Whale evolution from walking whales to Janjucetus

Transcript

Although whales swim in the sea and superficially look like fish, they are not. Whales are mammals like us; they suckle their young, give birth to live young and even have hair. So if whales evolved from land living mammals, how did they evolve from them?

Well the answer to that question is a short one: food. The sea provides a rich bounty of resources that an enterprising mammal might take advantage of. Fifty-five million years ago a small, deer-like hoofed mammal took the first tentative steps back into the water. By 48 million years ago whales were already readily adapted for life in the water but they still had to go back on land to mate, give birth and suckle their young. An example of one of these early amphibious whales is Ambulocetus, a scientific name which literally means the ‘walking whale’.

Whales and dolphins eventually evolved the ability to mate and give birth and suckle their young underwater. Once this critical step had been taken in their evolutionary history there was no need to return to the land. The skeleton of whales changed. This remarkable change can be seen in Dorudon where the bones of the pelvis and the hind limb detached from the vertebral column. What that meant is that whales could no longer bare their weight on land and were forever after purely swimmers of the seas.

Those whales that evolved to exploit these newly abundant food resources in the ocean were the two groups of modern whales and dolphins: the toothed echo-locating whales and the gentle giants, the immense baleen whales. Baleen whales have their origins at about 34 million years ago and it is in fossils in Victoria that we see the very first glimmerings of this evolutionary heritage.

Meet Janjucetus. Janjucetus is a spectacular fossil discovered in the late 1990s near Torquay here in Victoria.

Janjucetus is not only a beautiful fossil, it’s a beautiful example of a transitional form between the ancient Dorudon and the modern baleen whales such as the Blue Whale as you can see behind me here.

About this Video

Erich Fitzgerald, Museum Victoria, explains some of the key moments in whale evolution.
Length: 02:32
Photograph of a yellow plastic Tyranasaurus Rex