Bizarre Cast of Marine Mammals Revealed in 8-Year California Fossil Excavation

A study of hundreds of fossilized bones and teeth excavated from the Purisima Formation on the Northern California coast reveals an odd and eclectic community of pre-Ice Age marine mammals.

The cast of characters included strange double-toothed walruses, dwarf baleen whales, porpoises with overbites and a species of river dolphin that's closely related to a now-extinct river dolphin species from China.

In all, a total of 21 marine mammal species were documented in the Purisima Formation fossil record, which dates between 5 million and 2.5 million years old.

Additionally, a never-before-scene species of whale that's related to blue whales and fin whales - the largest living mammals - was in the fossils. The new whale species, which was named Balaenoptera bertae, would have been between 5-6 meters long, about the size of today's minke whale.

The fossil collection represents eight years of excavation and research by Robert Boessenecker, of New Zealand's University of Otago.

The fossil site, which is located along Half Moon Bay in the San Francisco Bay area, contains evidence of an array of creatures and paints a picture of what ocean life would have been like millions of years ago.

"The mix of marine mammals I ended up uncovering was almost completely different to that found in the North Pacific today, and to anywhere else at that time," Boessenecker said.

Primitive species of porpoise and baleen whales were living alongside comparatively modern marine mammals such as fur seals and right whales, and species that are not far geographically removed were at one time living nearby, Boessenecker learned from the fossil record, which be began studying at age 18.

"At the same time as this eclectic mix of ancient and modern-type marine mammals was living together, the marine mammal fauna in the North Atlantic and Southern Ocean were already in the forms we find today," he said.

Boessenecker attributed the strange mix of marine mammals to the Bering Strait still being closed at the time and the formation of the Isthmus of the Panama, which 2 million years ago, was a new geological feature.

"Once the Bering Strait opened and the equatorial Pacific cooled during the Ice Age, modernized marine mammals were able to migrate from other ocean basins into the North Pacific, leading to the mix we see today," Boessenecker said.

A research paper detailing Boessenecker's work is published in the journal Geodiversitas.