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.[1]
Discovery
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".[2] The specific namecrosbyensis, 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 M. Sullivan and Martin Lockley in 1998 and the type species is Caseosaurus crosbyensis.[3]
Classification
Referred ilium
In 1998, Hunt et al., 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 silesauridEucoelophysis, strongly resembles the Caseosaurus holotype.[4] Langer (2004) examined the ilium and reassigned it back to the genus Chindesaurus.[5]
However, in 2018 Caseosaurus was considered a valid species, as a relative of Herrerasaurus outside of the Dinosauria.[6]
Distinguishing anatomical features
According to Baron and Williams (2018), Caseosaurus could be distinguished from all dinosaurs (including herrerasaurids, which fall outside Dinosauria in their analysis) based on the following trait: a sharp, well developed ridge that connects the midpoint of the supracetabular crest to the preacetabular process.[6] However, a recent review of early South American dinosaurs considered it to be a nomen dubium without commenting on the previous study.[7]
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.
^Hunt, A. P., Lucas, S. G., Heckert, A. B., Sullivan, R. M., and Lockley, M. G., 1998, Late Triassic Dinosaurs from the Western United States: Geobios, v. 31, n. 4, p. 511-531.
^Irmis, Nesbitt, Padian, Smith, Turner, Woody and Downs, 2007. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science. 317, 358-361.
^Langer, 2004. Basal Saurischia. In Weishampel, Dodson and Osmolska. The Dinosauria Second Edition. University of California Press. 861 pp.
