Walrus Fossil Turns Out to Be Oldest Known Fur Seal

While searching among fossil collections in a California paleontological center, a PhD student in geology came upon a fossil that would soon fill a huge gap in scientists' understanding of sea lion and fur seal evolution.

Robert Boessenecker, of New Zealand's University of Otago, was browsing the collections at the John D. Cooper Archaeological and Paleontological Center in Orange County, Calif. when he came upon a fossil of a partial jaw alongside several well-preserved teeth. The samples were discovered in the early '80s and came from a rock formation in Southern California that was about 15 to 17 million years old.

While credited to the small walrus Neotherium, Boessenecker recognized right away that the remains were actually those of an early, very small, fur seal. Its real identity was welcome news.

"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," Boessenecker said in a release.

"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 added. "Until now we had no fossil evidence for the first five million years of fur seal and sea lion evolution."

Boessenecker said the fur seal fossil is a key transitional piece because of its teeth. They're in a middle ground between the simplified teeth of today's sea lions and the complex "bear-like" teeth found in the earliest pinnipeds (the scientific group name that includes all seals).

The creature itself was very small, with adults just a bit bigger than a sea otter and roughly the size of a juvenile New Zealand fur seal.

While the discovery of this earliest fur seal is satisfying, a question lingers, Boessenecker noted.

"The mystery remains of why there has only been one of these fur seals ever found, given that there have been extensive fossil excavations of similarly aged rocks in California," Boessenecker said.

The answer may come from an earlier proposal by Japanese palaeontologist Naoki Kohno, who suggested that the earliest fur seals made their living in the open ocean rather than in continental shelf areas, where preservation of their remains would have been more likely.

Read more at Discovery News