'Killer' walrus? O.C. fossil raises doubt
Was this a 'killer walrus?' New research says an earlier suggestion that this 15-million-year-old species hunted other sea mammals might be incorrect. Rendering shows position of jawbone found in Orange County.
ROBERT W. BOESSENECKER, UNIVERSITY OF OTAGO
The frightening picture seems drawn for science fiction: a predatory, "killer" walrus with the tastes of a great white shark, patrolling the California coastline millions of years ago.
Now a fossil found in Orange County and a scientist in New Zealand are casting doubt on whether such a creature existed at all.
A jawbone at least 15 million years old, found in 1997 during construction in Mission Viejo, is revealing new details about an early and extremely rare type of walrus known as Pelagiarctos, geology PhD candidate Robert W. Boessenecker says in a newly published study.
And those features do not add up to an "apex predator" – a species such as a great white shark or a mountain lion that sits at the top of its food chain.
"We can't rule it out, but our findings basically say that there's no evidence it was adapted or specialized for eating warm-blooded prey," Boessenecker, a California native who conducts his research from the University of Otago, in Dunedin, New Zealand, wrote in an email.
The "killer walrus" idea was first put forth by scientists in the 1980s after the discovery of a similar fossil near Bakersfield.
The animal's large teeth, imposing size and even its rarity all argued in favor of a hunter of other sea mammals such as seals and sea lions.
These early walruses did not possess the long, downward-pointing tusks of today's more familiar variety. They looked more like sea lions themselves.
And the Orange County version has some minor differences from the original specimen, so while it is classed as a close relative, it does not appear to be the same species.
Still, it is close enough, Boessenecker said, to allow testing of the killer walrus hypothesis.
His and his fellow researchers' tests might be enough to banish the killer walrus to the realm of science fiction.
They used a careful plotting of some 90 characteristics of pinnipeds – seals, sea lions, walruses and their relatives – to place the Orange County specimen in context with the many species that came and went over millions of years of evolution.
They found that the O.C. walrus's teeth, for example, were significantly larger than those of earlier walruses, but otherwise showed no differences. The scientists did not find that the teeth were especially sharp, another point that could have bolstered the killer-walrus case.
The larger tooth size, Boessenecker said, is likely a characteristic retained by this species from more primitive ancestors – not a new adaptation for catching larger prey.
And while it was a good-sized animal, about as big as a modern California sea lion, that doesn't help the "killer" hypothesis, either. Big seals, sea lions and walruses today are mostly general feeders, not hunters of large, warm-blooded prey.
Rarity also can be a sign of a predatory animal; there are always far fewer of them compared with their prey. But this early walrus's rarity could mean simply that it was uncommon in the region, wandering in only occasionally from more densely populated areas.
The new findings, published in the research journal, PLOS One, don't kill off the killer walrus definitively, Boessenecker says.
But they do suggest a somewhat tamer lifestyle for Pelagiarctos, one that involved eating fish, and perhaps itself serving as prey for something else.
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