Exploring late Cretaceous western interior ammonoid geographic range and its relationship to diversity dynamics using geographic information systems (GIS)

by III. MacKenzie, Richard Allen

Margaret M. Yacobucci, Advisor Questions related to the ecology, evolution, and extinction of ammonoids require quantitative paleobiogeographic data to be answered, but in the past these data have been difficult to compile, visualize, quantify and interpret. Geographic Information Systems (GIS) has been used recently to expand the knowledge of the geosciences, but has been underutilized in the addressing of paleontologic questions. A geographic database of individual Upper Cretaceous fossil ammonoid data from the Western Interior of North America was collected from several sources including publications, field work, and museum collections using Microsoft Excel as the storage medium. The use of this program offers an efficient means to store individual fossil information and allows for easy sorting, transferability, and the application of mathematic formulas. Data was collected in three major sections, including full taxonomic and fossil description, modern and paleogeographic locality data, and geotemporal data. Once the data were collected and placed in the Excel spreadsheet, they were then sorted and transferred into a Microsoft Access database for use in Geographic Information System (GIS) software. ArcMap 9.1 GIS software was then used to sort and display ammonoid biogeographic information at the suborder and superfamily taxonomic level of hierarchy. Once the ammonoid biogeographic information was displayed, polygons delineating ammonoid area were hand drawn, and the area in square kilometers calculated. The area occupied in the Western Interior by the ammonoids was then compared to total generic diversity, mean standing diversity, and origination and extinction rates. It was discovered by a simple visual line trend comparison that a positive correlation exists between the geographic range of the suborders Ancyloceratina and Ammonitina and origination iii and extinction rates from the Lower Cenomanian through the Middle Coniacian. The correlation between geographic range and evolutionary rates becomes negative from the Middle Coniacian through the Lower Maastrichtian, indicating a possible fundamental change in the way Western Interior ammonoid area and origination and extinction rates relate to each other. The different superfamilies show different relationships when comparing their Western Interior geographic range to their diversity dynamics providing evidence that each superfamily responds to changing conditions in the seaway in different ways. Another discovery was that the species in the genus Scaphites show 4 distinct habitat patterns: an east-west trending pattern, a north-south trending pattern, a small cluster pattern, and a wide spread pattern. This thesis also demonstrates new and refined methods to study paleontological questions using GIS and topographic mapping software. iv This thesis is dedicated to Richard Allen MacKenzie II and Yolande Eve Gibson, both of whom lost their battles with cancer during its completion. They are sorely missed, and the world is a dimmer place without them. v