Tenontosaurus

Taxobox
name = "Tenontosaurus"

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image_width = 250px
fossil_range = Early Cretaceous
regnum = Animalia
phylum = Chordata
classis = Sauropsid
superordo = Dinosauria
ordo = Ornithischia
subordo = Cerapoda
infraordo = Ornithopoda
familia = Tenontosauridae
genus = "Tenontosaurus"
subdivision_ranks = Species
subdivision =
* "T. tilletti" Ostrom, 1970 (type)
* "T. dossi" Winkler, Murray & Jacobs, 1997

"Tenontosaurus" (pronEng|tɨˌnɒntəˈsɔrəs ten-ON-toe-SORE-us) is a genus of medium- to large-sized ornithopod dinosaur. 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.

Description

The genus is known from the Aptian to Albian stages of the Early to Middle Cretaceous sediments of western North America, dating to around 125 to 105 million years ago. It was about 6.5 to 8 meters (22 to 27 ft) long and 2.2 meters (7 ft) high, with a mass of somewhere between 1 and 2 tonnes (1 to 2 short tons). Its tail was longer than other members of the family, and it walked on four feet most of the time.

Anatomy

The presence of medullary bone tissue in the thigh bone and shin bone of one specimen indicates that tenontosaurs 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.cite journal |last=Lee |first=Andrew H. |coauthors=and Werning, Sarah |year=2008 |title=Sexual maturity in growing dinosaurs does not fit reptilian growth models |journal=Proceedings of the National Academy of Sciences |volume=105 |issue=2 |pages=582–587 |doi=10.1073/pnas.0708903105]

Discovery and species

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 the Cloverly Formation of Wyoming and Montana, and from the Antlers Formation of southern Oklahoma. "T. dossi" is known from only a handful of specimens collected from the Twin Mountains Formation of Parker County, Texas.

Fossil evidence

"Deinonychus" teeth and a number of skeletons were discovered associated with "Tenontosaurus tilletti" specimens, implying that this dinosaur was hunted and/or scavenged by "Deinonychus".cite journal|last=Maxwell|first=W. D. |coauthors=Ostrom, J.H. |year=1995 |title=Taphonomy and paleobiological implications of "Tenontosaurus"-"Deinonychus" associations|journal=Journal of Vertebrate Paleontology |volume=15 |issue=4 |pages=707–712 ( [http://www.vertpaleo.org/publications/jvp/15-707-712.cfm abstract] )] cite journal|last=Brinkman|first=Daniel L. |coauthors=Cifelli, Richard L., Czaplewski, Nicholas J. |year=1998 |title="First Occurrence of Deinonychus antirrhopus (Dinosauria: Theropoda) from the Antlers Formation (Lower Cretaceous: Aptain-Albian) of Oklahoma"|journal=Oklahoma Geological Survey |issue=164 |pages=27] cite journal|last=Roach|first=B. T.|coauthors=D. L. Brinkman |year=2007 |title=A reevaluation of cooperative pack hunting and gregariousness in "Deinonychus antirrhopus" and other nonavian theropod dinosaurs|journal=Bulletin of the Peabody Museum of Natural History |volume=48 |issue=1 |pages=103–138 |doi=10.3374/0079-032X(2007)48 [103:AROCPH] 2.0.CO;2 |doilabel=10.3374/0079-032X(2007)48[103:AROCPH]2.0.CO;2]

References