Meeting Abstract

P2-109   -   Quantifying Shell Patterning Helps Identify Species of Softshell Turtles Pamfilie, AM*; Espinal, MD; Vitek, NS; Stony Brook University; Stony Brook University; Stony Brook University alexandra.pamfilie@stonybrook.edu

Soft-shelled turtles (Trionychidae) display characteristic pits and ridges, or “sculpturing”, on the bony carapace. Variation in the pattern of sculpturing may be useful in classifying fossilized shell fragments. However, while past attempts were able to discern qualitative differences in certain best-case scenarios, most early uses of sculpturing traits have been reevaluated as unreliable in the face of intraspecific variation. The potential of sculpturing to contain consistently reliable, quantitative, taxonomically informative traits remains underexplored. Here, we revisit this idea by quantifying trionychid shell patterning with topographic measurement techniques more commonly applied to nonhomologous quantification of mammalian teeth. We assess potential sources of variation and accuracy of these metrics for species identification. Carapaces of extant specimens used in this study included members of the species Apalone ferox, Apalone spinifera, and Amyda cartilaginea and were obtained from the herpetology collections of the Florida Museum of Natural History. 3D scans of shells were systematically sampled to create digital “fragments” of consistent size, known identity and known position on the carapace. The external surface of each fragment was quantified using three topographic measurements from the molaR package in RStudio: the Dirichlet Normal Energy (DNE), Relief Index (RFI), and Occlusal Patch Count Rotated (OPCR). Results suggest there is measurable and differing variation at the species, individual, and carapace location levels of analysis. Additionally, linear discriminant analysis (LDA) correctly predicts a sample’s species identity from DNE, RFI, and OPCR approximately 74% of the time. These measures may provide a method for identifying shell fragments that are currently identifiable only as Trionychidae indet.