After more than thirty years filed away in the John D. Cooper Archaeological and Paleontological Center, a diminutive jawbone fossil has emerged as part of the oldest fur seal on record.

The remains of the species Eotaria cypta were first discovered within a Southern Californian rock formation in the 1980s, but misidentified as an ancient walrus. It wasn’t until the University of Otago’s PhD student Robert Boessenecker took a closer look at the fossil’s teeth that a five-million-year evolutionary gap was filled for the fur seal.

“Until now we had no fossil evidence for the first five million years of fur seal and sea lion evolution,” said Boessenecker in the University’s press release. “It’s extremely satisfying to have remedied that.”

Based on the age of the rock formation, researchers estimate that the creature roamed the seas about fifteen-to-seventeen million years ago. The family of Otariidae, which includes fur seals and sea lions, previously only dated back ten-to-twelve million years.

“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,” adds Boessenecker.

The rarity of Eotaria cypta fossils remains an enigma, but paleontologist Dr. Naoki Kohno suggests that the majority of them have settled into the depths of the open ocean. It’s possible that these old bones are simply inaccessible by the nature of the creature’s natural habitat.

Boessenecker agrees that “This hypothesis is supported by this fossil having been collected from rock formed by sediments deposited in what was then continental shelf, rather than extensively studied inland fossil sites, such as Sharktooth Hill, that formed in bays.”

Eotaria, the genus name of the animal, appropriately stands for “dawn sea lion.”

The findings were originally published in the journal Biology Letters.