| When did it live? | Eocene Epoch (Priabonian Stage; 37.8 to 33.9 million years ago) |
| Where was the fossil found? | Fayum Province, Egypt |
| Who are its relatives? | Whales |
| A little known fact | Basilosaurus means ‘king lizard' |
Basilosaurus isis was an enormous aquatic predator that lived during the Eocene Period, approximately 35 million years ago. With a name meaning 'king lizard,' Basilosaurus was misidentified by early researchers as a sea-going reptile. Only later did scientists conclude this creature is an early relative of today’s whales, a successful group of marine mammals. Basilosaurus isis offers an important look into how whales eventually lost their back legs and mastered their current underwater habitat.
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Basilosaurus was an impressively large (15-18 meters in length) whale with a long, snake or eel-like body. It belonged to a group of early whales collectively called archaeocetes, which means ‘ancient whales.’ It is thought Basilosaurus moved through the water with an undulatory, or wave-like, motion: using its tail to propel, its forelimbs as flippers to steer, and its heavy ribs to stabilize as it swam.
Its skull was primitive compared to a modern whale, with a small brain. But what Basilosaurus lacked in brain, it made up for in bite. Basilosaurus had large, blade-like cheek teeth that each bore numerous cusps. These teeth, which provided a clue to early paleontologists that Basilosaurus was a mammal, allowed this early whale to shear, crush, and puncture its food. And the geometry of the skull suggests the bite force of Basilosaurus was substantial. Add these things together and Basilosaurus was likely the apex (or top) predator of its ecosystem. It feasted on bony fishes, sharks, sea cows, turtles, and even other species of whales! How do we know? Some fossils of Basilosaurus have been found with the remains of their last meals still inside, while bones of their unfortunate victims bear the tell-tale signs of the teeth of this fearsome predator.
So, what about the hind legs mentioned at the beginning? Basilosaurus did have hind legs, much like land-dwelling mammals and other early whales—but they were tiny. With a body longer than a schoolbus, Basilosaurus had hind legs shorter than the arms of a person! Furthermore, its hind limbs and hips were not attached to its backbone. Legs like this couldn’t bear weight and so weren’t used in walking, but they were clearly functional. With moveable joints and the ability to rotate, it is hypothesized Basilosaurus used their hindlimbs as guides during mating.
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The information presented in this module comes from William Sanders, UMMP Chief Vertebrate Preparator and Associate Research Scientist. Read the full article here
