Transitional seal fossil

A major transitional fossil has been found. It’s a seal ancestor, 23 million years old. It a walking seal that looks a bit like an otter.

Puijila darwini

This is the oldest fossil of an ancestor to seals that has been found. Pujilla means “young sea mammal” in the Inuktitut language as spoken near where the fossil was found, on Devon Island. The species name darwini honours Charles Darwin. The great biologist hypothesized that land mammals would be likely to adapt to fresh water first and only later take to the sea. Pujilla, found in sediments laid down in a fresh water environment, is evidence for that hypothesis.

“The find suggests that pinnipeds went through a fresh water phase in their evolution,” said Natalia Rybczynski from the Canadian Museum of Nature (CMN) in Ottawa, who led the fieldwork.Pinnipeds are the seals, sea lions, and walruses. (Manatees returned to the water in a separate adaptation.)

“It also provides us with a glimpse of what pinnipeds looked like before they had flippers.”

The skeleton was about 65% complete, which enabled the researchers to reconstruct what the animal would have looked like in remarkable detail.

The legs suggest it would have walked upright on land; but the foot bones hint strongly at webbed feet.

The fossil was found in a former crater lake. Scientists have also found fossil fish from the same period, which may have been prey for the semi-aquatic seal.

“The remarkably preserved skeleton of Puijila had heavy limbs, indicative of well developed muscles, and flattened phalanges (finger or toe bones) which suggest that the feet were webbed – but not flippers,” said Mary Dawson from the Carnegie Museum of Natural History in Pittsburgh, US, another of the scientists.

The teeth indicate that the animal was a carnivore.

Until now, the most primitive fossil pinniped was a creature called Enaliarctos that dates from about the same period and appears to have lived in the sea along the northwestern coasts of North America.

Enaliarctos had flippers, but may have had to bring its prey to the shore for eating, whereas modern pinnipeds manage it at sea.

Intriguingly, different species of present-day seal swim in different ways – either rotating their flippers, or waving their hind-quarters from side to side, using the hind limbs for propulsion.

Enaliarctos appears to have been capable of both modes of swimming – and as a four-legged animal with four webbed feet, Puijila is a logical fore-runner of this creature which could swim with all four limbs.

This discovery suggests that seals, sea lions, and walruses evolved in the Arctic, and northern Canada and northern Russia likely places to look for more ancestral seals.

Brian Switek at Laelaps has detailed information from the actual paper in Nature.