The Colorado City Formation is mostly restricted to Howard and Borden counties. The formation hosts the Otis Chalk fossil sites, named after a ghost town in Howard County. Despite their importance, the Otis Chalk localities have been difficult to resolve in the stratigraphy of Triassic Texas.[5] They occupy a narrow band of sediments between the slightly older Camp Springs Formation and much younger Cretaceous deposits.
The first major excavations near Otis Chalk were led by UMMP paleontologists starting in 1927. Several new phytosaur species were discovered during these digs. University of Oklahoma paleontologists followed with their own expedition in 1931. The vast majority of fossils collected from the formation were recovered during a 1939–1941 state-sponsored Works Progress Administration paleontological survey. Several sites southeast of Big Spring were particularly productive. Fossils collected by these efforts were stored at the newly opened Texas Memorial Museum in Austin. Since the 1940s, collection from the Otis Chalk area has been more limited. One notable find is a pond deposit, the Schaeffer Fish Quarry, discovered in 1967 by AMNH paleontologist Bobb Schaeffer.[4]
The Otis Chalk localities that are situated in the Colorado City Formation form the basis of the OtischalkianLand Vertebrate Faunachron (LVF), which is defined by the first appearance of Parasuchus.[6]
Postcranial bones of an unusual bipedal archosaur related to poposaurids.[4] Later determined to be synonymous with Shuvosaurus, a shuvosauridpoposauroid initially misidentified as a theropod dinosaur.[9]
Most Otis Chalk desmatosuchin aetosaur fossils have been referred to Longosuchus or Lucasuchus, but a few have been referred to Desmatosuchus (Episcoposaurus) haplocerus.[4] The modern valid combination for this species is Desmatosuchus spurensis.[12]
A common mystriosuchine phytosaur. Some sources refer all Otis Chalk Angistorhinus material to "Angistorhinus megalodon",[4] while most other sources support affinities with the type species Angistorhinus grandis from Wyoming.[16]
A carnivorous azendohsauridallokotosaurian in the subfamily Malerisaurinae. Regarded as a chimera by Spielmann et al. (2006),[20] but treated as valid by other sources.[18][19] Numerous disarticulated Malerisaurus-like fossils are also known from Quarry 1 (TMM 31025).[19]
A dubious putative rhynchosaur, likely synonymous with Malerisaurus langstoni.[19] Supposed premaxilla fossils have been reinterpreted as metoposaurid cleithra.[19] Femora and humeri previously referred to this species likely belong to Trilophosaurus[4] or Malerisaurus[19] instead.
^Lucas, S. G., Hunt, A. P., Heckert, A. B., and Spielmann, J. A., (2007) Global Triassic tetrapod biostratigraphy and biochronology: 2007 status: New Mexico Museum of Natural History and Science Bulletin, v. 41 (The Global Triassic), p. 229- 240.
^Nesbitt, S. (2007). "The anatomy of Effigia okeeffeae (Archosauria, Suchia), theropod-like convergence, and the distribution of related taxa." Bulletin of the American Museum of Natural History, 302: 84 pp. http://digitallibrary.amnh.org/dspace/handle/2246/5840
^ abcNesbitt, Sterling J.; Irmis, Randall B.; Parker, William G.; Smith, Nathan D.; Turner, Alan H.; Rowe, Timothy (2009). "Hindlimb osteology and distribution of basal dinosauromorphs from the Late Triassic of North America". Journal of Vertebrate Paleontology. 29 (2): 498–516. doi:10.1671/039.029.0218. S2CID34205449.
^ abcdeWilson, John Andrew (1948). "A Small Amphibian from the Triassic of Howard County, Texas". Journal of Paleontology. 22 (3): 359–361. JSTOR1299405.
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