The evolution of whales

In common with many people, I find whales to be the most fascinating of mammals, but had always wondered how and why they came to evolve. Here is their story...

The oldest known whale is Himalayecetus subathuensis, dating back to around 53 million years ago. As its name suggests, remains have been found in the Himalayas, in the Simla Hills of India, an area which was submerged in the Tethys sea during the Tertiary period. According to research, the animal may have been amphibious, spending much of its time on land. An earlier animal, Ambulocetus resembling the modern otter, had teeth and its pelvis was still fused to its spine, but at about 10 feet long, it was beginning to show the adaptations later associated with cetaceans.

The creature Pakicetus had pointed teeth and some adaptation to the inner ear for marine living, but still had four limbs, and no blowhole. Rodhocetus, another Ecocene creature, was becoming more like the whales we know today, with much shorter limbs (its femur only about 8 inches (20cm) long. Its snout was longer and toothed, and its pelvis was not fused to the spine. Dorudon atrox continued the trend, with flattened flippers, and greatly bout 20 feet (6 m) long. Its arms were small, flattened flippers. The rear limbs were vestigal, being about 4 inches (10 cm) long.

The baleen whales evolved during the late Oligocene period, the earliest known being Aetiocetus, which while it still had teeth, also had a loose jaw hinge like the later baleen whales, enabling them to eat in quantity.

These, the major milestones in whale evolution, still do not explain why the animals reverted to sea living. The suggestion has been made that food was at one time more plentiful in the sea, and that the rapid adaptation enabled them to find a niche in the marine environment. Whatever the truth, our fascination with whales continues.

http://www.enchantedlearning.com/subjects/whales/allabout/Evol.shtml
http://news.bbc.co.uk/hi/english/sci/tech/newsid_1553000/1553008.stm

In Pakistan, scientists have been examining newly-discovered fossils of ancient whales. The interesting part? These whales lived mostly on land. Paleontologists all over are talking about this, and trying to answer a question about ancestry. How did whales become marine mammals, and what was the evolutionary cycle that whales went through before actually being the whales we have today, and what other animals were most closely related to the whale?

Scientists like Philip D. Gingerich, a paleontologist at the University of Michigan, are trying to make the bridge between ancient land-dwellers and current-day whales. J.G.M. Thewissen, an associate professor of anatomy, discovered a group of fossils from 50 million years ago of a ancient land-dwelling whales called pakicetids in Pakistan, the area in which most scientists agree that the evolution between land-dwelling and marine whales took place. Scientists are finally understanding more clearly the evolutionary cycle that whales went through.

Surprisingly, this evolutionary cycle only took a period of about 8 million years. Scientists are able to make the connections between whales by examining their fossils and those of other prehistoric creatures. They have made connections of animal fossils that lead towards ankle bones in the whale. However, they have not been able to find any fossil specimens of whales with these ankles. Scientists assume that sharks had eaten the legs off these whales when they had died, so they are not fossilized with the rest of the whale. This year, Philip Gingerich found four new fossils of the prehistoric whales in an area where there was shallow water. This meant that sharks couldn’t get to the whales’ small legs, so they were fossilized and buried until recently. Now scientists are busy analyzing the whales’ ankles, and are discovering new secrets about prehistoric whales.

My Personal Response:

I was really surprised by these discoveries. I had never had any idea about where whales had actually come from. I had always just taken them for granted, as we do with so many other things. The thing that most surprised me about whales was the prospect of imagining a whale not only with hands and feet, but also being a somewhat wolf-like creature, one that had hooves and was a great runner. Somehow, I have trouble imagining a whale running quickly. Also, I never had any idea that whales would be in any way related to certain plant-eating land-dwellers. Imagining a whale and a hippo being related is one thing, but a whale and a sheep or a whale and a giraffe? It really is hard to grasp, and I am amazed at how these scientists can make the connections between these ancient animals.

References: 1. “Fossil Links Whales Back to the Land” in the Los Angeles Times by Usha Lee McFarling. (September 24, 2001)