Tenontosaurus
Encyclopedia
Tenontosaurus is a genus
of medium- to large-sized ornithopod
dinosaur
. The genus is known from the late Aptian to Albian ages of the middle Cretaceous
period sediments of western North America
, dating between 115 to 108 million years ago. It was formerly thought to be a 'hypsilophodont', but since Hypsilophodontia is no longer considered a clade
, it is now considered to be a very primitive iguanodont
.
The genus contains two species, Tenontosaurus tilletti (described by John Ostrom
in 1970) and Tenontosaurus dossi (described by Winkler, Murray, 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
of Parker County, Texas
.
It was about 6.5 to 8 m (21.3 to 26.2 ft) long and 3 metres (9.8 ft) high in a bipedal stance, with a mass of somewhere between 1 to 2 t (1.1 to 2.2 ST). It had an unusually long, broad tail, which like its back was stiffened with a network of bony tendons.
by an American Museum of Natural History
(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
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.
During the 1960s, Yale University
began an extensive, long-term dig in the Big Horn Basin area (Cloverly Formation
) of Montana and Wyoming
. The expedition was led by John Ostrom
, 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
in Oklahoma
, Paluxy Formation
of Texas
, Wayan Formation
of Idaho
, Cedar Mountain Formation
of Utah
, and Arundel Formation
of Maryland
.
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
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 sub-tropical
to tropical
, with river deltas, flood plains, and forests with swampy inlets reminiscent of modern Louisiana
, 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
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.
. In the arid Little Sheep Mudstone Member, Tenontosaurus is the only herbivorous dinosaur, and it shared its environment with the common predator Deinonychus
as well as an indeterminate species of allosauroid
theropod and goniopholid crocodile. After the major climate shift at the beginning of the Himes Member in the mid-Albian age, several more dinosaurs entered the region, including the less common ornithopod Zephyrosaurus
, the oviraptorosaur
Microvenator
, and an indeterminate species of titanosauriform
sauropod and ornithomimid. The ecological community in the tropical stage also included the small mammal Gobiconodon
, turtle
s such as Glyptops
, and species of lungfish
.
The ecological community was similar in other regions, with dinosaurs like Tenontosaurus and Deinonychus as the most common large vertebrates. In the Antlers Formation
they were joined by the sauropods Astrodon
and Sauroposeidon
, and the allosauroid Acrocanthosaurus
, as well as different lizards, mammals, and fish.
s and tree ferns, cycad
s, and possibly primitive flowering plants. Larger plants and trees were represented by gymnosperm
s, such as conifer and ginkgo
trees. Tenontosaurus was a low browser, and an adult would have had a maximum browsing height of about 3 meters (9 ft) 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.
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
. In all, 20% of Tenontosaurus fossil 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 lack of evidence for coordinated hunting (rather than mobbing behavior as in most modern birds and reptiles) 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. The fact that most Tenontosaurus remains found with Deinonychus are half-grown individuals supports this view.
and shin bone
of one specimen indicates that tenontosaurs used this tissue, today only found in bird
s that are laying eggs, in reproduction. Additionally, like Tyrannosaurus
and Allosaurus
, 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 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.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of medium- to large-sized ornithopod
Ornithopod
Ornithopods or members of the clade Ornithopoda are a group of ornithischian dinosaurs that started out as small, bipedal running grazers, and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world, and dominated the North American...
dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
. The genus is known from the late Aptian to Albian ages of the middle Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
period sediments of western North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, dating between 115 to 108 million years ago. It was formerly thought to be a 'hypsilophodont', but since Hypsilophodontia is no longer considered a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
, it is now considered to be a very primitive iguanodont
Iguanodont
Iguanodonts were herbivorous dinosaurs that lived from the mid-Jurassic to Late Cretaceous. Some members include Camptosaurus, Callovosaurus, Iguanodon, Ouranosaurus, and the hadrosaurids or "duck-billed dinosaurs". Iguanodonts were one of the first groups of dinosaurs to be found...
.
The genus contains two species, Tenontosaurus tilletti (described by John Ostrom
John Ostrom
John H. Ostrom was an American paleontologist who revolutionized modern understanding of dinosaurs in the 1960s, when he demonstrated that dinosaurs are more like big non-flying birds than they are like lizards , an idea first proposed by Thomas Henry Huxley in the 1860s, but which had garnered...
in 1970) and Tenontosaurus dossi (described by Winkler, Murray, 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
Twin Mountains Formation
The Twin Mountains Formation, also known as the Twin Mountain 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 , and is notable for its dinosaur fossils...
of Parker County, Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
.
Description
History of study
The first Tenontosaurus fossil was found in Big Horn County, MontanaMontana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
by an American Museum of Natural History
American Museum of Natural History
The American Museum of Natural History , located on the Upper West Side of Manhattan in New York City, United States, is one of the largest and most celebrated museums in the world...
(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
Barnum Brown , a paleontologist born in Carbondale, Kansas, and named after the circus showman P.T. Barnum, discovered the second fossil of Tyrannosaurus rex during a career that made him one of the most famous fossil hunters working from the late Victorian era into the early 20th century.Sponsored...
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.
During the 1960s, Yale University
Yale University
Yale University is a private, Ivy League university located in New Haven, Connecticut, United States. Founded in 1701 in the Colony of Connecticut, the university is the third-oldest institution of higher education in the United States...
began an extensive, long-term dig in the Big Horn Basin area (Cloverly Formation
Cloverly Formation
The Cloverly Formation are Lower Cretaceous strata located in Montana and Wyoming, in the western United States. The term now includes strata that had formerly been called the Dakota Formation in central and southern Wyoming.-Members:...
) of Montana and Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...
. The expedition was led by John Ostrom
John Ostrom
John H. Ostrom was an American paleontologist who revolutionized modern understanding of dinosaurs in the 1960s, when he demonstrated that dinosaurs are more like big non-flying birds than they are like lizards , an idea first proposed by Thomas Henry Huxley in the 1860s, but which had garnered...
, 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
Antlers Formation
The Antlers Formation occurs as a band of strata from Arkansas through southern Oklahoma into northeastern Texas. It consists of 150 m of silty to sandy mudstones, fine- to coarse grained sandstones that are poorly to moderately sorted and cemented with clay or calcium carbonate...
in Oklahoma
Oklahoma
Oklahoma is a state located in the South Central region of the United States of America. With an estimated 3,751,351 residents as of the 2010 census and a land area of 68,667 square miles , Oklahoma is the 28th most populous and 20th-largest state...
, Paluxy Formation
Paluxy Formation
The Paluxy Formation is a geological formation in Texas whose strata date back to the Early Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.-Vertebrate paleofauna:* ?Ornithomimus sp.* Pleurocoelus cf. nanus...
of Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
, Wayan Formation
Wayan Formation
The Wayan Formation is a geological formation in Idaho whose strata date back to the earliest Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.-Geology and Age:...
of Idaho
Idaho
Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....
, Cedar Mountain Formation
Cedar Mountain Formation
The Cedar Mountain Formation is the name given to distinctive sedimentary rocks in eastern Utah that occur between the underlying Morrison Formation and overlying Naturita Formation . It is composed of non-marine sediments, that is, sediments deposited in rivers, lakes and on flood plains...
of Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...
, and Arundel Formation
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 . This rock unit had been economically important as a source of iron ore, but is now more notable for...
of Maryland
Maryland
Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...
.
Climate
In the Cloverly FormationCloverly Formation
The Cloverly Formation are Lower Cretaceous strata located in Montana and Wyoming, in the western United States. The term now includes strata that had formerly been called the Dakota Formation in central and southern Wyoming.-Members:...
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
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 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...
age), the regions climate was arid
Desert climate
A desert climate , also known as an arid climate, is a climate that does not meet the criteria to be classified as a polar climate, and in which precipitation is too low to sustain any vegetation at all, or at most a very scanty scrub.An area that features this climate usually experiences less than...
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 sub-tropical
Subtropics
The subtropics are the geographical and climatical zone of the Earth immediately north and south of the tropical zone, which is bounded by the Tropic of Cancer and the Tropic of Capricorn, at latitudes 23.5°N and 23.5°S...
to tropical
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
, with river deltas, flood plains, and forests with swampy inlets reminiscent of modern Louisiana
Louisiana
Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...
, 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
Western Interior Seaway
The Western Interior Seaway, also called the Cretaceous Seaway, the Niobraran Sea, and the North American Inland Sea, was a huge inland sea that split the continent of North America into two halves, Laramidia and Appalachia, during most of the mid- and late-Cretaceous Period...
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.
Ecological community
Throughout the Cloverly Formation, Tenontosaurus is by far the most common vertebrate, five times more abundant than the next most common, the ankylosaur SauropeltaSauropelta
Sauropelta is a genus of nodosaurid dinosaur that existed in the Early Cretaceous Period of North America. One species has been named although others may have existed. Anatomically, Sauropelta is one of the most well-understood nodosaurids, with fossilized remains recovered in the U.S. states of...
. In the arid Little Sheep Mudstone Member, Tenontosaurus is the only herbivorous dinosaur, and it shared its environment with the common predator Deinonychus
Deinonychus
Deinonychus was a genus of carnivorous dromaeosaurid dinosaur. There is one described species, Deinonychus antirrhopus. This 3.4 meter long dinosaur lived during the early Cretaceous Period, about 115–108 million years ago . Fossils have been recovered from the U.S...
as well as an indeterminate species of allosauroid
Allosauroidea
Allosauroidea is a superfamily or clade of theropod dinosaurs which contains four families — the Sinraptoridae, Allosauridae, Carcharodontosauridae, and Neovenatoridae...
theropod and goniopholid crocodile. After the major climate shift at the beginning of the Himes Member in the mid-Albian age, several more dinosaurs entered the region, including the less common ornithopod Zephyrosaurus
Zephyrosaurus
Zephyrosaurus is a genus of hypsilophodont ornithopod dinosaur. It is based on a partial skull and postcranial fragments discovered in the Aptian-Albian-age Lower Cretaceous Cloverly Formation of Carbon County, Montana...
, the oviraptorosaur
Oviraptorosauria
Oviraptorosaurs are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot - like skulls, with or without bony crests atop the head...
Microvenator
Microvenator
Microvenator 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, most likely a juvenile, with a living length of about four feet. The adult size of...
, and an indeterminate species of titanosauriform
Macronaria
Macronaria is a clade of sauropod dinosaurs from the Middle Jurassic to Late Cretaceous Periods of what are now North America, South America, Europe, Asia and Africa. The name means 'large nostrils' , in reference to the large nasal openings high on the head that probably supported fleshy...
sauropod and ornithomimid. The ecological community in the tropical stage also included the small mammal Gobiconodon
Gobiconodon
Gobiconodon is an extinct genus of carnivorous mammal. It weighed 10–12 pounds and measured 18-20 inches, and might have resembled a large and robust opossum.-Species:...
, turtle
Turtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
s such as Glyptops
Glyptops
Glyptops is an extinct genus of cryptodire turtle dating from the Late Jurassic and Early Cretaceous periods 155 to 99 m.y.a. Fossils have been found in South Dakota, Wyoming, Colorado, Utah, New Mexico, Oklahoma, and Texas from both the Morrison and Cedar Mountain formations. The type species is G...
, and species of lungfish
Lungfish
Lungfish are freshwater fish belonging to the Subclass Dipnoi. Lungfish are best known for retaining characteristics primitive within the Osteichthyes, including the ability to breathe air, and structures primitive within Sarcopterygii, including the presence of lobed fins with a well-developed...
.
The ecological community was similar in other regions, with dinosaurs like Tenontosaurus and Deinonychus as the most common large vertebrates. In the Antlers Formation
Antlers Formation
The Antlers Formation occurs as a band of strata from Arkansas through southern Oklahoma into northeastern Texas. It consists of 150 m of silty to sandy mudstones, fine- to coarse grained sandstones that are poorly to moderately sorted and cemented with clay or calcium carbonate...
they were joined by the sauropods Astrodon
Astrodon
Astrodon was a genus of large herbivorous sauropod dinosaur, related to Brachiosaurus, that lived in what is now the eastern United States during the Early Cretaceous period. Its fossils have been found in the Arundel Formation, which has been dated through palynomorphs to the Aptian-Albian...
and Sauroposeidon
Sauroposeidon
Sauroposeidon is a genus of sauropod dinosaur known from four neck vertebrae that were found in the southeastern portion of the US state of Oklahoma. The fossils were found in rocks dating to the Early Cretaceous, a period when the sauropods of North America had diminished in both size and...
, and the allosauroid Acrocanthosaurus
Acrocanthosaurus
Acrocanthosaurus is a genus of theropod dinosaur that existed in what is now North America during the Aptian and early Albian stages of the Early Cretaceous. Like most dinosaur genera, Acrocanthosaurus contains only a single species, A. atokensis. Its fossil remains are found mainly in the U.S...
, as well as different lizards, mammals, and fish.
Diet
Plant life in the Tenontosaurus ecosystem was likely dominated by fernFern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s and tree ferns, cycad
Cycad
Cycads are seed plants typically characterized by a stout and woody trunk with a crown of large, hard and stiff, evergreen leaves. They usually have pinnate leaves. The individual plants are either all male or all female . Cycads vary in size from having a trunk that is only a few centimeters...
s, and possibly primitive flowering plants. Larger plants and trees were represented by gymnosperm
Gymnosperm
The gymnosperms are a group of seed-bearing plants that includes conifers, cycads, Ginkgo, and Gnetales. The term "gymnosperm" comes from the Greek word gymnospermos , meaning "naked seeds", after the unenclosed condition of their seeds...
s, such as conifer and ginkgo
Ginkgo
Ginkgo , also spelled gingko and known as the Maidenhair Tree, is a unique species of tree with no close living relatives...
trees. Tenontosaurus was a low browser, and an adult would have had a maximum browsing height of about 3 meters (9 ft) 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 bird-like carnivorous theropod DeinonychusDeinonychus
Deinonychus was a genus of carnivorous dromaeosaurid dinosaur. There is one described species, Deinonychus antirrhopus. This 3.4 meter long dinosaur lived during the early Cretaceous Period, about 115–108 million years ago . Fossils have been recovered from the U.S...
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
Sauropelta is a genus of nodosaurid dinosaur that existed in the Early Cretaceous Period of North America. One species has been named although others may have existed. Anatomically, Sauropelta is one of the most well-understood nodosaurids, with fossilized remains recovered in the U.S. states of...
. In all, 20% of Tenontosaurus fossil 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 lack of evidence for coordinated hunting (rather than mobbing behavior as in most modern birds and reptiles) 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. The fact that most Tenontosaurus remains found with Deinonychus are half-grown individuals supports this view.
Reproduction
The presence of medullary bone tissue in the thigh boneFemur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
and shin bone
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
of one specimen indicates that tenontosaurs used this tissue, today only found in bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s that are laying eggs, in reproduction. Additionally, like Tyrannosaurus
Tyrannosaurus
Tyrannosaurus meaning "tyrant," and sauros meaning "lizard") is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex , commonly abbreviated to T. rex, is a fixture in popular culture. It lived throughout what is now western North America, with a much wider range than other...
and Allosaurus
Allosaurus
Allosaurus is a genus of large theropod dinosaur that lived 155 to 150 million years ago during the late Jurassic period . The name Allosaurus means "different lizard". It is derived from the Greek /allos and /sauros...
, 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 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.