bas·i·lo·sau·rus / ˌbasələˈsôrəs/ • n. (pl. -sau·rus·es or -sau·ri / -ˈsôrī/ ) a large marine cetacean (Basilosaurus isis) of the Eocene epoch, having a long, slender body and vestigial fore and hind limbs. Fossils were discovered in the early 1990s.

Basilosaurus (order Cetacea, suborder Archaeoceti) One of the best-known archaeocetes; it grew to approximately 20 m in length and lived during the Upper Eocene. It was discovered recently that Basilosaurus retained small hind limbs, useless for locomotion, but perhaps usable as claspers during copulation.

Basilosaurus (order Cetacea, suborder Archaeoceti) One of the best-known archaeocetes; it grew to approximately 20 m in length and lived during the Upper Eocene. It was discovered recently that Basilosaurus retained small hind limbs, useless for locomotion, but perhaps usable as claspers during copulation.