Basilosaurus

Basilosaurus isis had a stretched-out body that reached up to 15 meters in length. The lumbar and caudal vertebrae were extremely elongated. The animal swam by means of undulating up- and downward motions of its body. Unlike modern whales, this prehistoric marine mammal, which lived more than 35 million years ago, still possessed posterior extremities. This offers proof that whales descended from land-dwelling four-legged animals. The dentition, which does not consist of the uniformly pointed teeth of modern whales, also shows similarities to the teeth of terrestrial predators.