You are not permitted to download, save or email this image. Visit image gallery to purchase the image.
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.