Proceedings of the South Dakota Academy of Science,Vol. 81 (2002) 283

LATE CRETACEOUS DINOSAURS, BIG BEND NATIONAL PARK, TEXAS

Julia T. Sankey Department of Geology and Geography Vassar College Poughkeepsie, NY 12604

ABSTRACT

Dinosaurs are not as well known from southern North America compared to more northern areas such as Alberta. Big Bend National Park, Texas has one of the southernmost terrestrial records for the Late Cretaceous in North America. Work in Big Bend provides an important and new geographic per- spective on dinosaur diversity during the final ten million years of the Creta- ceous from southern North America, leading up to the mass extinctions at the Cretaceous/Tertiary (K/T) boundary. Dinosaur teeth were collected from mi- crofossil sites from the Late Cretaceous upper Aguja and lower Tornillo forma- tions, spanning the late Campanian to late Maastrichtian (~74 to 67 Ma). In ad- dition to detailed descriptions and illustrations of the dinosaur teeth, measure- ments and bivariate plots quantify their variation, allowing comparison with well-studied collections from similar-aged deposits. Taxa include herbivorous dinosaurs: pachycephalosaurid (dome-head), ceratopsid (horned), ankylosaur (armored), hadrosaurid (duck-billed) and carnivorous dinosaurs: tyran- nosaurid, Saurornitholestes cf. S. langstoni, Saurornitholestes sp., Richar- doestesia cf. R. gilmorei, R. isosceles, and "Paronychodon". Most taxa are rep- resented by teeth from hatchlings or juveniles, demonstrating that these di- nosaurs nested in the area. "Paronychodon" and Saurornitholestes sp. are rare and occur only in the Tornillo Formation, initial evidence that the Maastrichtian and Campanian theropod faunas in Big Bend were distinct, a similar pattern in northern assemblages. Absent from both the Campanian and Maastrichtian in Big Bend are Dromaeosaurus and Troodon, common in northern areas. More research is needed to confirm this pattern and to better document the dinosaur diversity in the Big Bend area.