Baleen whales: from sharp-toothed predators to gentle giants of the deep

While walking near the beach at Jan Juc in the late 1990s, teenage surfer Staumn Hunder found some fossilised bones poking out from limestone rock.

He and his father took the rock and bones – including a skull – to Monash University. The teenager had stumbled upon a strange, previously unidentified species of whale that swam in the Southern Ocean about 25 million years ago.

News of the weird new whale, which was named Janjucetus hunderi, reached Felix Marx, who was studying palaeontology in the UK at the time. 

“It was a skull of a very early ancestor of modern baleen whales, but it had teeth and it looked really bizarre,” he says. 

Modern baleen whales are the giants of the ocean, the largest animals to have lived. They range from pygmy right whales, which grow to just under seven metres, to right whales, humpbacks, grey whales and blue whales, which grow up to 30 metres and are the biggest whales of all. 

Evolution teaches us that mammals evolved from sea creatures. But whales are mammals that have re-entered the water – their closest modern ancestor is the hippopotamus. Going back to the ocean has not been an easy transition. 

“It's difficult for mammals to breathe while living in the sea,” Dr Marx says. “It's difficult to maintain your temperature, because water conducts heat away from your body; difficult to suckle your young, because they float away.”

Baleen whales differ from all other mammals because they have no teeth. Instead, they've evolved the hair-like structure called baleen that allows them to filter huge amounts of tiny plankton from seawater.

“Baleen is made from keratin, like your fingernails” Dr Marx explains. “These whales have a series of plates made from that material, like combs in their mouth.” 

As a student of evolution, the toothy Janjucetus sparked his interest because of the unusual way it had evolved. Unlike its living descendants, Janjucetus had no baleen, but it still had teeth – they were sharp and used to bite their prey. 

“In contrast to modern whales, it was quite small (3.5 metres, about the size of a bottlenose dolphin), and probably a ferocious predator,” Dr Marx says

The creature persuaded Dr Marx to study archaic whales. They were the subject of his master’s and PhD. Now, as a post-doctoral research fellow in evolutionary biology at Monash, he's still working out how modern baleens came to be.

The many ways in which whales adapted “really tell you something about evolution,” Dr Marx says. “The variety of anatomies that you can get, the variety of shapes. How animals can adapt to these really quite extreme circumstances, and how quickly.”

About 25 million years ago, whales finally lost their teeth and started to look more like their modern kin. Nevertheless, their story remains a mystery. 

“It's generally thought that these ancient whales belong to one or more of the living families, but they're so different from their modern cousins that no one is quite sure where they fit.” 

He recently helped identify an ancient Peruvian whale, Tiucetus rosae (pictured), that he believes is an early ancestor of the pygmy right whale – the only surviving member of its family. 

Nearly all of today’s whales are extremely large. Most smaller species died out “two-and-a-half, three million years ago”, with the beginning of the Ice Age, he says. 

“At that point you get a distinct turnover in the ocean ecosystem. These small whales disappear, and some of their predators disappear as well. Big sharks like megalodon, and the giant sperm whale, Livyatan, which had these massive, massive teeth.” (Liyatan was related to the modern sperm whale – the largest living predator – and was about the same size, around 16 metres. But where the modern animal only has teeth on the lower jaw, allowing it to feed on squid, Livyatan had upper teeth as well.)

With the disappearance of their smaller cousins, large whales were all that was left, and they thrived. 

“The large whales we see today are, in some ways, the result of the Ice Age.”

Dr Marx describes the great whales as “ecosystem engineers”. 

It's been proposed, for example, that before whaling, great whales ate 60 per cent of the food in the North Pacific alone. When whales go on their epic migrations from the poles to the tropics, their waste fertilises the ocean (whale poo is rich in iron), providing nutrients for plankton, krill and other marine creatures. 

Whales transport nutrients horizontally “across the ocean in ways that ocean currents, for example, don’t”, Dr Marx says. 

They also move nutrients vertically through the water column when they dive and breach, mixing the cold water from the bottom of the sea with the warmer water on top. And when whales die, their carcasses – known as whale falls – provide great feasts for bottom-dwelling creatures.

“The large whales we see today are, in some ways, the result of the Ice Age.”

What effect will climate change have on whales? 

Dr Marx says he doesn’t know. But he says it's been suggested that before whales became large, the oceans were “a lot more stratified than they are today” with warm water staying at the top and cold water at the bottom, “a bit like a stagnant pond”.

“So it’s a possibility that we could return to something like that,” he says. A less dynamic ocean, with fewer nutrients, and different – and perhaps fewer – living creatures.

As an evolutionary biologist, Dr Marx recognises that the planet and its creatures have always changed – “but never as rapidly as they are now”, he says. 

“We're forcing change not in a matter of millions of years, not even hundreds of thousands of years, but potentially hundreds of years or decades. It's really unpredictable, and a lot of stuff will presumably meet its end just because of that.”