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Re: SUCKING WALRUSES

Nick L wrote...

  Both sea otters and walruses have massive crushing teeth to
 deal with molluscs


Walruses do not use their teeth to crush prey, as was once thought -
they are suction feeders that cruise head-down along the seabed and
suck off the protruding soft parts of bivalves. Wear on the teeth is
apparently generated by sand grains which are sucked in with the prey.
This foraging method explains the characteristic wear on walrus tusks
(the leading edge of the distal end is always polished smooth) and also
the strongly vaulted palate and phenomenal throat musculture. A
sucking walrus can generate 1 negative atmosphere and specimens in
captivity have removed the heavy metal plugs from the bottoms of
their swimming pools.

For references see King's _Seals of the World_ and also de Muizon's
work on _Odobenocetops_, a walrus-mimicking odontocete whale.

Hadn't heard this previously. It seems to me, though, that this can't explain the morphology of the walrus skull. The proximal ends of the dentaries are thicker than my wrist and the bones then about double in size towards the symphysis- where they are tightly fused together. One could easily crack walnuts open with the bone just by pounding on them a single time. Plus, the adductor musculature is expanded over the entire top of the skull and there's even a small "frill" around the back of the temporal area where the temporalis presumably went, and the zygomatic arch, where the masseter attaches, is plenty strong to boot. If they were solely using suction power to feed, we'd expect something more along the lines of a matamata turtle or a flounder, not a nutcracker. Furthermore, the teeth exhibit distinct wear facets (upper teeth exhibit a lateral wear facet where they rub against the lower teeth and a medial wear facet from wear from something else; lower teeth exhibit a single wear facet), not a more rounded, allover wear appearance that you'd expect if they were simply subjected to sandblasting. I can buy that walruses often do not crush their food, but I'm not sure I'm convinced that they never crush their food. I'm curious, tho. What's the evidence/rationale behind the inference that the jaws aren't used?