EVOLUTION, DISPERSAL, AND HABITAT PREFERENCE OF BASILOSAURUS (MAMMALIA: CETACEA) IN THE SOUTHEASTERN UNITED STATES: NEW EVIDENCE FROM THE EOCENE OF SOUTHWEST GEORGIA

Archaeocetes are primitive cetaceans that originated during the early Eocene in Indo-Pakistan. By the end of the Eocene, archaeocetes were distributed worldwide. Semiaquatic protocetid archaeocetes were the first to reach North America during the early middle Eocene, followed by fully aquatic basilosaurids in the late Eocene. The archaeocete Basilosaurus reached lengths of up to 70 feet and is characterized by elongated posterior thoracic, lumbar, and anterior caudal vertebrae. Basilosaurus isis is known from Egypt and Jordan, whereas Basilosaurus cetoides is known principally from North America. The two taxa are distinguished mainly by the slightly larger size of B. cetoides. Most occurrences of Basilosaurus in North America are within the Gulf Coastal Plain. Fewer specimens have been found in the Atlantic Coastal Plain. In Georgia, there are only three confirmed reports of Basilosaurus, two of which are of skeletal fragments. Here we report a new specimen of Basilosaurus found on the banks of the Flint River in Albany, Georgia. This specimen appears to be the most complete Basilosaurus known from Georgia, consisting of a series of elongated vertebrae and some probable rib fragments. Upon initial discovery, the specimen included five nearly complete vertebrae and fragments of two more, but three vertebrae have since been stolen. The excavation is ongoing, and there is potential for recovery of additional material beyond what is currently excavated. The fossil is encased in the Ocala Limestone, a fine-grained, white to cream colored limestone that formed during the late Eocene (Priabonian: 37.2-33.9 Ma) in the shallow open waters of the continental shelf. The distribution of Basilosaurus in North America is limited to marine deposits, but it is unclear why the taxon is abundantly known in Mississippi and Alabama and underrepresented in neighboring Georgia. Here we investigate the facies, temporal, and geographic distribution of Basilosaurus in North America in order to identify paleoenvironmental and geographic limitations to its distribution. Elucidation of these patterns will ultimately provide a better understanding of the timing of dispersal and habitat preference of Basilosaurus, with important implications for the evolution of archaeocetes in southeastern North America.