Earliest fossil seal found

Researchers have found a fossilized ancestor of modern seals and sea lions that they say represents an evolutionary step in the organisms' transition from land-dwelling mammals to the aquatic creatures they are today. The fossil skeleton is thought to be more than 20 million years old, making it the earliest fossil pinniped -- the taxonomic name for seals, sea lions and walruses -- yet discovered, they report in the latest issue of __Nature__.

An artist's recreation of
__Puijila darwini__
Illustration by/courtesy of
Mark A. Klingler of Carnegie Museum
of Natural History (CMNH)

The nearly-complete fossilized skeleton of __Puijila darwini__, which probably had webbed feet and a long tail and looked something like an otter, turned up on a small island in the Canadian Arctic where scientists have found other fossil mammals deposited about 20 million years ago. "We're interested in the land-to-sea transition," linkurl:Natalia Rybczynski,;http://www.carleton.ca/biology/people/adjuncts/rybczynski/ a paleobiologist at the Canadian Museum of Nature and lead author of the paper, told __The Scientist__. "Our animal becomes important because he helps fill that transitional gap." The fossilized skeleton has flattened finger and toe bones, which suggests that its feet were webbed, but has forelimbs and other skeletal features more akin to those of modern bears, otters, and skunks. This mishmash of characteristics may help paleontologists reconstruct some of the evolutionary changes that pinniped ancestors underwent. "We have a spotty record of this transition," linkurl:Annalisa Berta,;http://www.bio.sdsu.edu/faculty/berta.html an evolutionary biologist at San Diego State University who was not involved with the study, told __The Scientist__. "[__P. darwini__] is going to help us sort out the order that key pinniped characteristics were acquired." Until now, the most primitive pinniped fossil found was __Enaliarctos__--a flippered genus of seal that inhabited the western shores of North America some 20 million years ago. __P. darwini__ is likely not a direct ancestor of modern pinnipeds but rather an early branch on the pinniped family tree, Rybczynski said. "This is a missing link as opposed to the missing link."

__Puijila__ skeleton laid out.
Photo by Martin Lipman.

The physical characteristics and geographic location of __P. darwini__ suggest that ancient pinnipeds may have made an evolutionary stopover in freshwater habitats in their march towards the sea. Rybczynski noted that the name that she and her colleagues named the find after Charles Darwin because he hypothesized this was the case for marine mammals "A strictly terrestrial animal, by occasionally hunting for food in shallow water, then in streams and lakes, might at last be converted into an animal so thoroughly aquatic as to brave the open ocean," Darwin wrote in an early version of __On the Origin of Species by Means of Natural Selection__. (__Puijila__ is Inuktitut--the language spoken by Inuit tribes in the area of the find--for young sea mammal, Rybczynski added.) __P. darwini's__ Arctic resting place makes it the first fossil pinniped to be found at such a high latitude, prompting the authors to suggest that northern latitudes may have been the setting for more critical evolutionary events in the history of modern organisms than is currently supposed. "The Arctic may be an important place for evolution as well," Rybczynski said. Berta, however, is not so sure. Other fossil pinnipeds have been found throughout Eurasia and in the North Pacific, she said, and the current find doesn't necessarily mean the Arctic is pinnipeds' ancestral home. Without additional evidence, she said, "it seems more likely to me that the Arctic was an isolated area that's maybe not the center of radiation for this group."

Illustration by 3D Animator/illustrator Alex Tirabasso.
Copyright Canadian Museum of Nature.

linkurl:Tom Demere,;http://www.sdnhm.org/research/paleontology/demere.html a paleobiologist at the San Diego Natural History Museum, said that the find is important because paleontologists had identified few transitional pinniped fossils prior to unearthing __P. darwini__. The fossil gives scientists "direct evidence of this mosaic of the terrestrial and aquatic features" that pinnipeds possessed as their ancestors morphed into ocean-going creatures and traded paws for flippers, he said. Rybczynski's team of Canadian and American researchers uncovered __P. darwini__ by a fortuitous accident. The group was hunting for fossils in an ancient lake bed on Devon Island in the vast territory of Nuanvut in 2007, when an all terrain vehicle (ATV) the scientists were using to traverse the harsh landscape ran out of gas. While Rybczynski and a photographer ran two or three kilometers back to camp, other scientists who had remained with the stranded ATV noticed blackish bones strewn about on the ground. When she returned, her colleagues were doing the "fossil dance"--a signal the team devised to alert one another to a find. "For all your planning," Rybczynski said, "sometimes it all comes down to luck."
**__Related stories:__***linkurl:The Disputed Rise of Mammals;http://www.the-scientist.com/article/display/55302/
[January 2009]*linkurl:Ancient fingers and toes;http://www.the-scientist.com/blog/display/55022/
[21st September 2008]