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