LOCOMOTION AND BEHAVIOR OF THE ANCIENT WHALE GEORGIACETUS

Georgiacetus vogtlensis is one of the most primitive archaeocetes from North America. Discovered in the northern Atlantic Coastal Plain of Georgia in 1983, it has been interpreted as semi-aquatic, but shows important adaptions toward fully aquatic behavior, including the lack of articulation between the pelvis and sacral vertebrae. Among all protocetids, Georgiacetus is most closely related to the clade Pelagiceti, which includes the common ancestor of all fully aquatic archaeocetes and their descendants, including modern whales. The goal of this study is to elucidate aspects of Georgiacetus locomotion and behavior and investigate changes in skeletal morphology that occurred during the land-to-sea transition of whale evolution. This goal will be achieved via multivariate analyses (Discriminant Function and Canonical Variates Analyses) of 17 measurements of lumbar vertebrae from more than 30 modern and extinct mammals. Lumbar vertebrae are used because they likely underwent the most drastic changes during the early stages of whale evolution, as dorsomobile archaeocetes evolved from dorsostable artiodactyls. Discriminant Function Analysis (DFA) will first be used to classify Georgiacetus into a semi-aquatic or fully aquatic group based on comparison with modern mammals of known lifestyle. Canonical Variates Analysis (CVA) will then be used to illustrate differences in the morphology of lumbar vertebrae among modern and extinct fully aquatic, semi-aquatic, and terrestrial species, including Georgiacetus and other archaeocetes. Based on previous studies, we hypothesize that Georgiacetus will be classified as semi-aquatic using DFA. However, based on its close phylogenetic relationship with Pelagiceti, we anticipate that it will be most like the fully aquatic group than any other member of the semi-aquatic group in the CVA.