Four-Tusked Walrus, New Whale and 19 Other Fossil Mammals Discovered at California Surf Spot

Balaenoptera bertae

Ten years after a surfer first tipped him off to some bones eroding out of a sandy bank, a paleontologist says he has uncovered a massive cache of marine mammal fossils in the Bay Area, some of which appear to be new to science.

Excavated at Half Moon Bay, a choice surf spot about a half-hour drive south of San Francisco, the deposit includes fossil evidence of a new species of whale, a walrus with four tusks, a relative of the recently extinct Chinese river dolphin, and a porpoise that appeared to have a “serious underbite.”

Balaenoptera bertae
An artist’s rendering of Balaenoptera bertae, a newly discovered species of baleen whale from a fossil deposit in Northern California. (Artwork by RW Boessenecker)

“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,” said Robert Boessenecker, a Ph.D. candidate in Geology at New Zealand’s University of Otago, in a statement.

Among the hundreds of fossil bones and teeth, the clearest picture to emerge so far is that of a diminutive species of baleen whale that, at about 5 meters long, was slightly smaller than today’s minke whales.

The newly identified whale, given the name Balaenoptera bertae, lived more than 3 million years ago, Boessenecker said, with other fossils in the cache dating back as much as 5 million years.

Boessenecker describes the new species in the latest issue of the journal Geodiversitas, along with details of his other findings, such as a fossil walrus from the genus Dusignathus, which grew four short tusks — two coming down from the top row of teeth and two erupting upward from the jaw.

There’s also evidence of other mammals with “strange adaptations,” he writes, like a still-unnamed porpoise whose lower jaw extended far beyond the upper, giving it a rather excessive underbite.

Also among the remains are fur seals, a pilot whale, two species of dwarf baleen whales, and two right whales, he says.

This fossil menagerie suggests that, in the pre-Ice Age North Pacific, early species of marine mammals lived alongside more derived species that have persisted into the present day. [Read about another fossil marine species recently found in California: “Fossil of Huge Aquatic Mammal, a ‘New Paradox,’ Discovered in Southern California“]

“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.

As the climate changed and land masses shifted, he explained, new migratory paths opened that allowed marine mammals to disperse, and the profile of life in the North Pacific to change.

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

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Robert W. Boessenecker (2013). A new marine vertebrate assemblage from the Late Neogene Purisima Formation in Central California, part II: Pinnipeds and Cetaceans Geodiversitas DOI: 10.5252/g2013n4a5

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  1. Zirconia Wolf

    Are there ANY pictures of the four-tusked walrus skull available ANYWHERE on the web???? I have just spend the last hour going in circles (which all come back here) trying to find so much as a simple artist’s rendering of this “great discovery” but have come up completely empty. Why is it so hard to post even a simple cellphone picture of what sounds like such an amazing find? Very frustrating!