Morphometric analysis of carapacial bones: discriminating between two genera of South Texas (North America) Pleistocene tortoises (Testudinidae)

Abstract

Several species of large Pleistocene tortoises (genera Hesperotestudo and Gopherus) occurred in the southern region of the United States (Texas) and fragmentary skeletal remains are commonly encountered. In some cases, fossil tortoises can be identified using single carapace or plastron bones, however, there can be ambiguity when identifying to species level. Additionally, non-mature specimens may be problematic to differentiate. To further quantify the identification of two genera of large Pleistocene tortoises, nuchal and neural bones (n = 58) from the collection sites in South Texas were examined and measured. Scatter plots, based on length, width and thickness measurements and ratios were developed for both nuchal and neural elements. The analysis supports the ability to differentiate between large species of late Pleistocene tortoises (Hesperotestudo and Gopherus) from South Texas based not only on diagnostic descriptions but also by different suites of measurements. These measurements and ratios may also be useful for identification and separation of additional genera/species of tortoises throughout North America, both extinct and extant.