Evolution Of Whales

We know more about the universe outside our solar system than we do about the depths of our own ocean.

- Josh Trosvig, Captain of Fishing Boat in Alaska

We know that dogs evolved from wolves, chickens are the closest relative of dinosaurs  and sapiens from apes. But evolution of whales, the largest mammal is not common knowledge. 

Whales are among the largest animals to ever exist on Earth, with some adult blue whales reaching 180 tonnes, nearly 21 times the weight of a Tyrannosaurus rex. And the long history of whales, which spans more than 50 million years, is chock-full of surprises. The earliest whales lived near water—but not in it—and they looked very different from the whales we know today. Pakicetus, for example, was a wolf-sized animal with four legs, a long snout, and a big tail. It hunted small prey along the coastal margins of Pakistan some 50 million years ago. But what links Pakicetus and the other early whales to modern cetaceans is a distinctive anatomical feature they all share: a bulbous structure in their ears known as an involucrum. This ancient structure may assist today’s whales and dolphins in hearing underwater. Early whales also had distinctive double-pulley ankle bones seen only in even-toed hoofed mammals, like camels and cows, which are now understood to be whales’ closest relatives.

As cetaceans evolved, forelimbs became flippers, nostrils shifted back to become blowholes, and legs eventually disappeared. It took whales about 10 million years to transition from land to sea, and they may have done so for a variety of reasons, which include escaping predation on land and capitalizing on abundant marine prey. But once whales were completely aquatic, they spent the next 40 million years adapting fully to life in the ocean. For much of this time, most cetaceans were little bigger than a humpback whale. Then, beginning around 4.5 million years ago, whales underwent another remarkable transformation. Many began bulking up dramatically, eventually reaching their current extreme sizes. That allowed them to bump up the amount of prey they consumed in one gulp, swim vast distances to reach places with abundant food sources, and fight off most marine predators.

That’s the basic, broad trajectory, but huge gaps remain in our knowledge of whales—including how baleen evolved in some species. And that’s where whale fossils come in. Fossil bones preserve enormous amounts of information, and whale fossils from the Oligocene era are particularly valuable, given the many changes that cetaceans went through at that time. The trouble is that marine fossils from that era are exceedingly difficult to find in most parts of the world. Sea levels during the Oligocene were much lower than today, so fossilized marine life from that time tends to lie deep beneath the ocean—beyond the reach of paleontologists.

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