Tenontosaurus | |
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T. dossi on exhibit in the Perot Museum of Nature and Science | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | † Ornithischia |
Clade: | † Ornithopoda |
Clade: | † Iguanodontia |
Genus: | † Tenontosaurus Ostrom, 1970 |
Species | |
Tenontosaurus ( /tɪˌnɒntəˈsɔːrəs/ ti-NON-tə-SOR-əs; lit. 'sinew lizard') is a genus of iguanodontian ornithopod dinosaur. 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 to Albian ages of the Early Cretaceous period sediments of western North America, dating between 115 and 108 million years ago. It contains two species, Tenontosaurus tilletti (described by John Ostrom in 1970 [1] ) and Tenontosaurus dossi (described by Winkler, Murry, and Jacobs in 1997). [2] 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.
The first Tenontosaurus fossil was found in Big Horn County, Montana 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. [3]
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, [4] 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. [3]
Tenontosaurus was a medium-sized ornithopod, with both species weighing about 1,000 kilograms (2,200 lb). Paul in 2016 estimated that T. tilletti would have been 6 metres (20 ft) and weighed 600 kilograms (1,300 lb), [5] but Campione and Evans in 2020 estimated that this species would have weighed up to 971–1,019 kilograms (2,141–2,247 lb). [6] Paul also estimated that T. dossi would have been 7 meters (23 ft) long and weighed 1,000 kilograms (2,200 lb). [5]
Tenontosaurus was a facultative quadruped, capable of assuming either a bipedal or quadrupedal stance. It may have used a quadrupedal stance while feeding, [4] [7] but was probably incapable of rapid quadrupedal movement. [4] Tenontosaurus resembles quadrupedal ornithischians in having a tibia that is shorter than the femur and an anterolateral process on the ulna, but it resembles bipedal ornithischians in having a relatively narrow pelvis and a pendant fourth trochanter. [7] The manus (the hand/front foot) shows a mixture of traits associated with bipeds and quadrupeds. It retains narrow claws, unlike the hoof-like unguals of quadrupedal ornithischians, [7] [8] has a short metacarpus, as in the bipedal Hypsilophodon, and retains grasping adaptations. However, the phalanges are also shortened as an adaptation to weight bearing. [8] An analysis of the overall proportions and center of mass of Tenontosaurus found it to be a quadruped, although the analysis only distinguished bipeds from quadrupeds without including a facultatively bipedal category. [9]
The cladogram below follows an analysis by Butler et al, 2011. [10]
Ornithopoda |
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Plant life in the Tenontosaurus ecosystem was likely dominated by ferns and tree ferns, cycads, and possibly primitive flowering plants. Larger plants and trees were represented by gymnosperms, 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 (10 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. [3]
Teeth and a number of skeletons belonging to the carnivorous theropod Deinonychus 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 . [11] 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 [12] ) as well as evidence that Deinonychus may have been cannibalizing each other, as well as the Tenontosaurus, in a feeding frenzy. [13] 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. [3] [14] It also lived in the same area as the large carnivorous dinosaur Acrocanthosaurus . [15]
The presence of medullary bone tissue in the thigh bone and shin bone of one specimen indicates that Tenontosaurus used this tissue, today only found in birds 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. [16] A histological study showed that T. tilletti grew quickly early in life and during sub-adult ontogeny, but grew very slowly in the years approaching maturity, unlike other iguanodontians. [17]
Throughout the Cloverly Formation, Tenontosaurus is by far the most common vertebrate, five times more abundant than the next most common, the ankylosaur Sauropelta . [18] 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 , turtles such as Glyptops , and species of lungfish . [3]
The ecological community was similar in other regions, with dinosaurs like Tenontosaurus and Deinonychus as the most common large vertebrates. The Antlers Formation 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. [19] The area preserved in this formation was a large floodplain that drained into a shallow inland sea. Several million years later, this sea would expand to the north, becoming the Western Interior Seaway and dividing North America in two for nearly the entire Late Cretaceous period. The paleoenvironment of the Antlers Formation consisted of tropical or sub-tropical forests, floodplains, river deltas, coastal swamps, bayous and lagoons, probably similar to that of modern-day Louisiana. [19] [3] In the Antlers Formation in what is now Oklahoma, Tenontosaurus and Deinonychus shared their paleoenvironment with other dinosaurs, such as the sauropods Astrodon (Pleurocoelus) and Sauroposeidon proteles, and the carnosaur Acrocanthosaurus atokensis, which was likely the apex predator in this region. [20] [14] The most common dinosaur in the paleoenvironment preserved in this formation is Tenontosaurus. Other vertebrates present at the time of Tenontosaurus included the amphibian Albanerpeton arthridion, the reptiles Atokasaurus metarsiodon and Ptilotodon wilsoni, the crurotarsan reptile Bernissartia , the cartilaginous fish Hybodus buderi and Lissodus anitae, the ray-finned fish Gyronchus dumblei, the crocodilian Goniopholis , and the turtles Glyptops and Naomichelys. [21] [22] Possible indeterminate bird remains are also known from the Antlers Formation. The fossil evidence suggests that the gar Lepisosteus was the most common vertebrate in this region. The early mammals known from this region include Atokatherium boreni and Paracimexomys crossi. [23]
In the Cloverly Formation 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. [3]
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 subtropical to tropical, with river deltas, floodplains, and forests with swampy inlets reminiscent of modern Louisiana, though marked dry seasons persisted to create savannah-like environments as well. [19] 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. [3]
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. [3]
Deinonychus is a genus of dromaeosaurid theropod dinosaur with one described species, Deinonychus antirrhopus. This species, which could grow up to 3.4 meters (11 ft) long, lived during the early Cretaceous Period, about 115–108 million years ago. Fossils have been recovered from the U.S. states of Montana, Utah, Wyoming, and Oklahoma, in rocks of the Cloverly Formation and Antlers Formation, though teeth that may belong to Deinonychus have been found much farther east in Maryland.
Sauroposeidon 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 Oklahoma, Wyoming, and Texas.
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, Acrocanthosaurus contains only a single species, A. atokensis. It had a continent-wide range, with fossil remains known from the U.S. states of Oklahoma, Texas, and Wyoming in the west, and Maryland in the east.
John Harold Ostrom was an American paleontologist who revolutionized the modern understanding of dinosaurs. Ostrom's work inspired what his pupil Robert T. Bakker has termed a "dinosaur renaissance".
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 Wyoming, Montana, and possibly Utah. It is also the earliest known genus of nodosaurinae; most of its remains are found in a section of the Cloverly Formation dated to 108.5 million years ago.
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 length of 1.3 m (4.3 ft), and consequently, the adult size remains uncertain. Microvenator celer is primitive and may be the "sister taxon to all other oviraptorosaurs."
Astrodon is a genus of large herbivorous sauropod dinosaur, measuring 20 m (66 ft) in length, 9 m (30 ft) in height and 20 metric tons in body mass. It lived in what is now the eastern United States during the Early Cretaceous period, and fossils have been found in the Arundel Formation, which has been dated through palynomorphs to the Albian about 112 to 110 million years ago.
Albertosaurines, or dinosaurs of the subfamily Albertosaurinae, lived in the Late Cretaceous of United States and Canada. The subfamily was first used by Philip J. Currie, Jørn H. Hurum, and Karol Sabath as a group of tyrannosaurid dinosaurs. It was originally defined as "(Albertosaurus + Gorgosaurus)", including only the two genera. The group is the sister clade to Tyrannosaurinae. In 2007, it was found that the group also contained Maleevosaurus, often synonymized with Tarbosaurus. However, this classification has not been accepted and Maleevosaurus is still considered a juvenile Tarbosaurus or Tyrannosaurus.
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 in northern Emery County, Utah, where William Lee Stokes first studied the exposures in 1944.
The Cloverly Formation is a geological formation of Early and Late Cretaceous age that is present in parts of Montana, Wyoming, Colorado and Utah in the western United States. It was named for a post office on the eastern side of the Bighorn Basin in Wyoming by N.H. Darton in 1904. The sedimentary rocks of formation were deposited in floodplain environments and contain vertebrate fossils, including a diverse assemblage of dinosaur remains. In 1973, the Cloverly Formation Site was designated as a National Natural Landmark by the National Park Service.
The Antlers Formation is a stratum which ranges from Arkansas through southern Oklahoma into northeastern Texas. The stratum is 150 m (490 ft) thick consisting of silty to sandy mudstone and fine to coarse grained sandstone that is poorly to moderately sorted. The stratum is cemented with clay and calcium carbonate. In places the sandstone may be conglomeratic or ferruginous.
The Eumeralla Formation is a geological formation in Victoria, Australia whose strata date back to the Early Cretaceous. It is Aptian to Albian in age. Dinosaur remains are among the fossils that have been recovered from the formation, particularly from the Dinosaur Cove locality.
Paleontology in Oklahoma refers to paleontological research occurring within or conducted by people from the U.S. state of Oklahoma. Oklahoma has a rich fossil record spanning all three eras of the Phanerozoic Eon. Oklahoma is the best source of Pennsylvanian fossils in the United States due to having an exceptionally complete geologic record of the epoch. From the Cambrian to the Devonian, all of Oklahoma was covered by a sea that would come to be home to creatures like brachiopods, bryozoans, graptolites and trilobites. During the Carboniferous, an expanse of coastal deltaic swamps formed in areas of the state where early tetrapods would leave behind footprints that would later fossilize. The sea withdrew altogether during the Permian period. Oklahoma was home a variety of insects as well as early amphibians and reptiles. Oklahoma stayed dry for most of the Mesozoic. During the Late Triassic, carnivorous dinosaurs left behind footprints that would later fossilize. During the Cretaceous, however, the state was mostly covered by the Western Interior Seaway, which was home to huge ammonites and other marine invertebrates. During the Cenozoic, Oklahoma became home to creatures like bison, camels, creodonts, and horses. During the Ice Age, the state was home to mammoths and mastodons. Local Native Americans are known to have used fossils for medicinal purposes. The Jurassic dinosaur Saurophaganax maximus is the Oklahoma state fossil.
The Trinity Group is a group in the Lower Cretaceous lithostratigraphy of Texas, Arkansas, Mississippi, Louisiana and Oklahoma. It is named for the Trinity River of Texas.
This timeline of dromaeosaurid research is a chronological listing of events in the history of paleontology focused on the dromaeosaurids, a group of sickle-clawed, bird-like theropod dinosaurs including animals like Velociraptor. Since the Native Americans of Montana used the sediments of the Cloverly Formation to produce pigments, they may have encountered remains of the dromaeosaurid Deinonychus hundreds of years before these fossils came to the attention of formally trained scientists.
Paramacellodidae is an extinct family of lizards that first appeared in the Middle Jurassic around 170 million years ago (Ma) and became extinct at the end of the Cretaceous around 66 Ma. It was one of the earliest groups of lizards to have undergone an evolutionary radiation, with members found across the supercontinent Laurasia. The phylogenetic relationships and constituent species of Paramacellodidae are uncertain. Many studies regard them to be scincomorphs, a large group that includes skinks and their closest extinct relatives, and possibly also to Cordyoidea, a group that includes spinytail lizards and relatives. Like modern skinks, paramacelloidids had rectangular bony plates called osteoderms covering most of their bodies, including their backs, undersides, and tails. They also had short and robust limbs. Paramacellodids are distinguished from other lizards by the combination two traits in their dentition, the teeth are labiolingually expanded at their bases, and the tooth apices are lingually concave.
Atokasaurus is an extinct genus of scincomorph lizard from the Early Cretaceous of Oklahoma. The type and only species is Atokasaurus metarsiodon, named in 2002 on the basis of a single isolated lower jaw bone found within the Antlers Formation in Atoka County. It is similar in appearance to extinct lizards in the family Paramacellodidae and may itself be a paramacellodid, although the phylogenetic relationships of the group are uncertain. Atokasaurus differs from other paramacellodids in having teeth in the lower jaw with enlarged bases and an S-shaped profile when viewed edge-on.
Ptilotodon is an extinct genus of teiid lizard from the Early Cretaceous of Oklahoma. The type and only known species is Ptilotodon wilsoni, named in 2002 on the basis of a single lower jaw with four teeth found in the Antlers Formation. The small size of the specimen may be an indication that it belonged to a juvenile.
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