Controls on Shell Shape in Acanthoceratid Ammonites from the Cenomanian-Turonian Western Interior Seaway

Abstract

Epeiric seas have often played host to the rapid evolutionary radiations of ammonoid groups. The Cretaceous Western Interior Seaway was no exception. Members of the ornamented ammonite family Acanthoceratidae migrated into and radiated within the newly formed Western Interior Seaway during the Cenomanian. Due to the intensive work on constructing a high-resolution stratigraphic framework for the Western Interior (see Kauffman, 1986; Kauffman et al. , 1987, 1993; Kauffman and Caldwell, 1993 for overviews), this radiation of ammonites is extremely well-constrained stratigraphically, geographically, and temporally. The well-defined and limited nature of the acanthoceratid diversification makes the event a natural experiment for exploring patterns and processes associated with rapid endemic radiations.