Oldest Known Fur Seal Discovered, Ends 'Ghost Lineage'

The oldest known fur seal to date has been discovered, dating back 15-17 million years ago and finally ending the mystery of the "ghost lineage," a new study says.

This new genus and species of fur seal is called Eotaria crypta, the genus Eotaria meaning "dawn sea lion." It is described in the journal Biology Letters.

Until now, there has been a more than 5-million-year gap in the fur seal and sea lion evolutionary history. That's because since E. crypta was first found in Southern California in the early 1980s, it has been mistaken as belonging to a walrus species. Now, scientists have finally seen the error in their ways.

Way back when E. crypta was roaming the seas, it was considered a tiny species, with adults being only slightly larger than a sea otter and around the size of a juvenile New Zealand fur seal. And when co-lead author Robert Boessenecker, from New Zealand's University of Otago, first laid eyes on the new species, he instantly realized that it was not the small walrus Neotherium but a tiny, early fur seal.

"This was very exciting as fur seals and sea lions - the family Otariidae - have a limited fossil record that, up until now, extended back to about 10-12 million years ago. Yet we know that their fossil record must go back to around 16-17 million years ago or so, because walruses - the closest modern relative of the otariids - have a record reaching back that far," he said in a press release.

In paleontology, this kind of gap is known as a "ghost lineage," and thanks to E. crypta, scientists can now "give up the ghost," so to speak.

So how did Boessenecker realize that he was looking at a fur seal and not a walrus? The answer lies in the new species' teeth, which are intermediate between the simplified teeth of modern sea lions and the complex bear-like teeth of the earliest known pinnipeds (including the family Otariidae).

And besides that, how come this is the first, and only fossil record of E. crypta ever found. Researchers can't be sure, but they speculate that the earliest fur seals lived in the open ocean and only rarely strayed into continental shelf areas, where they would be more likely to be preserved as fossils.

Regardless, the new study remedies a longstanding error in the evolutionary record of fur seals, and puts the ghost stories to rest.

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