New research throws doubt on earlier 'killer walrus' claims
Palaeontologists who examined a new fossil found in southern
California have thrown doubt on earlier claims that a "killer walrus"
once existed. A University of Otago geology PhD student Robert Boessenecker and
co-author Morgan Churchill from the University of Wyoming have just published
their paper about the fossil in the online scientific journal PLOS One.
The paper reports that the new fossil-find, of the extinct walrusPelagiarctos from southern California, prompts a
different hypothesis to an earlier one that a "killer walrus"
existed, preying on other marine mammals and/or birds.
Fossils of the walrus were originally found in the 1980s. The
large, robust size of the jaw bone, along with the sharp pointed cusps of the
teeth similar to modern bone-cracking carnivores like hyenas, suggested thatPelagiarctos fed upon other marine mammals rather than
the typical diet of fish as in modern walruses.
However the new fossil, a lower jaw with teeth, and more
complete than the original fossil, suggests to the Otago and Wyoming
palaeontologists that the Pelagiarctos was
more of a fish eater as it lacked adaptations for being a "killer
walrus."
The
evidence pointed to the tooth shape being unlikely to have been adapted for
feeding upon large prey; instead it was an example of primitively retained
tooth shape.
"This
new find indicates that this enigmatic walrus would have appeared similar in
life to modern sea lions, with a deep snout and large canines," says Mr
Boessenecker.
The researchers estimated Pelagiarctos to be
similar in size to some modern male sea lions (about 350 kg or 770 lbs).
"However, modern pinnipeds (seals, sea lions, and walruses)
of small and large body sizes are dietary generalists, and tend to have diets
rich in fish -- including sea lions similar in body size to Pelagiarctos, which means that its large
body size alone doesn't make Pelagiarctos an apex predator."
The new study also analysed the evolutionary relationships of Pelagiarctosfor the first time, and found
it to be an early sea lion-like walrus that was most closely related to another
sea lion-like walrus, Imagotaria downsi, also
from California.
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.
Source: University of Otago
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Posted by Unknown
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