Catastrophic Events Conference 3148.pdf

LATE THEROPOD DIVERSITY: LATITUDINAL DIFFERENCES IN NORTH AMERICA AND IMPLICATIONS FOR THE K/T EXTINCTIONS. J.T. Sankey, Museum of Geology, South Dakota School of Mines and Technology, 501 E. Saint Joseph Ave., Rapid City, SD, 57701, U.S.A. [email protected]

Although the evidence for an impact at the end of the collecting. from Alberta are in the Royal Tyrrell Cretaceous no longer makes this event controversial, the Museum of Paleontology (Drumheller, Alberta) and link between an impact and the terrestrial those from Big Bend, at Louisiana State University extinctions is still controversial among some (Baton Rouge) and University of Texas at Austin. There paleontologists. The proposed ecosystem collapse as a are only five theropods from Big Bend: result of impact does not fit with the selective nature for , cf. R. gilmorei, these extinctions. This paper reports on the differences Richardoestesia sp. nov., Paronychodon lacustris, and in theropod dinosaur diversity between southern and tyrannosaurid [2, 3, 4]. However, there are at more taxa northern North America during the last 10 million years from Albertan deposits, including , of the Cretaceous, and suggests that climatic and , "", and several environmental changes were important factors in the tyrannosaurids [5, 6, 7]. dinosaur extinctions. Paleoecologically, the Aguja and Javelina (late Temperature and rainfall differences along a north- to latest ) of Big Bend may south latitudinal gradient in the Western Interior of North have been more similar to the lower America resulted in distinct terrestrial faunal and floral (latest Maastrichtian) of Alberta: both had warm, dry, provinces during the late Campanian. The open environments producing lower theropod diversity "" dinosaur fauna was from Wyoming to and abundance. This connection between climate, the north and the "Kritosaurus" fauna occurred to the environment, and theropod diversity suggests that these south. These faunas correspond approximately to the factors were important in their extinctions. Aquillapollenites and Normapolles palynofloral provinces. More temperate and humid climates, with References more closed-canopy forests occurred to the north and warm, dry, and non-seasonal climates, with more open- [1] Lehman T.M. (1997) Dinofest Intl, Phila. Acad. Nat. canopy woodlands occurred to the south [1]. Sci., 223-240. [2] Standhardt B. R. (1986) Ph.D. Diss., southern theropods are not as well Louisiana State Univ., 1-298. [3] Rowe T. et al. (1992) J. known, especially from west Texas (Aguja and Javelina Vert. Paleo, 12, 472-493. [4] Sankey J.T. (1998) Ph.D. Formations, Big Bend National Park), where deposits Diss., Louisiana State Univ, 1-263. [5] Currie P. J. et al. have received less attention, have less outcrop area, and (1990) in Dinosaur Systematics: Perspectives and are generally less -rich. Northern Late Cretaceous Approaches (eds, Carpenter, K. & Currie, P.J.) 107-125 theropods are better known, especially from Alberta (Cambridge Univ. Press). [6] Baszio, S. (1997b) Courier (Judith River and Edmonton Groups), due to more Forschungsinstitut Senckenberg, 196, 33-77. [7] Sankey, intense collection, more outcrop area, and richer J.T. et al. (in prep). [8] Baszio, S. (1997a) Courier deposits. Forschungsinstitut Senckenberg, 196, 1-31. Fossils studied are teeth collected by various workers by screening microvertebrate sites and by surface