Basilosaurus Giant Prehistoric Basilosaurus, early whale tooth molar, Replica 3983 cast replica

Basilosaurus (meaning "king lizard") is a genus of large, predatory, prehistoric whale (mammal) from the late Eocene. It is one of the largest animals known to exist between the K–Pg extinction event when modern cetaceans began to reach enormous sizes. B. cetoides measured 17–20 metres (56–66 ft) long and weighed more than 6.4 tons, while B. isis measured 15–18 metres (49–59 ft) long and weighed nearly 7.2 tons. Basilosaurus looked vastly different from all modern whales and dolphins. It had an extremely long, slender body, and had a narrow snout lined with teeth of different shapes. It had large canine teeth and molars that were vastly different that any living whale. The head of Basilosaurus did not have room for a melon like modern toothed whales, and the brain was smaller in comparison, as well. They are not believed to have had the social capabilities of modern whales.