Basilosaurus

Basilosaurus is a genus of cetacean that lived from 40 to 34 million years ago in the Late Eocene. The first "Basilosaurus" fossils were found in Louisiana, USA, but another species was soon discovered preserved in large numbers in the Fayum deposits of Egypt.
The first fossil of "B. cetoides" was discovered in the United States and was initially believed to be some sort of reptile, hence the suffix -"saurus", but it was later found to be a marine mammal. Richard Owen wanted to rename the creature Zeuglodon ("yoked tooth"), but by taxonomic rules the creature's first name remained permanent. Fossils of "B. isis" have been found in Egypt and Jordan. 
Far from being a marine reptile, "Basilosaurus" is a stage in the evolution of whales. At 15–20 m (49–66 ft), "Basilosaurus" was one of the largest oceanic animals of its time. Basilosaurus went extinct during the Eocene Extinction.