A previously thought Walrus fossil has been instead found to be the remains of the oldest ever known fur seal. This mistaken ‘Walrus’ species was tiny, with the sizes of the species’ adults, not growing beyond the size of a contemporary sea otter. The fur seal, according to estimates based upon the fossilized partial jaw in possession, may have been around the size of a juvenile New Zealand fur seal.
A doctoral student in geology, Robert Boessenecker of the University of Otago, New Zeland came upon this species, while he was searching among fossil collections kept at the California Paleontological Center. He came across the fossilized remains of a jaw belonging to a previously thought of ‘walrus’ species, but he recognized right away that the remains belonged instead to the oldest known fur seal species.
Boessenecker and his colleague Morgan Churchil, from the University of Wyoming have decided to name this new genus and species of fur seal as ‘Eotaria Crypta’. The word, ‘Eotaria’ means dawn sea lion, thus acknowledging this species as the dawn of the fur seal in the evolutionary history of life on Earth. This accidental discovery also benefited evolutionary scientists by filling in a ‘ghost lineage’ of the fur seal. Ghost lineages are those periods of Earth’s history which have not thrown up any evolutionary linkages between past and later evolved species. This was important as far as fur seals and sea lions are concerned, because there exists a very limited fossil record for both. The available records dated back only to 10-12 million years ago.
“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.”
This was perplexing for evolutionary scientists because the fur seal’s closest known relative, the ‘Walrus’ could trace its evolutionary history back to 16-17 million years ago. Thus a gap of 5 million years existed as a ‘ghost lineage’ in the evolutionary chain of the fur seal. This gap between logical consistency and observable fact has now been filled with the discovery of the oldest known fur seal, which has pushed back the available record of fur seals to 16-17 million years ago.
This discovery not only filled up the evolutionary gaps for scientists, but also completed a transitional link between the complex bear like teeth of the earliest pinnipeds and the simplified and structured teeth of the modern sea lions. The fur seal’s intermediate quality of teeth arrangement sits prettily between the available observations on the evolution of the family, ‘Otariidae’.