5 lecture

Narrator：Listen to part of a lecture in a Marine Biology Class

Professor：We know whales are mammals and that they evolved from land creatures. So the mystery is figuring out how they became ocean dwellers.

Because until recently there was no fossil record of what we call "the missing link"- that is evidence of species that show the transition between land-dwelling mammals and today's whales.

Fortunately, some recent fossil discoveries have made the picture a little bit clearer. For example, a few years back in Pakistan, they found a skull of a wolf-like creature. It's about 50 million years old.

Scientists had seen this wolf-like creature before, but this skull was different. The ear area of the skull had characteristics seen only in aquatic mammals, specifically whales.

Err, well, then also in Pakistan they found a fossil of another creature, which we call Ambulocetus natans That's muffle lay. The name Ambulocetus natans comes from Latin of course, and means "walking whale that swims".

It clearly had four limbs that couldn't have been used for walking. It also had a long thin tail, typical of mammals, something we don't see in today's whales.

But, it also had a long skeletal structure. And that long skeletal structure suggests that it was aquatic. And very recently in Egypt, they found a skeleton of Basilosaurus.

Basilosaurus was a creature that we've already known about for over a hundred years. And it has been linked to modern whales because of its long whale-like body. But this new fossil find showed a full set of leg bones, something we didn't have before.

The legs were too small to be useful. They weren't even connected to its Power San and couldn't have supported its weight. But it clearly shows Basilosaurus an evolution from land creature.