The vertebrate fauna of the Upper Triassic (Revueltian: Early-Mid Norian) Painted Desert Member (Petrified Forest Formation: Chinle Group) in the Chama Basin, northern New Mexico

Abstract

The Upper Triassic Painted Desert Member of the Petrified Forest Formation in north-central New Mexico yields one of the most extensive and significant Revueltian (early-mid Norian) tetrapod faunas known. Particularly significant aspects of this fauna are: (1) its long history of collection and study, including designation of important type specimens; and (2) the richness of the unit, including no fewer than three major vertebrate quarries (the Canjilon, Snyder, and Hayden quarries). Beginning with the work of Cope and extending to the present day, the bulk of the Triassic vertebrates recovered from the Chama Basin have been derived from the Painted Desert Member. This includes tetrapod faunas collected at Gallina, Orphan Mesa, and the Canjilon, Snyder, and Hayden quarries. Although any one of these localities can be exceptionally rich, the Painted Desert Member fauna in the Chama Basin is a relatively low-diversity assemblage dominated by the phytosaur Pseudopalatus and the aetosaur Typothorax. The vast majority of the known diversity of the unit in the Chama Basin was derived from a single locality, the Snyder quarry. We also review the stratigraphic and biostratigraphic evidence that suggest that this fauna may be slightly younger (Lucianoan) than the type Revueltian (Barrancan) assemblage, although this argument is weakened by the fact that it is based at least in part on the absence of characteristic Revueltian (Barrancan) taxa such as Revueltosaurus callenderi.