Basilosaurus is an extinct genus of highly predatory archaic whale, or ancient whale, that lived during the Eocene epoch of North America and Eurasia. It belonged to the family of basilosaurs, containing the first fully aquatic cetaceans. Basilosaurus was very large and could grow up to 20 meters in length and weighted up to 60.000 kg! It mouth was filled with large teeth and it probably hunted large animals, like other cetaceans, fish and marine reptiles. It still retained its hind limbs, but they were probably vestigial, although some believe that they still had a purpose during mating, using them to hold on to its partner.
North America, Africa and Asia
The genus of Basilosaurus consists of two species of which B. cetoides lived in North America during the Eocene epoch. When first discovered, scientists believed that Basilosaurus was a marine reptile and therefore gave its name, meaning "king lizard". Further investigation into the fossils showed that its bones weren't made for deep dives due to their hollow inside. This means that it probably hunted only in the top layer near the surface. It wasn't a fast swimmer either or at least not for a long time. It therefore probably hunted by surprising its prey from below.