Basilosaurus ('king lizard') was a genus of primitive, predatory whales, the first of its kind discovered. When its fossils were first discovered, it was originally believed to be a giant lizard. It reached lengths of 15-20 metres (49-66 ft) and fed on large fish and sharks. Like extant whales, it still has hind limbs from its land-dwelling ancestors, though they lie outside the body and can only be moved a little, rendering them useless for helping to propel its body. In the southern United States, during the early 19th century, Basilosaurus skeletons were so common they were often used as furniture. The famous image of a giant skeleton in the sand is of a Basilosaurus.

(Eocene, 41.3-33.9 million years ago)