Fossil of the World's Oldest Fur Seal Links a Gap in Seal Evolution

Scientists may have uncovered a missing link in seals. They've discovered the oldest known fur seal, which resolves a more than 5-million-year gap in fur seal and sea lion evolutionary history.

The researchers discovered a fossilized partial jaw, with several well-preserved teeth. It was found in a 15 to 17-million-year-old rock formation in Southern California in the early 19802 but until now, was misidentified as belonging to a walrus species. Now, researchers have taken a closer look at the fossil and have found that it actually belonged to a 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 to 12 million years ago," said John Cooper, one of the researchers, in a news release. "Yet we know that their fossil record must go back to around 16 to 17 million years ago or so, because walruses-the closest modern relative of the otariids-have a record reaching back that far."

The fur seal species was likely tiny. In fact, adults were only slightly larger than a sea other and around the size of a juvenile New Zealand fur seal. This particular species helps show the transition over these years and shows fossil evidence for the first five million years of fur seal and sea lion evolution.

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

The findings reveal a bit more about the evolution of these seals. As to why so little fossil evidence has been found thus far, it's possible that the earliest fur seals lived in the open ocean and only rarely strayed into continental shelf areas.

The findings are published in the journal Biology Letters.

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