A Diagnosis of Alligator mississippiensis Bite Marks with Comparisons to Existing Crocodylian Datasets

Abstract

Crocodylians are known to consume and modify bones, but actualistic observations of their bite marks have been limited to forensic case studies and surveys of two taxa: Crocodylus niloticus and Crocodylus porosus. To further explore patterns of crocodylian bite mark expression, we conducted a survey of traces left by Alligator mississippiensis. We compared the results to pre-existing crocodylian datasets regarding the potentially diagnostic traits of bisected marks, hook scores, and a lack of furrows. Mark type did not correlate with vital statistics of the sampled animals or collections protocol. Bisected marks were found in rates similar to those seen in one previous survey of C. niloticus, and rates of hook scoring and bone breakage were higher. These traces were all present in higher rates than those reported in C. porosus. Unlike results seen in Crocodylus, furrows were identified in the A. mississippiensis samples. Hook scores were also identified, but recent surveys of non-crocodylian taxa have shown that these features are not unique to crocodylians and instead are related to inertial feeding strategies. The presence and rate of bisected marks found in this study bolster the interpretation that these traces are a clade-wide phenomenon and a useful diagnostic indicator for Crocodylia.

Keywords:

• Tooth mark
• Feeding trace
• Trophic interaction
• Crocodylia

ACKNOWLEDGMENTS

The Saint Augustine Alligator Farm and curator of reptiles David Kledzik provided access to animals. Southeastern Provisional and Swaggerty's Farms provided the cow and pig samples. The Iowa Department of the State Archaeologist, the McClung Museum of Natural History and Culture, and Fred and Janet Drumheller provided storage space and equipment for sample processing and imaging. The University of Iowa Central Microscopy Research Laboratories provided training and access to scanning electron microscopes. This study represents part of a dissertation completed in partial fulfillment of a PhD at the University of Iowa. Committee members included Nancy Budd, Jim Enloe, Jonathan Adrain, Hallie Sims, and Walter Klippel. The following people also provided helpful discussion, feedback, and encouragement: Michelle Stocker, Colin Sumrall, Linda Kah, Troy Fadiga, Julia McHugh, Talia Karim, Jake Horton, Dorothy May, and the UI Paleontological Discussion Group.

FUNDING

Support for this study was provided though NSF DEB 0444133 and DEB 1257786-125748 to C. A. B. and the University of Iowa Department of Geosciences Littlefield Family Fund.