The First Whales

A look back in time at the evolution of whales with the Smithsonian’s Nick Pyenson

Nick Pyenson is Chair of the Paleobiology Department and Curator of Fossil Marine Mammals at the Smithsonian’s National Museum of Natural History. He is also the author of Spying on Whales and co-author with Alex Boersma of The Whale Who Swam Through Time.

It's a bright, breezy afternoon at the beach, and you can see the horizon where teal waves meet aquamarine sky under slow, puffy clouds. Closer to shore, there’s an animal that looks for all the world like a dog, darting in between the waves. You step carefully towards it and see that it has narrowly spaced eyes, a muscular neck, and a long snout bristling with teeth. Suddenly, you realize it's no dog, and you're standing on a bygone shoreline: You're watching one of the earliest whales, a four-legged Pakicetus, on the shores of the Tethys, an equatorial seaway that once stretched from modern-day Spain to India. This early whale snaps a fish from the surf and trots off, wagging its tail.

This reverie might have happened about 50 million years ago, and the only reason we know has to do with the fossil record. There are a lot of ways to tell the story of whale origins, but I’m a paleontologist, so I tend to favor storytelling with the fossilized skeletal evidence in hand. You might be surprised, but whales have an excellent fossil record, which makes it possible to trace how they evolved from land-dwelling four-legged animals to the streamlined mammals that swim alongside us and feature so prominently in our culture. 

Let’s start with those hind legs. You won’t find them in today’s whales, but paleontologists have found them in the earliest whale lineages. For early whales like Pakicetus, these hindlimbs were robust, fully capable of holding up the animal’s body weight. Moreover, the shape of their pelvis and the unique discovery of a fossilized fetus in a skeleton of Maiacetus suggest that these early whales gave birth on land, head-first, unlike today’s whales. Eventually, about 45 million years ago, some early whale lineages started reducing their hindlimbs, disconnecting their pelvis from their backbone, and evolving tail-propelled locomotion. Rather than paddling with their fore- and hindlimbs, these tiny-legged early whales were the first true ocean-going whales. If you get a chance to walk through the Ocean Hall at the Smithsonian, you’ll see a terrific example in the skeleton of Basilosaurus, a nearly 50-foot-long early whale with feet smaller than your hands. (Why this species has a dinosaur-sounding name is a story for another time.) 

Forelimbs tell an evolutionary story with a different outcome: As whales evolved aquatic lifestyles, their hands became more paddle-like. Pakicetus and Basilosaurus could move their elbow joints, but only Basilosaurus had a forelimb built for moving through the water. Eventually, whales evolved a fixed elbow joint along with arm proportions that made their forelimbs (or flippers) more like the aileron, rudder, and elevator of a plane: surfaces that control the physics of how a body rotates in a fluid. If you watch a video of a humpback whale or a dolphin, you’ll see how small movements in their flippers have a big impact.

When they smiled, the first whales on the planet looked nothing like their descendants today: They all had the kind of upper and lower teeth that you find in many other land mammals, including ourselves. Teeth, after all, are made of minerals, so they readily fossilize and can tell you a lot about their owner. The fossils of the incisors, canines, premolars, and molars of early whales are beautiful because of their preservation and wonderfully ornamented shapes — you can caress the blade-like edges of the cusps that must have sliced thousands of meals from the sea. 

Photo by Gabi Scott | Unsplash

But whales didn’t keep those teeth, and today’s whales tell us that a lot of evolutionary history has happened since the time of Basilosaurus. Some, like filter-feeding baleen whales, don’t have teeth at all; others, such as dolphins, killer whales, and other toothed whales, have a uniform row of pegs or sometimes only a tusk or two. Toothed whales also evolved underwater biosonar in the time since Basilosaurus. Like filter-feeding, these evolutionary innovations have only a few parallels in the history of vertebrates, making whales especially interesting for evolutionary biologists. More fossils will surely help.

Back in the Ocean Hall at the Smithsonian, Basilosaurus forms a diptych next to a full-size model of Phoenix, a North Atlantic right whale alive right now, and currently a grandmother. Right whales in the Northern Hemisphere have not really recovered from whaling and now contend with a very busy, noisy, and perilous ocean alongside us. Both whales on display tell us different sides of extinction. One seems inevitable over millions of years, while the other is in our control, especially if we make the most of our decisions in the coming decades. As much as I value fossil whales, a world full of living whales is a far better deal for everyone.

Feature image by Rahul Chakraborty | Unsplash