Longest basilosaurid

Basilosaurids were unusual prehistoric whales that existed during the late mid- to early-late Eocene epoch, approximately 40–34 million years ago. Most of them were characterised by extremely lengthy, serpentine or eel-like bodies, and some grew to immense sizes. The longest basilosaurid species presently known from the fossil record is Basilosaurus cetoides, which attained a total length of up to 18 m (and possibly more). Its great length was due to marked elongation of the central portion (centrum) of each of the thoracic and the anterior caudal vertebrae in its backbone.

The genus name Basilosaurus translates as "king lizard", which seems an odd name to give a mammal (as whales are), but is the result of an infamous case of zoological misidentification. The first fossil specimen of this prehistoric whale brought to scientific attention and only consisting of partial remains had been unearthed in the USA and was examined by American palaeontologist Richard Harlan. Unfortunately, he erroneously assumed that it was some kind of great sea reptile, so when he formally described it in 1847 he named it Basilosaurus. His British counterpart, Prof. Sir Richard Owen, conversely, recognized that it was actually a mammal, and renamed it Zeuglodon, but according to the laws of scientific nomenclature the first scientific name given to a species takes precedence, so its genus remains Basilosaurus, but "zeuglodont" is popularly used as a common name for it.