New Mexico Geological Society Annual Spring Meeting — Abstracts

We report here a diverse microvertebrate fauna from New Mexico Museum of Natural History and Science (NMMNH) locality 1171 in the Upper Triassic Garita Creek Formation of the Chinle Group near Lamy, Santa Fe County, New Mexico. Vertebrate fossils from this locality include sarcopterygian fish, temnospondyl amphibians, procolophonids, cynodonts?, and archosaurs. Sarcopterygians are represented by toothplates of the dipnoan Arganodus. Amphibian remains include numerous elements, particularly centra, that probably pertain to the metoposaurid temnospondyl Buettneria. Maxillary or dentary teeth of procolophonids have two cusps, one (lingual?) larger than the other (labial?). Possible cynodonts are represented by numerous postcanine teeth. Archosaurs in the fauna include the first Chinle occurrence of the omithischian dinosaurs Pekinosaurus and aff. Galtonia, as well as a larger morph that resembles Revueltosaurus. A single, small (3 mm wide) atlas with dual facets for the articulation of occipital condyles could conceivably belong to either a lissamphibian (frog, salamander, or caecilian) or mammal, and would mark an extremely early representative of either group. However, this element could also pertain to a temnospondyl amphibian. Omithischian dinosaur teeth from NMMNH locality 1171 possess a basal constriction between crown and root, denticles oriented obliquely to the tooth margin, and are asymmetric in mesio-distal views. Teeth assigned to Pekinosaurus are broad and low (crowns nearly as antero-posteriorly long as tall) and leafshaped with closely compressed, fine denticles. Teeth assigned to aff. Galtonia are taller and triangular in labial or lingual view, with a prominent labial bulge and coarser denticles confined to laterally compressed ridges anterior and posterior to the bulge. Larger omithischian tooth crowns from NMMNH locality 1171 are 5-10 mm tall, triangular in labial or lingual view, and bear coarse denticles. These teeth are broadly similar to teeth of Revueltosaurus and are extremely similar to teeth referred to Revueltosaurus by Long and Murry (1995, NMMNH Bull.4) from the lower Chinle Group in the vicinity of St. Johns. This fauna is clearly important because it yields a number of otherwise rare tetrapods of Adamanian (latest Carnian) age. The occurrence of Pekinosaurus and Galtonia facilitate correlation of the Garita Creek Formation to the Newark Supergroup, but also represent a range extension from the Otischalkian to the Adamanian for Pekinosaurus. Dinosaurs are more common in the Chinle Group than previously thought, but are often recovered only as a result of screenwashing methods.