New Mexico Geological Society Annual Spring Meeting — Abstracts

Intensive excavations totaling 21 days in May and September, 1999, vastly improved our understanding of NMMNH locality 3845, the Snyder Quarry. This locality, situated in the Petrified Forest Formation approximately 28.5 m below the Rock Point Formation, yields diverse and well-preserved assemblages of Upper Triassic vertebrates and invertebrates, and is probably the most important and productive Chinle Group vertebrate fossil locality discovered in the last half of the twentieth century. Taxa added to the faunal list in 1999 include unionid bivalves, as-yet-undetermined osteichthyans, metoposaurid amphibians (probably Buettneria perfecta), and the aetosaur Typothorax coccinarum. Additional material has also made it possible to refine previous taxonomic assignments. A complete skull of "Belodon" buceros, a Pseudopalatus-grade phytosaur, is the first generically determinate phytosaur from the quarry, although at least three other phytosaur skulls await preparation at NMMNH. Additionally, we now have significantly more cranial and postcranial material from the coelophysid theropod than first reported, and tentatively recognize it as a new species of Eucoelophysis. Both Typothorax coccinarum and Pseudopalatus-grade phytosaurs are index taxa of the Revueltian land-vertebrate faunachron, confirming earlier lithostratigraphic correlations that predicted a Revueltian age (early-mid Norian, approximately 218 Ma) for the Snyder Quarry.

The revised faunal list thus includes conchostracans, a decapod crustacean, unionid bivalves, cf. Semionotus, other osteichthyans, aff. Buettneria, "Belodon" buceros, aff. Pseudopalatus, Desmatosuchus haplocerus, Typothorax coccinarum, a ?cynodont, Eucoelophysis n. sp., a larger ceratosaur, and at least one microvertebrate archosaur. Numerically, this is one of the most diverse Chinle sites known. Screenwashing of several tons of matrix from the site will probably yield additional taxa. The quality of vertebrate preservation is exceptional, and preliminary preparation indicates that several ontogenetic stages of phytosaurs are present, as well as at least three individuals of Eucoelophysis. Continued excavation and preparation of fossil material from the Snyder Quarry thus presents a unique opportunity to address diverse questions regarding Upper Triassic ecosystems.