New Species of Ancient Whale Offers Clues on How Whales Evolved to Swim

Scientists have discovered an entirely new species of ancient whale that existed 35 million years ago—and it could provide clues to how whales today evolved to swim.

A paper published in open-access journal PLOS ONE describes a well-preserved specimen of a species newly named Aegicetus gehennae. It is the youngest known example of a group called the protocetids from the Eocene epoch. These are early whales and the precursors to today's cetaceans, but unlike those around today, protocetids were only partially aquatic.

Most protocetids are thought to have used limbs to swim, somewhat like a modern-day amphibian. While they are thought to have fed in the water, it is believed they returned to land to sleep.

This particular species has been named after the discovery of two specimens in 2007 in the "Valley of the Whales" at the Wadi Al Hitan UNESCO World Heritage Site, in Egypt. While one is only the partial remains of an animal, the other is a complete skeleton—making it one of the best-preserved ancient whales out there, the researchers say.

Research suggests it was most likely a male that would have weighed around 890 kilograms, which is about twice as heavy as a grand piano.

Aegicetus gehennae is believed to have looked similar to the Basilosaurus, ‘King of the Lizards’ (pictured). dottedhippo/iStock

The newly described Aegicetus gehennae is the 22nd known species of protocetids, a family of cetaceans that spanned the areas around Africa, Asia and the Americas. (They may have existed in Europe, Australia and Antarctica too, but there aren't the fossils to prove it.)

"Early protocetid whales living 47 to 41 million years ago were foot-powered swimmers, and later basilosaurid and modern whales—starting about 37 million years ago—were tail-powered swimmers," write the study authors.

Aegicetus gehennae stood somewhere in-between. It was a species that straddled on the transition from foot-powered swimming to tail-powered swimming—an observation researchers made from the proportions of its skeleton. It had a longer body and tail than its forebearers and smaller legs. The researchers also point to the connection between the hind legs and the spinal column, which seems to be looser than those of species that were less fully aquatic.

The researchers compare the Aegicetus gehennae to another species that would have lived around the same time, the Basilosaurus (nickname: 'King of the Lizards'). Both animals (and others alive at the time) would have swum by undulating the middle of the body and the tail in a similar fashion to the crocodiles of today, a movement that may be a key feature in the transition towards tailed-powered swimming.

cervical and thoracic vertebrae of Aegicetus gehennae
These are cervical and thoracic vertebrae of Aegicetus gehennae type specimen (CGM 60584). Gingerich et al., 2019