Paper No. 6
Presentation Time: 9:15 AM

A SEA WITHOUT SNAILS: WHY ARE GASTROPODS LESS DIVERSE AND ABUNDANT IN THE CRETACEOUS WESTERN INTERIOR SEAWAY?


FRIEND, Dana S., Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY 14850, ALLMON, Warren D., Paleontological Research Institution, 1259 Trumansburg Road, Ithaca, NY 14850, HARRIES, Peter J., Department of Geology, University of South Florida, 4202 E. Fowler Ave., NES107, Tampa, FL 33620, MYERS, Corinne, Geology, University of Kansas, 1475 Jayhawk Blvd, 120 Lindley Hall, Lawrence, KS 66045, GEARY, Dana H., Dept. of Geoscience, Univ of Wisconsin-Madison, 1215 W. Dayton St, Madison, WI 53706 and MACKENZIE III, Richard A., Department of Geological Sciences, University of Florida, 241 Williamson Hall, PO Box 112120, Gainesville, FL 32611, wda1@cornell.edu

Large, low-latitude (i.e., warm) epicratonic seas are largely absent in the modern world. In this sense, such seas are “non-uniformitarian” or “non­­analog” environments, and are therefore generally more difficult to study than environments with closer modern equivalents. The large, epicratonic sea known as the Western Interior Seaway (WIS) intermittently covered much of the central-western portion of North America, from the Gulf of Mexico to the Arctic, during much of the Late Cretaceous (Cenomanian-Maastrichtian), and was home to diverse and abundant marine invertebrate faunas. Gastropods, however, seem to show comparatively lower diversity and abundance in the Late Cretaceous WIS than in similar-aged assemblages elsewhere (e.g., Gulf and Atlantic coastal plains, Pacific coast, Europe). We have begun to investigate this pattern by compiling a new set of collections-based data on gastropod diversity and abundance, assembled from the Paleobiology Database, published and unpublished faunal lists, examination of museum collections, and new field collections.

Our preliminary diversity data (number of genera) pooled by state confirm previous results of Sohl (1969, 1987), which showed a typical latitudinal diversity gradient for gastropods by “province” within the WIS, similar to those on the Atlantic coastal plain and Pacific coast: higher number of genera in the southern part of the WIS, and lower to the north. Our data, however, also allow us to examine within-collection (“alpha”) gastropod diversity, which shows no latitudinal pattern within the WIS, but does show a significantly lower mean value in the WIS (1.2 genera) compared to the Pacific and Atlantic coasts (2.1 genera). Our preliminary abundance data (number of specimens per collection) also show no clear latitudinal pattern, but do show a significantly lower mean value in the WIS (18.8) compared to the Pacific and Atlantic coasts (58.3). Explanations for these patterns remain unclear and incompletely explored, but may be related to the distinctive (non-analog) environmental conditions present in the Late Cretaceous WIS.