New Mexico Geological Society Annual Spring Meeting — Abstracts

Isolated teeth provide the primary evidence for the presence of small theropod dinosaurs in the Late Cretaceous of the San Juan Basin, northwestern New Mexico. Specimens are from the Santonian Point Lookout Sandstone, the lower Campanian Menefee Formation, the upper Campanian Fruitland and lower Kirtland Formation (Hunter Wash and De-na-zin members), and the upper Maastrichtian Naashoibito Member, Kirtland Formation. We grouped the teeth into several morphotypes, which are assigned to higher level theropod clades. Principal components analysis and discriminate function analysis were used to test for differences between New Mexican morphotypes and those documented from other geographic areas.

Small teeth of Tyrannosauroidea are recovered from all but the Menefee Formation and many likely represent teeth of juvenile individuals. Two dromaeosaurid morphotypes were identified; one resembles teeth of Saurornitholestes or Acheroraptor and the other is similar to teeth of Dromaeosaurus. Troodontid teeth are rare in the Fruitland and lower Kirtland formations, but are the dominant small theropod tooth in the Naashoibito assemblage. Richardoestesia is present in the Fruitland, Hunter Wash, De-na-zin, and Naashoibito members. “Paronychodon” is present in the Fruitland and lower Kirtland Formation.

The San Juan Basin contains a diverse record of small theropods. Late Campanian small theropod assemblages differ from approximately co-eval assemblages of the northern Rockies in being less diverse with only rare representatives of troodontids and a Dromaeosaurus-like taxon. The late Maashtrichtian assemblage differs in its dominance of a troodontid. These differences provide evidence for provinciality in the late Campanian and the late Maastrichtian of western North America. As in northern latest Cretaceous faunas, there is no indication for a drop in the diversity of small-bodied theropods during the Maastrichtian in New Mexico.