Vertebral Variation and Identification of Eastern North American Pitvipers (Viperidae, Crotalinae) Using Geometric Morphometrics

Jessee, Lance D. 
jesseel@etsu.edu

 

Gause, Austin R.J.                                                                                                                                        

Schubert, Blaine W.
Department of Geosciences and                                                                                                                                

Center of Excellence in Paleontology                                                                                                                         East Tennessee State University                                                                                                                     Johnson City, Tennessee, USA


Within Pleistocene cave deposits, snake fossils tend to be relatively common and generally occur as disarticulated vertebrae. However, identification of vertebrae is often hindered by significant intra- and interspecific morphological variation along the precloacal vertebral column, a subject that has largely been neglected in fossil snake identifications. Such identifications are typically based on mid-trunk vertebrae, comparison to disarticulated modern specimens, and an over reliance on modern distributions. This study examines vertebral variation and the utility of specific viperid vertebrae in making identifications. We use 2-D geometric morphometrics to examine vertebral variation along the precloacal vertebral column of Crotalus horridus and Agkistrodon contortrix, two crotalines that are sympatric in much of the eastern United States and have similar vertebral morphologies. The focus here is to examine morphological regionalization patterns of the precloacal vertebral column. One individual of each species was chosen and every third vertebra was analyzed in anterior view using geometric morphometrics, and relative warp analyses were computed. The relative warp analyses show continual variation with mid-trunk vertebrae showing less variation than anterior and posterior trunk vertebrae. Both species show the same trends in columnar variation and that mid-trunk vertebrae can be distinguished from other vertebrae. Our next step in this study is to perform discriminant function analysis on mid-trunk vertebrae in an attempt to distinguish the two taxa. Further, we plan to incorporate other members of these genera into our analyses to assess specific and generic classifications. If this is successful, we will implement our methods on fossil specimens from Pleistocene cave sites to better understand the distribution of these snakes through time. This study also demonstrates the need for more modern snake skeletons in collections and that efforts should be made to preserve the vertebral order of those specimens.
 

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