Fossils Reveal Eclectic Ancient Marine Mammals Of North Pacific
February 6, 2014

Fossils Reveal Eclectic Ancient Marine Mammals Of North Pacific

redOrbit Staff & Wire Reports - Your Universe Online

The pre-Ice Age marine mammals of the North Pacific were a diverse and fascinating lot, according to an analysis of hundreds of fossil bones and teeth excavated from the San Francisco Bay Area's Purisima Formation.

Robert Boessenecker, a geology PhD student at New Zealand's University of Otago, put together a record of 21 marine mammal species that were fossilized 5 to 2.5 million years ago, including dwarf baleen whales, odd double-tusked walruses, porpoises with severe underbites and a dolphin closely related to the now-extinct Chinese river dolphin.

Among the findings was a new species of fossil whale, dubbed Balaenoptera bertae, a close relative of minke, fin, and blue whales.

Boessenecker named the whale in honor of San Diego State University's Professor Annalisa Berta, who has made numerous contributions to the study of fossil marine mammals and has mentored many students.

Although an extinct species, the Balaenoptera lineage has lasted for three to four million years.

B. bertae would have been approximately 15 to 20 feet in length, slightly smaller than modern minke whales, Boessenecker said.

The analysis is the result of several years of research for Boessenecker, who began the study in 2004 at the age of 18 after being tipped off by a local surfer about bones near Half Moon Bay. When he discovered the fossil site, he was astonished by the numerous bone-beds and hundreds of bones sticking out of the cliffs.

Boessenecker excavated the incomplete skull of B. bertae during early field research in in 2005. The fossil was encased in a hard concretion that took five years to remove.

"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," he said.

Primitive porpoises and baleen whales were living side-by-side with comparatively modern marine mammals such as the Northern fur seal and right whales. And species far geographically and climatically removed from their modern relatives were also observed, such as beluga-like whales and tusked walruses, which today live in the Arctic.

"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,” Boessenecker said.

This bizarre fauna existed until as recently as one to two million years ago, he added.

Its eccentricity was likely maintained by warm equatorial waters and barriers to migration by other marine mammals posed by the newly formed Isthmus of Panama, and the still-closed Bering Strait.

"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.

The findings appear in the most recent edition of the international journal Geodiversitas.