Cracking the case of the walking whale: an evolutionary whodunit

By Susan Teskey, director and writer, The Mystery of the Walking Whale

It was one of the biggest mysteries of evolution: how did four-legged land mammals evolve into whales?  

And how did a top team of paleontologists unravel this 50-million-year-old cold case?  

In The Mystery of the Walking Whale, a new documentary from The Nature of Things, host Sarika Cullis-Suzuki joins them on a search for answers that takes her from the tropical waters of the Caribbean Ocean to the sands of a desolate Egyptian desert.

It started with the discovery of a fossil in what is now Pakistan. It looked like a big dog or deer but what was it? Its hoofed toes provided a clue, but its teeth suggested it ate flesh. And what did this odd little animal have to do with the modern whales?

As any good sleuth will tell you, solving a mystery is about making connections.

The clue of the multiple stomachs

Joy Reidenberg is the Sherlock Holmes of the whale world. She's a comparative anatomist — a fancy way of saying she finds connections between animals that don't appear to have any (like hoofed animals and whales). 

In The Mystery of the Walking Whale, Reidenberg reveals that whales have multiple stomach chambers — just like land-based hoofed animals.  

That is not as strange as it might seem, she says, because they come from the same ancestors.  

"It's just a throwback to their terrestrial ancestry," says Reidenberg. "They've retained this evolutionary baggage of a multi-chambered stomach."

The clue of the ancient ear bone

It didn't seem like a lot to go on to connect the animal they called Pakicetus to whales. Then scientists found the smoking gun: a tiny ear bone called the bulla, used for hearing underwater. Pakicetus had one, so it's likely that it spent a lot of time underwater. 

But only one other group of animals in the world have a bulla: whales! 

The little hoofed mammal is actually one of the earliest whales ever found. It was a mind-blowing discovery. Still, Pakicetus is a long way from being a modern whale. The case was far from solved. 

That's when the God of Death showed up.

In 2021, Egyptian paleontologists discovered discovered a new species of prehistoric animal. 

They called it Phiomicetus anubis, named after the Egyptian God of Death, because if you were unlucky enough to encounter one alive, it was game over. But what kind of creature was it? 

The clue of the misplaced nostril

All they had was a 43-million-year-old pile of bones. But that little pile contained the skull, and the jaw, teeth and sensory organs can provide crucial evidence to an animal's identity. 

A CT scan showed Anubis's nostrils weren't at the end of its nose like most mammals, but had moved back along the top of its snout — toward the position of a modern whale's blowhole. Could Anubis be a missing link between land animals and fully aquatic whales?

The clue of the shrinking vertebrae

Most of Anubis hadn't been found, so paleontologists didn't have a lot to go on. But they got lucky. One of the other bones was a neural spine, part of the thoracic vertebra that supports the muscles for the front limbs. In big four-legged animals, like cows, it's very long. In dolphins, who aren't known to do a lot of walking, it's very short.  Anubis's neural spine length? Halfway between the two. 

Anubis was a missing link — an elusive walking whale who lived both on land and in the water.

A few million years later, "King Lizard" slid into the picture.

At first, the scientists who discovered the fossils thought it was a giant dinosaur. At 20 metres long and weighing more than six tonnes, it was an aquatic killing machine with jaws powerful enough to crush anything in its path. Scientists called it Basilosaurus, or King Lizard. 

But the King should have kept his big mouth shut because, as is so often the case in mysteries, it's what gave him away.

The clue of the many molars

When paleontologists took a closer look at the fossils, they discovered this was no lizard.

Basilosaurus had a full set of incisors, canines, premolars and molars; types of teeth lizards don't have, but mammals do. Basilosaurus was a marine mammal — an early ancestor of today's whales.  

This was the first of the secrets the King Lizard was going to spill.

The clue of the little legs

This time scientists had a complete skeleton of Basilosaurus. Waiting for them at the other end of the beast was a giant surprise: a pair of tiny leg bones. They would have been useless for walking — so what were they doing there?  

Our Sherlock Joy Reidenberg says they are remnants of the hind legs their land-based ancestors once used. All modern whales still have a tiny pelvis. The clues to solving the mystery are written within their bodies.

The clue of the switched-off genes 

What's a cold case investigation without up-to-the-minute DNA analysis? It turns out that whales have some surprising genetic material for animals who live in the water. 

They still have genes for sweating, making saliva, seeing colour and smelling — genes that are no longer active, but are giveaways that whales once lived on land. 

And genetic comparisons between whales and hoofed animals also reveal a very surprising closest living relative. All clues that reveal the true origin of whales.

The clue of the whale's tail

While watching whales off the coast of Dominican Republic, Cullis-Suzuki shows off her own detective skills. As a marine biologist who has mainly studied fish, she spots a crucial difference in the way whales move through the ocean. 

"I'm noticing [that] unlike fish, whose tails move side to side, these whales' tails move up and down. Totally different!" she says.

"Because they derive from a land animal!" says Reidenberg. "When whales entered the water they kept the up-and-down spinal movement that they had on land. And now they are essentially galloping through the ocean." 

Is this the clincher? Is this cold case closed? Watch The Mystery of the Walking Whale on CBC Gem.