New Mexico Geological Society Annual Spring Meeting — Abstracts

Recent collecting by volunteer crews from the New Mexico Museum of Natural History (NMMNH) at the Snyder Quarry in the upper part of the Petrified Forest Formation, Chinle Group, near Ghost Ranch, New Mexico, has brought to light numerous scutes of the aetosaur Desmatosuchus haplocerus, including a right lateral fourth cervical scute (NMMNH P-29045). The scutes display several diagnostic characteristics of D. haplocerus, including: prolonged thin laminae of bone issuing anteriorly from the scute's anterior edge, lack of an anterior bar, and recurved dorsal spikes on the lateral scutes. These scutes are found in close association with scutes and bones of the aetosaur Typothorax, and bones of phytosaurs and coelophysid theropods.

Of significance is the age of these fossils. Desmatosuchus is most abundant in upper Carnian rocks, with rare occurrences in Norian strata. The Snyder Quarry is stratigraphically very high in the Chinle Group, approximately 60 m below the Entrada Sandstone, and, based on tetrapod biochronology (aetosaur Typothorax and phytosaur Pseudopalatus), the site is Revueltian (early to mid Norian, 210-218 Ma) in age. The Desmatosuchus fossils found at Snyder Quarry are the youngest specimens found and extend the range of Desmatosuchus well into the Norian. It should thus be noted that Desmatosuchus is a poor index taxon, although there is a distinct possibility that there are multiple, temporally successive species that have gone unrecognized due to poor
preservation.