Tenontosaurus

*Tenontosaurus tilletti*

* Timothy Bradley Artwork
* Joe Tucciarone Artwork
* Robert F Walters Artwork

***Tenontosaurus*** was an Ornithopod that lived during the Early Cretaceous period in North America. It was mostly prey for *Deinonychus* and *Acrocanthosaurus*.

The three long, sharp claws on its hands would have enabled Tenontosaurus to swipe at a predator.

## Description

*Tenontosaurus* (/tɨˌnɒntɵˈsɔrəs/ te-NON-to-SAWR-əs; meaning "sinew lizard") 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.

## History

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.

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.

## Classification

The cladogram below follows an analysis by Butler *et al*, 2011.

## Paleobiology

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.

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*. 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.[7] 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. It also lived in the same area as the large carnivorous dinosaur *Acrocanthosaurus*.

## 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*. 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*.*

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. 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.[13][14] 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. 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*.[17][18] 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*.

## JPInstitute.com Description

This was an early member of the plant-eating family of dinosaurs that includes Iguanodon. It had a very long tail compared to other members of its family. Instead of front teeth, it had a beak, and it walked on all four feet most of the time.

This dinosaur was originally found as a partial skeleton in 1903. The genus was not named, however, until the early 1960's. By that time parts of more than 20 individuals had been discovered. It had at least 59 caudal vertebrae in its long tail. One specimen was found with Deinonychus teeth associated with it, leading to the conclusion that Tenontosaurus was fed upon by this predator, which probably hunted it in small packs.

## Appearance in other media

### *Jurassic Park*

* In Jurassic Park I the comic, Dr. Alan Grant and Dr. Ellie Sattler had found *Tenontosaurus* fossils and Dr. Grant theorizes that these bones were the last meal of a fossilised pack of *Velociraptor* (which is actually a reclassified *Deinonychus* in this comic series) that they had just uncovered.
* *Tenontosaurus* was planned to appear in the game Jurassic Park: Operation Genesis. For unknown reasons, the development of *Tenontosaurus* was terminated.
* In the *Jurassic Park* novel, Alan Grant mentions *Tenontosaurus* when he is explaining to Ian Malcolm about coordinated attacking behavior in raptors. He states that it would be one of the prey items that *Velociraptor* (reclassified *Deinonychus* in the novels) would hunt and kill.
* *Tenontosaurus* will be in *Jurassic World: Alive* . It inaccurately has a much shorter tail than in life.

## Links

http://web.archive.org/web/20031221151911fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_tenon.html#
https://web.archive.org/web/20080601093747/http://kids.yahoo.com/dinosaurs/46--Tenontosaurus