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

Abstract

The Post Quarry, within the lower part of the type section of the Upper Triassic Cooper Canyon Formation in southern Garza County, western Texas, contains a remarkably diverse vertebrate assemblage. The Post Quarry has produced: the small temnospondylRileymillerus cosgriffi; the metoposauridApachesaurus gregorii; possible dicynodonts and eucynodonts; a clevosaurid sphenodontian; non-archosauriform archosauromorphs (Trilophosaurus dornorum, simiosaurians, and possiblyMalerisaurus); the phytosaurLeptosuchus; several aetosaurs (Calyptosuchus wellesi,Typothorax coccinarum,Paratypothorax, andDesmatosuchus smalli); the poposauroidShuvosaurus inexpectatus(“Chatterjeea elegans”); the rauisuchidPostosuchus kirkpatricki; an early crocodylomorph; several dinosauromorphs (the lagerpetidDromomeron gregorii, the silesauridTechnosaurus smalli, a herrerasaurid, and an early neotheropod); and several enigmatic small diapsids. Revised lithostratigraphic correlations of the lower Cooper Canyon Formation with the Tecovas Formation, the occurrence ofLeptosuchus, and the overall composition of the assemblage indicate that the Post Quarry falls within the Adamanian biozone, and not the Revueltian biozone. Stratigraphic subdivision of the Adamanian biozone may be possible, and the Post Quarry may be correlative with the upper part of the Adamanian biozone in Arizona. The age of the Post Quarry assemblage is possibly late Lacian or earliest Alaunian (late early Norian or earliest middle Norian), between 220 and 215 Ma.

New trilophosaurid species demonstrates a decline in allokotosaur diversity across the Adamanian-Revueltian boundary in the Late Triassic of western North America

“…Thus, the entire biostratigraphic ranges of T. dorno rum, T. buettneri, and T. jacobsi are contained within the Otischalkian and Adamanian estimated holochronozones. No previously reported trilophosaurid species spans the Adamanian-Revueltian boundary (parker & Martz 2011;Martz et al 2013), and T. phasmalophos represents the youngest and only unambiguous Revueltian trilophosaurid. A single worn tricuspid tooth was documented from the Owl Rock Member of the Chinle Formation on Ward's Terrace in Arizona (MNA V7064; kirBy 1991) and may represent any number of coeval non-trilophosaurid taxa that exhibit similar tooth morphologies (heckert et al 2006).…”

“…The presence of five cingula in T. phasmalophos, the known specimens of which are much smaller than the holotype of T. dornorum, refutes this hypothesis of a simple relationship between number of cingula and specimen size in trilophosaurids. For these reasons we follow Martz et al (2013) in treating T. jacobsi and T. dornorum as distinct taxa.…”

“…Those Trilopho saurus buettneri localities occur in the type Otischalkian strata, which are characterized by the non-Mystriosuchinae phytosaurian Parasuchus (=Paleorhinus; stocker 2010, 2013a, 2013b; Butler et al 2014;kaMMerer et al 2015). Trilophosaurus buettneri occurs in other places within the Dockum Group of Texas and the Chinle Formation of Arizona (see spielMann et al 2007spielMann et al , 2008 for a discussion and also Martz 2008;Martz et al 2013;stocker 2013a;sarigül 2016, 2017a, 2017blessner et al 2018;Marsh 2018 for revisions and synthesis of the stratigraphic relationships of the Dockum Group). However, the highest occurrence of isolated teeth of Trilophosaurus buettneri occurs at sites within the upper part of the Blue Mesa Member at PEFO, including PFV 122/PFV 181 (the Dying Grounds), that are Adamanian due to their occurrence above the lowest occurrence of the non-Mystriosuchini leptosuchomorph phytosaurs (parker & Martz 2011;stocker 2012;Martz & parker 2017).…”

“…Spino suchus caseanus is found at the Placerias Quarry within the Lot's Wife beds of the Sonsela Member (Chinle Formation) in Arizona (UCMP A269, which also contains T. jacobsi;spielMann et al 2007spielMann et al , 2008nesBitt et al 2015) as well as the Kahle Quarry (see above), both of which are Adamanian. Another species of Trilopho saurus, T. dorno rum (Mueller & parker 2006), is found at the Post Quarry (MOTT 3624) in the top of the lower unit of the Cooper Canyon Formation of Garza County, Texas (Martz 2008;Martz et al 2013), and at Lott Hill (MOTT 3878) and the Boren Quarry (MOTT 3869) in the lower part of the Cooper Canyon Formation (Mueller & parker 2006;Martz 2008). Chinle Formation occurrences of T. dorno rum include its type locality in the Lot's Wife beds of the Sonsela Member at PEFO (PFV 191;Mueller & parker 2006;parker & Martz 2011) and a locality in the lower part of the Jim Camp Wash beds of the Sonsela Member at PFV 414 (PEFO 42365/ UWBM 116791;siDor et al 2018).…”

Anatomical notes and discussion of the first described aetosaurStagonolepis robertsoni(Archosauria: Suchia) from the Upper Triassic of Europe, and the use of plesiomorphies in aetosaur biochronology

“…A distinct posterior centrodiapophyseal lamina (Wilson, 1999) stretches from the base of the transverse process to the posterior portion of the neurocentral suture. This is the “T-beam” structure described by Case (1922) for the posterior cervical and dorsal vertebrae of Desmatosuchus spurensis and described as present in S. robertsoni (Walker, 1961) and Typothorax (Martz, 2002) and also occurs in Paratypothorax (Martz et al., 2013 Fig. 9D).…”