By 40 million years ago, Basilosaurus -- clearly an animal fully adapted to an aquatic environment -- was swimming the ancient seas, propelled by its sturdy flippers and long, flexible body.

Did the Basilosaurus have legs?

New specimens of middle Eocene Basilosaurus isis from Egypt include the first functional pelvic limb and foot bones known in Cetacea. ... The foot is paraxonic, consistent with derivation from mesonychid Condylarthra. Hind limbs of Basilosaurus are interpreted as copulatory guides.

Why did the Basilosaurus evolve?

Basilosaurus shows the link or intermediate between whales and their terrestrial ungulate ancestors. The theory is that some land-living ungulates favoured munching on plants at the water's edge which had the added advantage of allowing them to easily hide from danger in shallow water.