Inferring locomotor behavior in Paleogene mammals via eigenshape analysis

The inference of locomotor mode in Paleogene mammalian faunas has been traditionally based on qualitative comparisons between fossil postcranial skeletal elements and those of modern forms whose range of locomotor behavior is known. Recently, it has been shown that detailed functional interpretations can also be obtained using a series of geometric indices to assess shape correspondences between Oligocene carnivores and a predominantly carnivorous assemblage of modern mammalian species. This morphometric approach is generalized and extended by focusing on an analysis of ungual phalanx and proximal radial head outlines via the eigenshape technique. Results of ungual phalanx analyses show that geometric consideration of the lateral outline is sufficient to discriminate among modern arboreal/scansorial, fossorial, and cursorial species. The results also show that when modern mammalian taxa are grouped by geometric correspondences among ungual phalanx and proximal radial head outlines, the consequent associations of taxa are invariably polyphyletic, indicating widespread evolutionary convergence on a relatively small number of characteristic shapes. -from Authors