When I was in primary school, one of my favourite books was Ted Hughes’ How the Whale Became. For children who persistently ask “why” about everything, Hughes provided tall tales to explain animal origins, using the bizarre logic that children’s fiction thrives upon. For example: the hare grew long ears to hear the answer to its marriage proposal to the moon. Well, naturally. These stories fuelled my imagination about animal origins, albeit in an absurdist Lamarckian fashion.

We now know, thanks to Darwin, Russel Wallace, and the many great scientists since, that living things don’t evolve traits in order to accomplish a goal. Traits that improve survival are passed along to an animals’ offspring. The hare didn’t grow his ears to listen for whispers from a high place, but an ancestor with bigger ears thanks to a random mutation, would have heard danger approaching before the other proto-hares. And so it survived to produce bigger-lugged babies.

Hughes’ choice of the whale is not unexpected: these enormous creatures have left mankind scratching their heads for centuries. Thanks to fossils from places such as Wadi El Hitan in Egypt – aka “Whale Valley” - the surprising voyage of the whale’s landlubber ancestors to the sea is well understood. But nature keeps her cards close to her chest: there are still plenty of mysteries for palaeontologists to solve. Not least is the origin of the whale’s “moustache”.

A section of baleen plates from a minke whale (Balaenoptera acutorostrata). Photograph: Elsa Panciroli

It may come as a surprise that whales and dolphins, collectively called cetaceans, are most closely related to the hoofed animals called artiodactyls. The latter include deer, pigs and hippos. At first glance, you may not see the family resemblance between Moby Dick and Babe, but you need to check out their ankles. Anatomists identified a unique shape in the astragalus (one of the ankle bones) of ancient proto-whales that still had hind limbs, a shape shared only with artiodactyls. Since the 1990s, examination of whale DNA has come to the same conclusion: these groups share a common ancestor. And so the taxonomic order Cetartiodactyla was named, amalgamating deer and dolphins.

Around 50 million years ago, cetacean ancestors took to the water. It’s not only those hoofy legs they’ve modified and lost in their consequent evolutionary journey. Half of the group kept their teeth, multiplying the number of pointy gnashers in their jaws to make them effective fish catchers. These are the odontocetes: including porpoises, dolphins and killer whales. The rest of the cetaceans however, abandoned their teeth – and donned a moustache.

This moustache is properly called baleen, and is found in the mystecetes: the group of whales that include the famous giants such as humpbacks, bowheads and blue whales. It is neither hair nor tooth, but a stack of keratinous plates that hang, closely packed and bristling, from the upper jaw inside a whale’s mouth, forming a brush-like sieve for feeding. Recent research suggests it evolved from the gums, but exactly when and how it first appeared in ancient whales is difficult to figure out. Baleen may have been around for up to 30 million years, but it almost never preserves in the fossil record. The oldest direct fossil evidence is only 8 million years old.

This is where Alfred comes in.



Digital reconstruction of the skull of ‘Alfred’ the Aetiocetid (fossil whale). Specimen held at the Museum Victoria, Melbourne. Illustration: Marx et al. 2016/Memoirs of Museum Victoria

A 25-million-year-old fossil whale from Washington State, specimen NMV P252567 – or ‘Alfred’ to his friends – belongs to an extinct group of whales called aetiocetids. This group of whales certainly still had teeth, but grooves and holes in their upper jaws suggest they had baleen at the same time. This combination of both has been proposed as a transitional state between possessing only teeth, and possessing only baleen. However, although this evolutionary step of baleen and teeth in the same whale has generally been accepted by palaeontologists, the mechanism by which an animal with such a mouthful ate its food has remained contentious.

“We are essentially rejecting the accepted model, which has been around for quite some time” Travis Park, co-author of a new paper out this week told me. “Alfred is the key to understanding the evolution of baleen.”

In this exciting study of the Oligocene age skull - reconstructed digitally by an international team from CT-scans - palaeontologists have challenged the idea of a baleen and tooth transitional stage in ancient whales.

Suction feeding in a fossil whale. Photograph: Marx et al., 2016/Memoirs of Museum Victoria

Travis told me Alfred’s story: “I had begun preparing this fossil in 2014, but it wasn’t until one of my co-authors, Tim Ziegler, began more intensive preparation of the specimen early this year that the teeth were first noticed. We realised that these marks could only be explained by abrasive material being sucked into the mouth, wearing down the teeth. Alfred was a suction feeder!”

Travis Park, Erich Fitzgerald, Tim Ziegler and Felix Marx with Alfred’s fossil, and a 3D print. Photograph: Benjamin Healley

The presence of scratches on the inner surface of Alfred’s teeth suggest he was rasping his tongue along the back of them when feeding. This is also seen in living marine mammal suction feeders such as beluga whales, leopard seals and fur seals. When feeding this way, sand particles and other hard debris sucked into the mouth along with their prey scratch the predators’ teeth, like needles on a vinyl record, leaving tell-tale marks in the enamel and dentine.



“If Alfred had baleen in its mouth, the teeth would have been shielded from this abrasive wear – so, no baleen in this one!” explains Travis. He and his co-authors argue that suction feeding in this manner would have been impossible if there were baleen plates getting in the way. This means Alfred only had teeth, and fed by suction rather than using them to chomp on fish. It is therefore possible that other, if not all, Aetoiocetids fed in this way.



What you don’t use, nature has a tendency to lose. If ancient whales like Alfred weren’t using their teeth to bite, over many generations the redundant teeth may have been lost, paving the way for the evolution of baleen from modified gum tissue.

The evolution of baleen in whales. Photograph: Marx et al., 2016/Memoirs of Museum Victoria.

“This suggests a new model for the evolution of baleen,” Park explained, “whales first switched from biting prey to suction feeding, which over time led to the loss of the now largely redundant teeth. Baleen then evolved somewhat later from the gums, to help hold prey in the mouth while water drawn in during suction was expelled.”

“The origin of baleen must lie much closer to the origin of toothless mysticetes” Park explained.

What would whales like Alfred have looked like? I asked Travis: “Alfred would have looked different to any whale alive today - something the size of a dolphin (around three metres long) but with a broad, flat snout instead of a bulging forehead.” He shared the reconstruction of this fossil whale feeding: “I imagine Alfred could have spent its time foraging on the seabed, sucking up small fish and squid.”

Reconstruction of fossil whale, an Aetiocetid nicknamed ‘Alfred’, suction feeding. Illustration: Carl Buell

The puzzle of baleen is still missing many pieces. The oldest fossils from the modern baleen whales come from around 20 million years ago, not long after Alfred swam the ancient seas. Such a radical change from biting teeth to fibrous moustachioed mouths would have required many generations of selective advantage leading to baleen, and huge changes in feeding behaviour. How this took place remains to be solved by future revelations from the fossil record - and the diligent work of the palaeontologists who study them.

In the meantime, we are left to wonder at the evolution of these giant moustachioed hipsters of the sea.

The discovery of Alfred and implications for the evolution of filter feeding whales.

References

Marx FG,Hocking DP, Park T, Ziegler T, Evans AR, Fitzgerald EMG. 2016 Suction feeding preceded filtering in baleen whale evolution. Memoirs of Museum Victoria, 75: 71-82.

Graur D, Higgins DG. 1994 Molecular evidence for the inclusion of cetaceans within the order Artiodactyla. Molecular Biology and Evolution, 11: 357-364.

Deméré TA, McGowan MR, Berta A, Gatesy J. 2006 Morphological and Molecular Evidence for a Stepwise Evolutionary Transition from Teeth to Baleen in Mysticete Whales. Systematic Biology, 57: 15-37.