Your Daily Fossil

Basilosaurus

Mounted skeleton on display at the Smithsonian.  

When: Late Eocene (40-34 million years ago)

Where: North American and the MIddle East. 

What: Basilosaurus is an extinct whale. The word ‘saurus’, which means lizard, is in its name as the first fossils found in the early 1800s were isolated vertebra which were misidentified as reptilian. Soon thereafter additional material was found which easily diagnosed Basilosaurus as a form of whale.  However, due to the rules of nomenclature, the first name that is applied is the name of the taxon for all time. The first Basilosaurus material was found in Louisiana, USA and specimens were commonly found throughout the southern United States. At one point vertebra were turning up so often they were used as furniture by the locals. 

Basilosaurus is not closely related to any modern whales, diverging from the cetacean lineage prior to the odontocete (toothed whale) mysticete (baleen whales) spilt. Though it is not the longest whale ever known, at ‘only’ 72 feet (22 meters) long , it reached this length in a manner unlike modern cetaceans. All of this elongation comes from duplications of vertebra past the ribs whereas modern whales of this length are just overall bigger in all aspects - Basilosaurus was extremely narrow for its body length. Basilosaurus did not swim like modern whales, which move the whole tail as one unit, instead it is thought it swam much more like an eel, with the movement undulating though the long body - though in a vertical fashion rather than horizontal. Another interesting aspect of Basilosaurus is it retained extremely small hind limbs, which were useless in locomotion. These tiny appendages were most likely used as copulatory guides, such as seen in some snakes, to make sure that the proper bits of a mating pair lined up.