Arctic fossil shows how seals went from land to sea

23 Apr 2009, 3:03 am   -   Source: Reuters
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OTTAWA (Reuters) - Scientists in Canada's Arctic have discovered the fossil of a previously unknown web-footed carnivore that helps explain how seals developed from land-based mammals, a member of the team said on Wednesday.

OTTAWA (Reuters) - Scientists in Canada's Arctic have discovered the fossil of a previously unknown web-footed carnivore that helps explain how seals developed from land-based mammals, a member of the team said on Wednesday.

The very primitive animal, measuring around 110 cm (43 inches) from nose to tail, had a body similar to that of an otter, with a skull more closely related to a seal.

It lived in and around fresh water lakes about 20 million to 24 million years ago.

The mammal, named Puijila darwin, could move easily on both land and water and is a member of the pinniped family, which groups seals, sea lions and walruses.

The science team has dubbed it "a walking seal", although it is not the direct ancestor of any modern seal.

The most primitive pinniped previously discovered was Enaliarctos, an animal that lived around the same time but was already fully flippered and had a streamlined marine body.

"It (Enaliarctos) doesn't tell us anything about how that lineage came to be. We know they came from land mammals," said Natalia Rybczynski of the Canadian Museum of Nature.

"Our animal fills that transitional gap between the land form and the marine flippered form we're familiar with today," she told Reuters in an interview.

Details of the expedition will be published in the latest edition of Nature magazine.

The team found the fossil in 2007 during an expedition on Devon Island in the Canadian Arctic territory of Nunavut. Unusually, it is about 65 percent complete.

Puijila was a carnivorous mammal with large canine teeth, a short snout and a powerful jaw. It had an elongated streamlined body, webbed feet and a tail that enabled it to move through the water at speed.

The team -- which hopes to return to the Arctic this year to continue the investigation -- is particularly interested in why and how the Puijila came to lose its long tail.

"Other mammals that went from land to sea, like whales and manatees, retained and made good use of their tails, (which) became propulsive structures. For some reason the pinniped lineage didn't do that, and now we know they had had the option ... they had the tail but didn't use it," said Rybczynski.

Scientists had previously thought pinnipeds evolved from animals such as Enaliarctos, which lived along the western coast of North America and had gradually moved into the ocean.

"The idea hasn't been that there was this phase where they were living on the continent in streams and lakes. So that changes our idea about how these animals came to be," said Rybczynski. At the time, the Arctic was forested and much warmer than it is today.

One explanation could be that Puijila gradually moved further south, or that the animal found in the Arctic had come originally from the west coast. Parallel evolution -- the same process taking place in another part of the world at the same time -- is also a theory, said Rybczynski.

"We do have this most primitive form that we're finding in the Arctic so we also must consider the hypothesis that the Arctic was a place where these things could have been deriving from as well," she said.

(Reporting by David Ljunggren; editing by Rob Wilson)

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