Marine Biology

Evolutionwhale Evolution Mammalsleviathans

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Acceptable scientific theory has determined that life began in the oceans and, through millions of years of evolutionary transitions, sea creatures began to develop limbs instead of fins and flippers, and crawled out of the oceans to become the first land-dwellers.

One might logically conclude that whales must have evolved from some type of fish, yet they are warm-blooded, air-breathing mammals, giving birth to live offspring, and possessing large brains. The only thing they really have in common with fish is that they live in the oceans.

In 1883, William Flower, a Victorian scientist, introduced the theory that whales evolved from a group of hoofed mammals known as ungulates. His hypothesis seemed ridiculous at the time. How could dolphins, humpbacks and Orcas have ancestors that were more closely related to pigs, horses, and cows than to marine life?

Zoologists are no longer scoffing at Flower's idea. Over the last three decades, fossil evidence has been discovered suggesting that the whale's evolution is the complete opposite of traditional theory. It seems that the whale's ancestors were actually land-dwellers first, and then returned to the seas. Instead of developing limbs from fins and flippers, whales developed flippers and fins from what used to be limbs, hoofed limbs.

One major turning point occurred in Pakistan, in 1978, when paleontologist Phil Gingerich discovered a skull, dating back about 52 million years ago. Initially, it was thought to belong to a group of wolf-like carnivores called creodonts, but later comparisons showed similarities with the oldest known whale fossil, Archaeocetes. The fossil seemed to be the missing link between terrestrial mammals and whales.

The skull was dubbed, Pakicetus, and its most interesting feature proved to be the location of the ears. The ear region of the Pakicetus was located somewhere in the middle of the skull where you would normally find a land mammal's ears and those of a marine animal.

More recent discoveries include the Ambulocetus, Rhodocetus, and Basilosaurus. The Ambulocetus was an amphibian with fingers and hooves on the forelimbs but the hind feet were more adapted to swimming. It moved through the water by undulating, much like an otter.

The Rhodocetus is believed to be akin to a sea cow. Its ear region was more adaptive to underwater hearing and its hind legs were not attached to its pelvis.

Roughly 40 million years ago, the Basilosaurus may have been a fully adapted aquatic species, with strong flippers and a more flexible body, but it still retained the formation of weak, small hind legs. It was not able to walk on land.

All of these animals, though not proven to be direct ancestors of the whale, display evolutionary, whale-like features that may make them a part of the family tree.

The scientific advances in DNA technology and the unearthing of new fossils keeps bringing the original lineage of these, 60,000 million year old, majestically graceful, leviathans into question.

The exact evolutionary path of the whale is still being debated. Whether their ancestors were hoofed or finned, from the sea or the land, remains a mystery and adds to the human fascination and appreciation for these gentle giants.

More about this author: Dawn R. Cole

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