Caseosaurus

*Caseosaurus crosbyensis*

***Caseosaurus*** (/ˌkeɪziːɵˈsɔrəs/ KAY-zee-o-SAWR-əs) is a genus of herrerasaurid theropod dinosaur that lived approximately 235 to 228 million years ago during the latter part of the Triassic Period in what is now Texas, in North America. *Caseosaurus* was a small, lighly-built, bipedal, ground-dwelling carnivore, that could grow up to 2 m (6.6 ft) long.

## Description

The genus Caseosaurus, is known from specimen UMMP 8870, an isolated hip bone that measures nearly 141 mm. A 3D model of this specimen is available on the University of Michigan Online Repository of Fossils. Size estimates suggest that Caseosaurus was at best 2 m (6.6 ft) long and weighed 50 kilograms (110.2 pounds) at most.

## Etymology

The genus name *Caseosaurus*, means "Case's lizard", and was named in the honor of the scientist who discovered it, Ermine Cowles Case. The Greek suffix "-saurus" (σαυρος) means "lizard". The specific name crosbyensis, is a Latinized rendering of Crosby County in Texas, the site of its discovery. *Caseosaurus* was described and named by A. P. Hunt, Spencer G. Lucas, Andrew B. Heckert, Robert Sullivan and Martin Lockley in 1998 and the type species is *Caseosaurus crosbyensis*.

## Classification

In 1998, Hunt et al. (1998), examined UMMP 8870, a partial hip bone (ilium) that was assigned as a paratype of the dinosaur *Chindesaurus* and made it the holotype of a new dinosaur, *Caseosaurus crosbyensis*. Irmis et al. concluded that an ilium, NMMNH P-35995 originally assigned by Heckert et al., in 2000 to the dinosaur *Eucoelophysis*, strongly resembles the *Caseosaurus* holotype. *Caseosaurus* has also been classified as a relative of *Herrerasaurus*. Langer (2004) examined the ilium and re-assigned it back to the genus *Chindesaurus*. Other paleontologists also agree that this may be the same dinosaur as *Chindesaurus*, which lived during the same period and geological region.

### Distinguishing anatomical features

A diagnosis is a statement of the anatomical features of an organism (or group) that collectively distinguish it from all other organisms. Some, but not all, of the features in a diagnosis are also autapomorphies. An autapomorphy is a distinctive anatomical feature that is unique to a given organism or group.

According to Hunt et al. (1998), *Caseosaurus* could be distinguished based on the following features:

* a shallow brevis shelf is present on the ilium
* a medial longitudinal ridge that is more ventrally placed
* a transversely thinner postacetabular blade is present

## Paleoecology

The only specimen of Caseosaurus was discovered in the Tecovas Formation of the Dockum Group in Texas, in sediments deposited during the Norian stage of the Late Triassic period, approximately 221.5 to 212 million years ago. Caseosaurus's paleoenvironment included the archosaur Tecovasaurus and other early theropod dinosaurs, some of whom left bipedal tracks that were preserved.

## JPInstitute.com Description

This small meat-eater would have been one of the very first dinosaurs to live in North America. It is very similar to Herrerasaurus, the early dinosaur found in South America. Very little of this dinosaur was discovered so almost nothing is known of this creature. It would have been very similar looking to all the other early dinosaurs: small, with a long, flexible neck, long arms, a swift runner and a mouthful of sharp teeth.

All of the earliest dinosaurs, regardless of their diet, shared a very similar body style and size. The fragmentary remains don't provide much information about this animal other than age and its similarity to Herrerasaurus. The important thing is that it lived in North America at the beginning of the dinosaur age.

## Links

https://web.archive.org/web/20030803052310fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_caseo.html