Fossils at the John D. Cooper Archaeological and Paleontological Center once thought to belong to Neotherium mirum, an extinct species of basal walrus, have been reclassified as those from an ancient fur seal species -- filling in a 5 million-year gap in the evolutionary history of fur seals and sea lions.
The fossils -- newly identified by Robert Boessenecker from New Zealand's Otago University and Morgan Churchill from the University of Wyoming -- belong to a newly identified species and genus called Eotaria crypta.
The fossilized jaw bones and teeth were first retrieved from a 15 million- to 17 million-year-old rock formation in Southern California in the early 1980s. There were misidentified and have sat mostly unstudied in a museum collection in California for the last few decades.
Modern fur seals and sea lions belong to the family Otariidae. The closest relatives to the family include a variety of ancient walruses that scientists have found stretching back 16 million or 17 million years. But until now, researchers had only been able to find walruses' relatives, fur seals, dating back 10 million to 12 million years. The missing 5 million years was known as a "ghost lineage" -- a gap in the evolutionary timeline.
Now, with the proper identification of Eotaria crypta, that gap is plugged.
"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 in a press release.
Some scientists posit that the absence is due to the fact that ancient fur seals stuck to the open ocean, unlike today's species, which hug the beaches and rocks along the coast.
The new species is detailed in the latest issue of the U.K. Royal Society journal Biology Letters.