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Top: Reconstruction of <em>Ambulocetus natans</em>, a primitive cetacean from 40-50 million years ago, by <a href="http://spinops.blogspot.com">Nobu Tamura</a>, CC <a href="http://en.wikipedia.org/wiki/en:GNU_Free_Documentation_License">some rights reserved</a>, and Bottom: Reconstruction of <em>Kutchicetus</em>, another ancestor of today's sea mammals.
Top: Reconstruction of Ambulocetus natans, a primitive cetacean from 40-50 million years ago, by Nobu Tamura, CC some rights reserved, and Bottom: Reconstruction of Kutchicetus, another ancestor of today's sea mammals.

Natural Selections: Whales and land mammals

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Whales are relatively new to the ocean. Fossil evidence allows evolutionary biologists to trace the whale's transformation from land mammal into air-breathing ocean dweller. Today's whales still carry a legacy of their landed past in a vestigial pelvis, femur, and other typical anatomical traits. Martha Foley and Dr. Curt Stager dig into a big topic.

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Unlike humans and other mammals, which evolved from sea animals into land dwelling species, whales went in the opposite direction. “It sort of seems to run against the preconception a lot of people have that evolution is this one direction thing. Stuff sort of changing to become more and more like us, I guess you could say.”

However, it makes sense to an evolutionary biologist, says Stager. They believe that wherever there is an opportunity for a species to make a living, something will “move in and do it.” If there was a niche in the water, something will adapt to survive there.

There are several things that support the idea that whales used to live on land. Like land mammals, whales are warm blooded, air breathing and produce milk for their offspring. Looking at the skeleton, there is a pelvis, which could indicate that there were back legs at one point. However, whales only have a tail, so the pelvis serves no purpose. “It’s a vestigial, or left-over body part.”

There are several intermediate species in the fossil record where it can be seen that whales go from land to water mammals. The back legs get shorter and finally disappear, the snout gets more elongated, and the nostrils move to the top of the head, becoming a blowhole. Their front flippers have bones, which resemble the same bones in our forearms.

Recently, there have been fossil finds from Pakistan and Southern Asia that support this idea. “There are some land walking mammals that people have long speculated were the ancestors of whales.” Whale evolution, or as some would say, “devolution,” has occurred over millions of years.

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