Wiktionary
n. Any of several very large extinct cetaceans, of the family ''(taxlink Basilosauridae family noshow=1)'', from the late Eocene
Wikipedia
Basilosaurus ("king lizard") is a genus of early whales that lived in the late Eocene. 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 wished to rename the creature Zeuglodon ("yoked tooth"), but, per taxonomic rules, the creature's first name remained permanent. Fossils of B. isis have been found in Egypt and Jordan.
The species B. cetoides is the state fossil of Mississippi and Alabama.
Usage examples of "basilosaurus".
The Alabama doctors declared it a huge reptile, and bestowed upon it the name of Basilosaurus.
So in the mid-Eocene we find the earliest fossils of whales, such as the sixty-foot (20 m) long Basilosaurus, which had a pair of tiny legs at the base of its long tail.
Only a few years earlier, his friend Georg Schweinfurth had announced the discovery of a new whale species (Zeuglodon osiris—now called Basilosaurus) from the rocks of the Fayoum.