STATISTICAL CLUSTERING ANALYSIS OF POSTCRANIAL MORPHOLOGY

Vertebrate paleontology often concentrates on craniodental material (teeth and skulls), but postcranial material can be much more common in any assemblage that underwent significant transport and often represents the only evidence of taxonomic membership. Yet standard morphological comparisons miss subtle differences in size and shape of postcranial material of functionally constrained bones. Previous work demonstrates that statistical analysis of 2-D and 3-D morphometrics can be used to differentiate taxa, but shape-differences arise from more than just species or genus level differences. In this study, we examine statistical distributions of linear measurements of postcranial structure to identify how the shapes of these structures cluster or diverge in closely related species and within sexually dimorphic species. The order Artiodactyla includes families such as the camels, where the size and shape of postcranial structures reliably differentiate species and families where sexual dimorphism is more important, such as deer. We use measurements of the astragali, as this durable ankle bone is common enough in the Cenozoic fossil record and to be compared in detail with modern assemblages. . A Principal Component Analysis of eight standardized measurements on the astragali reveals clustering of these morphological proxies at a family level, allowing us to classify these taxa. Multivariate analysis of variance, can distinguish male and female deer of the same family, but we see no show significant sex differences in pronghorn antelope. Finally, the interspecific and intraspecific differences observed in modern artiodactyls served as a comparison to the fossil group the Palaeomerycidae. This family has been variably suggested to be related to deer, camels, or giraffes. Palaeomerycidae astragali exhibit statistical clustering more similar to camels than deer or pronghorn, and previously unrecognized sexual dimorphism.