The type area of the formation is situated in Garza County, Texas, southeast of Lubbock. The Cooper Canyon Formation consist of reddish siltstone and mudstone with lenses of sandstone and conglomerate. Thickness of the formation in the type area is 161.5 meters. It increases to the south, and in some places exceeds 200 m. The formation contains diverse fossils, including vertebrate remains.[2]
Regional equivalents
The Bull Canyon Formation in eastern New Mexico is equivalent to the upper part of the Cooper Canyon Formation. Some researchers argue that the latter name should be abandoned.[2] The middle and lower parts of the Cooper Canyon are correlated to the Trujillo and Tecovas formations (respectively) further north in the Texas Panhandle. The lowermost part of the Cooper Canyon Formation may also be correlated to the Colorado City Formation further south at Otis Chalk (Howard County).[3][4][5]
Skull and postcranial skeleton (specimen TTUP 9425).[10][8]
Specimens currently only described in unpublished theses, initially referred to a new informal genus "Macysuchus".[10] Referred to R. gregorii by Spielmann and Lucas (2012).[8]
Several skulls and partial skeletons, osteoderms[13]
An armoured aetosaur with large shoulder spines. Type locality of D. smalli, species also known from the Chinle Formation. Some skeletal postcranial material may belong to Paratypothorax.[12]
A large predatory rauisuchid, type specimen from the Post Quarry. Most rauisuchid material from elsewhere in the southwestern US has also been assigned to Postosuchus kirkpatricki but it is unclear how much of it definitively belongs to Postosuchus.[16] A fifth metatarsal from the Boren Quarry (MOTT 3869) may belong to Postosuchus.[15]
Originally named as an ornithomimid dinosaur based on its skull, later recognised to be synonymous with poposauroid postcrania named "Chatterjeea elegans". Type specimen is from the Post Quarry, Shuvosaurus has also reported from the Chinle Formation.
Numerous bones from ornithodirans have been discovered throughout the Cooper Canyon Formation but cannot be assigned to specific genera or clades. However, they are at least variably identifiable as lagerpetids, dinosauromorphs, dinosaurs, saurischians and theropods.[17]
A Malerisaurus-like taxon, a small carnivorous azendohsaurid allokotosaur. Three dentaries from the Boren Quarry were misinterpreted as the oldest saurischian dinosaurs in North America, but show affinity to malerisaurines.[21][22]
Herbivorous trilophosauridallokotosaurs. Of the three species represented in the Boren Quarry, T. dornorum and T. jacobsi are the more common, with T. buettneri represented by only two specimens.[3]T. jacobsi is also common at the Kahle Quarry (NMMNH L-3775) should it belong to the middle Cooper Canyon Formation.[23]
An unusual armoured semi-aquatic archosauriform. Additional limb bones from the Post and Kirkpatrick quarries may belong to Vancleavea or a related taxon.
Other amniotes
Numerous fragmentary limb bones of various reptiles have been collected that cannot be reliably diagnosed to specific clades, though some show similarities to drepanosauromorphs. Indeterminate procolophonid material is known from the Boren Quarry (MOTT 3869).[11]
Miscellaneous amniotes of the Cooper Canyon Formation
Named as a new species of Pachygenelus by Chatterjee (1983), assignment to this genus is doubtful. Material now provisionally regarded as eucynodont.[4]
^ abcdefghijklmnopqrstuvwxyzaaabacadaeafagahaiajakalamanaoapaqarasatauavawaxayazbabbbcbdMartz, J. W.; Mueller, B.; Nesbitt, S. J.; Stocker, M. R.; Parker, W. G.; Atanassov, M.; Fraser, N.; Weinbaum, J.; Lehane, J. (2013). "A taxonomic and biostratigraphic re-evaluation of the Post Quarry vertebrate assemblage from the Cooper Canyon Formation (Dockum Group, Upper Triassic) of southern Garza County, western Texas". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 103 (3–4): 339–364. doi:10.1017/S1755691013000376. S2CID129744424.
^ abcdefghijklHungerbühler, Axel; Mueller, Bill; Chatterjee, Sankar; Cunningham, Douglas P. (September 2012). "Cranial anatomy of the Late Triassic phytosaur Machaeroprosopus , with the description of a new species from West Texas". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 103 (3–4): 269–312. doi:10.1017/S1755691013000364. S2CID129442164.
^ abcdReyes, W. A.; Martz, J. W.; Small, B. J. (2024). "Garzapelta muelleri gen. et sp. nov., a new aetosaur (Archosauria: Pseudosuchia) from the Late Triassic (middle Norian) middle Cooper Canyon Formation, Dockum Group, Texas, USA, and its implications on our understanding of the morphological disparity of the aetosaurian dorsal carapace". The Anatomical Record. 307 (4): 1271–1299. doi:10.1002/ar.25379.
^ abSarigül, V. (2017). "New archosauromorph fragments from the Dockum Group of Texas and the assessment of earliest dinosaurs in North America". Historical Biology. 30 (8): 1059–1075. doi:10.1080/08912963.2017.1333609.
^ abcSmall, Bryan J. (15 December 1997). "A new procolophonid from the Upper Triassic of Texas, with a description of tooth replacement and implantation". Journal of Vertebrate Paleontology. 17 (4): 674–678. doi:10.1080/02724634.1997.10011016.
^Witmer, L. (2002). "The debate on avian ancestry: phylogeny, function, and fossils". In Chiappe, L. M.; Witmer, L. M. (eds.). Mesozoic birds: Above the heads of dinosaurs. Berkeley, Calif., USA: University of California Press. pp. 3–30. ISBN0-520-20094-2.
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