Killer walrus theory undone

University of Otago PhD student Robert Boessenecker holds a modern New Zealand fur seal skull and an artist's impression he has created, showing an ancient, and now extinct, walrus species. Photo by Peter McIntosh.

Robert Boessenecker may have just helped dispose of a myth involving a prehistoric killer.

He believes that a mysterious and now extinct sea creature which was once swimming off the coast of what is now modern California more than 15 million years ago may not have been a ''killer walrus'' after all, despite earlier claims.

Mr Boessenecker, who hails from California and these days is a University of Otago geology PhD student, has examined a ''new'' fossil found in Southern California and thrown doubt on earlier claims that a ''killer walrus'' once existed.

Mr Boessenecker and co-author Morgan Churchill, of the University of Wyoming, in the United States, undertook the research, which was published in the online scientific journal PLOS One. The new fossil-find, of the extinct walrus Pelagiarctos, prompted a hypothesis different from an earlier one that a ''killer walrus'' existed, preying on other sizeable marine mammals and/or birds.

The large, robust size of the initially-found jaw bone, and the sharp pointed cusps of the teeth - similar to modern bone-cracking carnivores such as hyenas - initially suggested that Pelagiarctos fed upon other marine mammals. But the new fossil, a lower jaw with teeth, and more complete than the original fossil, suggested to Mr Boessenecker and his colleague that the Pelagiarctos was more of a fish eater, lacking adaptations for being a ''killer walrus''.

The new find indicated this ''enigmatic walrus'' would have appeared similar in life to modern sea lions, ''with a deep snout and large canines'', and of similar size to some modern male sea lions (about 350kg). Mr Boessenecker noted that modern pinnipeds - seals, sea lions and walruses - whether of small and large body sizes, were ''dietary generalists'', tending to have diets rich in fish.

The study was supported by a University of Otago Doctoral Scholarship, and grants from the Geological Society of America, The Palaeontological Society, and a National Science Foundation EAPSI Fellowship.

- john.gibb@odt.co.nz