Name: Basilosaurus (King lizard). Phonetic: Ba-sil-oh-sore-us. Named By: Richard Harlan - 1847. Synonyms: Zeuglodon. Classification: Chordata, Mammalia, Cetacea, Archaeoceti, Basilosauridae. Species: B. cetoides (type), B. drazindai, B. harwoodi, B. isis, B. caucasicus, B. paulsoni, B. puschi, B. vredensis, B. wanklyni. Type: Carnivore. Size: Average 18 meters long. Known locations: USA. Egypt, Wadi Al-Hitan. Pakistan. Time period: Bartonian to Priabonian of the Eocene. Fossil representation: Lots of known specimens.
The one thing about Basilosaurus that instantly causes confusion is its name. When first studied and named by Richard Harlan, he came to the conclusion that it was most likely a marine reptile, and so named it Basilosaurus, or ‘King lizard’. It was not until the remains were studied by Sir Richard Owen that they were confirmed as mammalian. Owen then proposed that Basilosaurus should be renamed Zeuglodon (Yoke teeth), but because Basilosaurus was the officially registered name, it could not be changed, so Zeuglodon became a synonym instead of a replacement. Basilosaurus represents one of the earliest whales although its actually descended from terrestrial mammals like Ambulocetus. Evidence for this can be seen in the flippers. The front flippers still have an elbow joint, something that today is only seen in seals. The back flippers where the hind legs would have been in its ancestor are greatly reduced and although they may have been used to get extra grip on a mate, they would eventually disappear in later whales. The size of its flippers in comparison with the massive bulk of its body means that it was almost certainly an entirely pelagic animal. The large jaws of Basilosaurus housed teeth suitable for catching prey that would not have been especially small, perhaps smaller whales or large fish that while smaller than Basilosaurus, but were still too large for most other predators to tackle. Superficially the fossils of Basilosaurus skulls resemble the skulls of mosasaurs that swam the oceans tens of millions of years earlier, disappearing from the fossil record at the time of the KT extinction 65 million years ago. It is partly for this reason that Basilosaurus was misidentified as a reptile because mosasaur remains were known, yet no one was aware that the early whales looked so similar. The skull also has a reduced area for the brain when compared to modern whales. Going on the basis that larger brained cetaceans are typically more social, Basilosaurus itself may have been a solitary predator. Although not preserved, the structure of the tail vertebrae suggests support for a tail fluke as seen in modern cetaceans. The reduced limbs would probably have been of little use in actual locomotion leading to the suggestion that Basilosaurus used an undulating motion to propel itself in the water. This up and down motion may have also provided quick bursts of speed at prey items.