A postdoctoral student in New Zealand has discovered the oldest fur seal fossil known. This could be the missing link to fill the 5-million-year gap in the evolutionary history of sea lions and fur seals.
Robert Boessenecker, a Ph.D. student at the University of Otago, and Morgan Churchill from the University of Wyoming found the fossil while going through the fossil collection at the John D. Cooper Archaeological and Paleontological Center in California. Boessenecker said that they could instantly tell that the fossil belonged to an ancient 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. 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," said Boessenecker.
In paleontology, such a gap is referred to as "ghost lineage," which the latest discovery has eliminated. The researchers believe that no other fossil confirmation is in record for the initial 5 million years of sea lion or fur seal evolution.
The fossil was discovered a few decades ago, but it was misidentified as the remains of a small walrus species. Boessenecker said that the fossilized part of the jaw, which has some well-conserved teeth, was actually recovered at a Southern California rock formation that dates back to about 15 million to 17 million years.
However, the latest discovery suggests that the fossil belongs to a tiny fur seal, which may have been similar in size to a juvenile New Zealand or southern fur seal and slightly bigger than a sea otter.
The researchers have named the new species of the fur seal Eotaria crypta. The researchers also say that it is still a mystery that only one fossil of the early seal exists on record because fossil excavations at similar rock formations in California have been very extensive.
The study was published in the journal Biology Letters.
