Seal With "Arms" Discovered -- Evolution at Work

Brian Handwerk
for National Geographic News
April 22, 2009

A newly discovered prehistoric seal with "arms" is the no-longer missing link between seals' land-based ancestors and the ocean-dwelling, flippered creatures we know, a new study says.

Perhaps spurred by amplified global warming and cooling in the ancient Arctic, the freshwater, amphibious seal is an example of the region as a hotbed of evolution, researchers say.

( PHOTOS: 7 Major "Missing Links" Since Darwin.)

Measuring about three and a half feet (110 centimeters) long, the 20- to 24-million-year-old "walking seal" had heavy, muscular limbs like those of a land mammal, a long tail, and webbed feet.

Unlike the shuffling seals of today, the newfound species may have walked as gracefully as it swam, researchers say.

If the finless seal looks slightly less than odd, it may be because of its resemblance to a modern otter, which lead study author Natalia Rybczynski agreed "to some extent, ecologically" could be "a modern analogy for these early pinnipeds."

Pinnipeds—literally "fin feet"—include walruses, seals, and sea lions.

Seal-ing the Evolutionary Gap

Many marine mammals, such as whales and manatees, are believed to have roots on land—an idea that originated with Charles Darwin 150 years ago.

But hard evidence for land-to-water evolution in seals and other pinnipeds was lacking until the new discovery—aptly named Puijila darwini ("Darwin's young marine mammal" in an amalgamation of an Inuit language and Latin).

"We know that some sort of land-dwelling ancestor existed, but how did we get to the fully marine form?" asked Rybczynski, a vertebrate paleontologist with the Canadian Museum of Nature.

"There was a morphological gap. So Puijila darwini is an important transition fossil," Rybczynski added.

Evolution on Fast Forward

The most primitive pinniped fossil skeleton yet found, the P. darwini specimen was discovered in 2007 in an impact crater in the Canadian Arctic.

The inland location on Devon Island, Nunavut, suggests that pinniped evolution featured a freshwater phase, according to the study.

During that period the animals frequented the then temperate Arctic's lakes and rivers. The species may have gradually adapted to an ocean lifestyle after lakes had begun to freeze over in winter, depriving the seals of food.

This first evidence of early Arctic pinnipeds suggests that the region may have been a hotbed of pinniped evolution, Rybczynski said. The Arctic experiences amplified climate shifts, which could speed evolution as animals are forced to adapt—or disappear.

Findings to be published in tomorrow's issue of the journal Nature.




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