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What ran like a wolf, but is related to the hippo, and now lives in the ocean? The answer: A Whale!

As this ScienCentral News video reports, the whale’s family tree now includes an ancestor with four legs and a tail.

More Q&A with paleontologist J.G.M. "Hans" Thewissen of the North Eastern Ohio Universities Medical College (NEOUCOM), whose research was funded by the National Science Foundation.

What’s important about these fossils?

I think there are two important things about these skeletons, the first thing that they tell us is what the ancestors of whales looked like, they were really land mammals. For these particular whales, pakicetus whales, in the past all we had for them were parts of the skull and parts of the teeth, we didn’t even have a complete skull, we had a brain case, that was all. Now we have the whole skeleton. From the skull, we knew that these were whales, that these have all features of the skull that make a whale. The teeth are very whale-like too, but we never expected that these animals would look like land animals, that they were living on land, because no whales in modern times do and all past whales, all extinct whales that have been discovered ever, were at most amphibious animals. This is a real land animal.

The second thing that’s important about these skeletons is not related to their body shape but to the anatomy of particular parts. When we studied the anatomy of the skeleton we really came to a surprising conclusion. In the past people always thought that whales were closely related to an extinct group of mammals called mesonychians, and mesonychians kind of look like hyenas. People who study DNA sequences had studied the same problem, but they all came to the conclusion that whales were very closely related to hippos, a very different idea from what people thought, like myself, paleontologists. The new skeletons that we have really have changed my mind and the minds of my fossil colleagues about the relations of whales and now it seems clear that the people who study DNA, the molecular systematists, were much closer to the truth than we were. So that’s the real big change in our understanding of what the brothers and sisters of whales are, really.

How can you be sure they are whales?

Unlike what you might imagine, the ear makes a whale. There are particular grooves and bumps on the bones of the ear of these whales, and all whales, that show that these are whales. The ear in modern whales is very important, you know, they echolocate for instance. And the particular bony features in the ear are present in all modern whales and all fossil whales but in no other mammal, so it was really the ear that pointed out for us that these animals that we have here were whales.

So whales went back to the sea? Isn’t that where we all came from?

It is true that life originated in the sea, then slowly moved on land, that happened about 320 million years ago, an animal that looked like a fish crawled on land and basically started to look something like a salamander. We’re talking about a transition that happened a lot more recently, the transition between a land mammal and a whale. That only happened 50 million years ago. So at that point life had been on land for a long time and the animals from which whales are descended were land mammals. They did breathing with their lungs, they nursed their young, they had live young that were nursed with mother’s milk. And modern whales are still like that, they just took those features back into the water with them.

What is it like to find a missing link?

I think the present discovery is different from many in that this is a discovery that was made over a number of years, we kept on finding more and more bones at this one site and it took us a long time to realize that these bones that we were finding were whale bones. Because what we found was not one skeleton of one individual whale, but we found bits and pieces of many different whales. So it wasn’t really a discovery like in the field you suddenly find a beautiful skeleton like happens at Jurassic Park, it was a very slow process of realizing that the bones which we had tons of actually went with the heads that were the whale heads.

The main way in which we made sure that was true was to look at the geochemistry of the bones. And the geochemistry of the bones was identical to that of the whale skulls we had and not to any of the other mammals at that locality.

This is a really big deal to scientists, but why should the general public care?

What we can learn from them about evolution, we know many instances in time when there has been some major change in a group of animals, for instance the ancestors of bats learned to fly, the ancestors of birds learned to fly, the ancestors of humans learned to walk on their hind feet only. However, for most of those transitions, the fossil record is very poor and that’s because it all happens very fast in one place on earth and you don’t really have all the intermediate stages. Now with these discoveries... for whales we have a very good series of intermediates between the land ancestor of whales and the fully aquatic whales like we know them now. It’s really an excellent fossil record with lots of little steps where you can slowly see the changes come in. So it’s really a very good example of evolution.

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