ECOLOGY OF THE AMMONITE SUPERFAMILY ACANTHOCERATOIDEA FROM THE CENOMANIAN-TURONIAN WESTERN INTERIOR SEAWAY USING WESTERMANN MORPHOSPACE
Shell measurements from 225 acanthoceratoid specimens from the Middle Cenomanian through the Upper Turonian, including shell diameter, whorl heights, whorl breadth, and umbilical diameter, were made. Shape ratios were calculated and normalized, then used to produce ternary diagrams representing Westermann morphospace. Acanthoceratidae, the most diverse of the acanthoceratoid families, shows much higher morphological disparity than other families, occupying much of the central region of the morphospace. Other families, all descendants of Acanthoceratidae, segregate into one or another peripheral region of the morphospace. For example, coilopoceratid specimens fall in the nektonic region while collignoniceratid specimens fall towards the demersal-planktonic region. The high morphological disparity of Acanthoceratidae is consistent with previous work showing the plasticity and variability in the group. The distributions of the descendant families support the claim that each family was derived from a different taxonomic, morphologic, and ecological precursor within Acanthoceratidae. Future work will investigate phylogenetic relationships within Acanthoceratoidea to better clarify these evolutionary transitions.