Paleobiological Perspectives on Mesonychia, Archaeoceti, and the Origin of Whales

New specimens of middle Eocene Basilosaurus isis from Egypt include the first functional pelvic limb and foot bones known in Cetacea. These are important in corroborating the intermediate evolutionary position of archaeocetes between generalized Paleocene land mammals that used hind limbs in locomotion and Oligocene-to- Recent whales that lack functional pelvic limbs. The foot is paraxonic, consistent with derivation from mesonychid Condylarthra. Hind limbs of Basilosaurus are interpreted as copulatory guides.