Whales are extraordinary creatures which are said to be evolved from land beasts 50 million years ago. Even today some whales still have a tiny leg or two attached to their enormous bodies, a reminder of what they once were. Some people, however, reject the following ideas that may link whales to these beasts of long ago.
Oddly enough, the whale's ancestors did the reverse of how they got there in the first place. Millions of years ago, the first animals crawled from the sea to the land. We know that all this is true because of Phil Gingerich, a paleontologist who discovered a 52-million-year-old skull in Pakistan in 1978. The fossils resembled those of Creodonts, which are wolf-sized carnivores that lived between 60 and 37 million years ago, in the early Eocene epoch (part of the Tertiary Period in the Cenozoic Era, and lasted from about 54.8 to 33.7 million years ago). But the skull, called Pakicetus, also had characteristics in common with the Archaeocetes, the oldest known whales. The ear region, for example, was in the middle of evolving from a terrestrial to an aquatic mammal's.
Another set of fossils, called Ambulocetus, was an amphibious animal whose front legs had small fingers and were hoofed, while the hind legs were adapted for swimming. This let the creature travel in both land and water.
Next we have the Rhodocetus who had all the fixings to live in the water. Its neck and vertebrae were shorter and more stable, like that of many marine mammals today. The ear was even more specialized for hearing under the water, and lastly, its legs were disengaged from the pelvis.
During the age of dinosaurs 40 million years ago, the Basilosaurus lurked in the waters with its long, flexible body and giant flippers. Though it could not walk on land, fossils show that the Basilosaurus still had tiny legs attached to his body, much like a portion of the whales of today.
Lastly, the Dorudon came out to play. It was a contemporary of Basilosaurus in the late Eocene period (about 40 million years ago) and probably represents the group most likely to be ancestral to modern whales. This mammal's vertebrae were much shorter than that of the Basilosaurus.
Though none of the previously mentioned mammals have been categorized as direct ancestors of the whales we see today, scientific evidence does indeed suggest so. Now whales are seen as long, thick creatures, with horizontal flukes that are a signature for them, along with their shorter vertebrae. Perhaps occasionally, if given an up close and personal look, you just might see one with stubby little legs. Then you will be stuck to wonder the origins of this magnificent creature.
Sutera, Ray. "The Origin of Whales and the Power of Independent Evidence". The TalkOrigins Archive. http://www.talkorigins.org/features/whales/. Copyright 2001
[posted: August 10, 2001]. Originally printed in The National Center for Science Education. 4/6/07.