in the thigh bone
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 wit ...
and shin bone
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 ...
of one specimen indicates that ''Tenontosaurus'' used this tissue, today only found in 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 that are laying eggs, in reproduction. Additionally, like ''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 ''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" alludin ...
'', two other dinosaurs known to have produced medullary bone, the tenontosaur individual was not at full adult size upon her death at 8 years old. Because the 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 ...
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 dinosaurs in general produced medullary tissue and reached reproductive maturity before maximum size. A histological
Histology,
also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures vis ...
study showed that ''T. tilletti'' grew quickly early in life and during sub-adult ontogeny
Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the stu ...
, but grew very slowly in the years approaching maturity, unlike other iguanodontians.
Paleoecology
Throughout the Cloverly Formation, ''Tenontosaurus'' is by far the most common vertebrate, five times more abundant than the next most common, the ankylosaur ''Sauropelta
''Sauropelta'' ( ; meaning 'lizard shield') is a genus of nodosaurid dinosaur that existed in the Early Cretaceous Period of North America. One species (''S. edwardsorum'') has been named although others may have existed. Anatomically, ''Saurop ...
''. In the arid Little Sheep Mudstone Member, ''Tenontosaurus'' is the only herbivorous dinosaur, and it shared its environment with the common predator ''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 ...
'' as well as an indeterminate species of allosauroid
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 ...
theropod and goniopholid crocodile. After the major climate shift at the beginning of the Himes Member in the mid-Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0.9 M ...
age, several more dinosaurs entered the region, including the less common ornithopod ''Zephyrosaurus
''Zephyrosaurus'' (meaning "westward wind lizard") is a genus of orodromine ornithischian dinosaur. It is based on a partial skull and postcranial fragments discovered in the Aptian-Albian-age Lower Cretaceous Cloverly Formation of Carbon Count ...
'', the oviraptorosaur
Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period (geology), Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like s ...
''Microvenator
''Microvenator'' (meaning "small hunter") is a genus of dinosaur from the Early Cretaceous Cloverly Formation in what is now south central Montana. ''Microvenator'' was an oviraptorosaurian theropod. The holotype fossil is an incomplete skeleton ...
'', and an indeterminate species of titanosauriform
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 ...
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 ...
and 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 ...
. The ecological community in the tropical stage also included the small 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 ...
''Gobiconodon
''Gobiconodon'' is an extinct genus of carnivorous mammal from the Middle Jurassic to Early Cretaceous. It weighed , had a skull of in length, and had in presacral body length. It was one of the largest mammals known from the Mesozoic. Like o ...
'', 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 such as ''Glyptops
''Glyptops'' (Greek for "grooved face") is an extinct genus of pleurosternid freshwater turtle known from the Late Jurassic of North America.
Taxonomy
The type species, ''Glyptops plicatulus'', was first described as ''Compsemys plicatulus'' by ...
'', and species of lungfish
Lungfish are freshwater vertebrates belonging to the order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, i ...
''.[
The ecological community was similar in other regions, with dinosaurs like ''Tenontosaurus'' and ''Deinonychus'' as the most common large vertebrates. The ]Antlers Formation
The Antlers Formation is a stratum which ranges from Arkansas through southern Oklahoma into northeastern Texas. The stratum is thick consisting of silty to sandy mudstone and fine to coarse grained sandstone that is poorly to moderately sorted. ...
stretches from southwest Arkansas through southeastern Oklahoma and into northeastern Texas. This geological formation has not been dated radiometrically. Scientists have used biostratigraphic data and the fact that it shares several of the same genera as the Trinity Group of Texas, to surmise that this formation was laid down during the Albian stage of the Early Cretaceous Period, approximately 110 mya. The area preserved in this formation was a large floodplain
A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...
that drained into a shallow inland sea. Several million years later, this sea would expand to the north, becoming 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 ...
and dividing North America in two for nearly the entire 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 ...
period. The paleoenvironment of the Antlers Formation consisted of tropical or sub-tropical forests, floodplains, river delta
A river delta is a landform shaped like a triangle, created by deposition (geology), deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, res ...
s, coastal swamps, bayous and lagoons, probably similar to that of modern-day Louisiana
Louisiana , group=pronunciation (French: ''La Louisiane'') is a state in the Deep South and South Central regions of the United States. It is the 20th-smallest by area and the 25th most populous of the 50 U.S. states. Louisiana is borde ...
. In the Antlers Formation
The Antlers Formation is a stratum which ranges from Arkansas through southern Oklahoma into northeastern Texas. The stratum is thick consisting of silty to sandy mudstone and fine to coarse grained sandstone that is poorly to moderately sorted. ...
in what is now Oklahoma, ''Tenontosaurus'' and ''Deinonychus'' shared their paleoenvironment
Paleoecology (also spelled palaeoecology) is the study of interactions between organisms and/or interactions between organisms and their environments across geologic timescales. As a discipline, paleoecology interacts with, depends on and informs ...
with other dinosaurs, such as the sauropods
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 b ...
''Astrodon
''Astrodon'' (aster: star, odon: tooth) is a genus of large herbivorous sauropod dinosaur, measuring in length, in height and in body mass. It lived in what is now the eastern United States during the Early Cretaceous period, and fossils have ...
'' (Pleurocoelus) and ''Sauroposeidon
''Sauroposeidon'' ( ; meaning "lizard earthquake god", after the Greek god Poseidon) is a genus of sauropod dinosaur known from several incomplete specimens including a bone bed and fossilized trackways that have been found in the U.S. states of ...
proteles'', and the 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 ...
''Acrocanthosaurus
''Acrocanthosaurus'' ( ; ) is a genus of carcharodontosaurid dinosaur that existed in what is now North America during the Aptian and early Albian stages of the Early Cretaceous, from 113 to 110 million years ago. Like most dinosaur genera, ' ...
atokensis'', which was likely the apex predator
An apex predator, also known as a top predator, is a predator at the top of a food chain, without natural predators of its own.
Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the highest trophic lev ...
in this region. The most common dinosaur in the paleoenvironment preserved in this formation is ''Tenontosaurus''. Other vertebrates present at the time of ''Tenontosaurus'' included the amphibian
Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...
'' Albanerpeton arthridion'', the reptiles ''Atokasaurus metarsiodon'' and ''Ptilotodon wilsoni'', the crurotarsan
Crurotarsi is a clade of archosauriform reptiles that includes crocodilians and stem-crocodilians and possibly bird-line archosaurs too if the extinct, crocodile-like phytosaurs are more distantly related to crocodiles than traditionally thoug ...
reptile ''Bernissartia
''Bernissartia'' ('of Bernissart') is an extinct genus of neosuchian crocodyliform that lived in the Early Cretaceous, around 130 million years ago.
At only in length, ''Bernissartia'' is one of the smallest crocodyliforms that ever lived. It ...
'', the cartilaginous
Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck and ...
fish ''Hybodus
''Hybodus'' (from el, ύβος , 'crooked' and el, ὀδούς 'tooth') is an extinct genus of hybodont, a group of shark-like elasmobranchs that lived from the Late Devonian to the end of the Cretaceous. Species closely related to the type sp ...
buderi'' and ''Lissodus
''Lissodus'' is an extinct genus of freshwater shark. It lived from the Early Carboniferous stage to the Albian age of the Cretaceous. It was about long and had flat teeth that it used for eating clams
Clam is a common name for several ...
anitae'', the ray-finned
Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species.
The ray-finned fishes are so called because their fins are webs of skin supported by bony or hor ...
fish ''Gyronchus
''Gyronchus'' is an extinct genus of prehistoric ray-finned fish from the Jurassic.
See also
* Prehistoric fish
The evolution of fish began about 530 million years ago during the Cambrian explosion. It was during this time that the early ...
dumblei'', the crocodilian ''Goniopholis
''Goniopholis'' (meaning "angled scale") is an extinct genus of goniopholidid crocodyliform that lived in Europe and Africa during the Late Jurassic and Early Cretaceous. Being semi-aquatic it is very similar to modern crocodiles. It ranged from ...
'', and the turtles ''Glyptops
''Glyptops'' (Greek for "grooved face") is an extinct genus of pleurosternid freshwater turtle known from the Late Jurassic of North America.
Taxonomy
The type species, ''Glyptops plicatulus'', was first described as ''Compsemys plicatulus'' by ...
'' and ''Naomichelys''. Possible indeterminate bird remains are also known from the Antlers Formation. The fossil evidence suggests that the gar
Gars are members of the family Lepisosteidae, which are the only surviving members of the Ginglymodi, an ancient holosteian group of ray-finned fish, which first appeared during the Triassic, over 240 million years ago. Gars comprise seven livin ...
''Lepisosteus
''Lepisosteus'' is a genus of gars in the family Lepisosteidae.
Distribution
While in the present day, ''Lepisosteus'' is only known across North America, fossil remains show it was much more widespread in the past, with specimens known from t ...
'' was the most common vertebrate in this region. The early mammals known from this region include ''Atokatherium boreni'' and ''Paracimexomys
''Paracimexomys'' is a genus of extinct mammals in the also extinct Multituberculata order. ''Paracimexomys'' lived during the Cretaceous period. The few fossils remains come from North America. Some Romanian fossils were also tentatively assig ...
crossi''.[Kielan-Jarorowska, Z., and Cifelli, R.L. 2001. Primitive boreosphenidan mammal (?Deltatheroida) from the Early Cretaceous of Oklahoma. Acta Palaeontologica Polonica 46: 377-391.]
Climate
In the Cloverly Formation
The Cloverly Formation is a geological formation of Early and Late Cretaceous age (Valanginian to Cenomanian stage) that is present in parts of Montana, Wyoming, Colorado and Utah in the western United States. It was named for a post office on th ...
of Montana and Wyoming, ''Tenontosaurus'' remains are common in two distinct rock units: the more ancient Little Sheep Mudstone Member (Cloverly Formation unit V) and the more recent Himes Member (units VI and VII). The oldest part of the formation, the Pryor Conglomerate, contains no ''Tenontosaurus'' fossils, and they only appear in the uppermost, most recent part of the Little Sheep Mudstone Member. Catherine Forster, in a 1984 paper on the ecology of ''Tenontosaurus'', used this as evidence to suggest that ''Tenontosaurus'' populations did not arrive in the Bighorn Basin area until the time of the late Little Sheep Mudstone Member.[
At the time ''Tenontosaurus'' first appeared in Wyoming and Montana (the early Albian age), the regions climate was ]arid
A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most ar ...
to semi-arid, dry, with seasonal periods of rainfall and occasional droughts. However, during a period of a few million years, the climate in the region shifted to one of increased rainfall, and the environment became subtropical
The subtropical zones or subtropics are geographical zone, geographical and Köppen climate classification, climate zones to the Northern Hemisphere, north and Southern Hemisphere, south of the tropics. Geographically part of the Geographical z ...
to tropical
The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in
the Southern Hemisphere at S. The tropics are also referred to ...
, with river deltas, floodplains, and forests with swampy inlets reminiscent of modern Louisiana
Louisiana , group=pronunciation (French: ''La Louisiane'') is a state in the Deep South and South Central regions of the United States. It is the 20th-smallest by area and the 25th most populous of the 50 U.S. states. Louisiana is borde ...
, though marked dry seasons persisted to create savannah-like environments as well. The change in rainfall levels is likely due to the advancing shoreline of the Skull Creek Seaway, a cycle of 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 ...
which, later in the Cretaceous period, would completely divide North America.[
This dramatic shift in climate coincided with an apparent increase, rather than decrease, in the abundance of ''Tenontosaurus''. This shows ''Tenontosaurus'' to have been a remarkably adaptable animal, which persisted for a long span of time in one area despite changes to its environment.][
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References
External links
{{Taxonbar, from=Q131103
Early Cretaceous dinosaurs of North America
Fossil taxa described in 1970
Iguanodonts
Taxa named by John Ostrom
Paleontology in Montana
Ornithischian genera