New Mexico Geological Society Annual Spring Meeting — Abstracts

The Trujillo Formation is as much as 68 m of sandstone. mudstone. conglomerate and minor mudrock which crops out widely in West Texas and northeastern New Mexico. Previously, the only fossils from this unit were coelacanth and Semionotus-like scales. megaplant fossils and palynomorphs in Sunday Canyon. Randall County. Texas. Several tetrapod localities have been found recently in the Trujillo in the drainages of Revuelto and Barranca Creeks in Quay County, New Mexico. The Revuelto localities have produced Unio sp., scutes of a derived phytosaur (e. g. not Paleorhinus or Mystriosuchus). a jaw fragment of a small phytosaur. a phytosaur neural spine. a fragment of a paramedian scute of the aetosaur Typothorax sp. a rauisuchian tooth and vertebrate coprolites. The Barranca localities have yielded scutes of a derived phytosaur. a fragment of a small phytosaur rostrum and well-preserved scutes of Typothorax coccinarum. The presence of Typothorax coccinarum suggests an early Norian age for the Trujillo. This age determination is supported by the occurrence of the ?angiosperm Sanmiguelia lewisi in Sunday Canyon and the fact that the Trujillo unconformably overlies strata in east-central New Mexico and West Texas that contain latest Carnian tetrapod faunas. This age determination contradicts interpretations of the age of Trujillo palynomorphs. The high percentage ot' small (presumed juvenile J phytosaur specimens (skull length < 45 cm) in the Trujillo. which are very rare in most Late Triassic faunas (e. g. Bull Canyon Formation which overlies Trujillo). suggests that young phytosaurs may have been ecologically separated from adults. Juvenile phytosaurs may have inhabited perennial streams (e. g. Trujillo) rather than more ephemeral streams (e. g. Bull Canyon Formation). Alternatively. unknown. small phytosaur taxa may have inhibited perennial streams.