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IMPLICATIONS OF TOOTH WEAR
Sauropod teeth are often heavily worn. This is one indication that
they were _not_ grabbing mouthfuls of soft, aquatic vegetation. Also,
when feeding at ground level, or on aquatic plants, animals
supposedly ingest bits of grit and dust which leave microscopic scars
on the teeth. Tony Fiorillo determined that the absence of these on
diplodocid teeth suggested that they fed on vegetation growing well
away from the ground. We should keep this mind when discussing
behaviours and ecologies in possibly 'stiff-necked' sauropods.
BTW, in palaeomammalogy, examination of wear facets often provides a
possible last word on an ecology that simply cannot be determined by
simply morphological gestalt, as shown by numerous papers on ungulate
tooth microwear by Nicholas Solounias and Christine Janis. The
bizarre protoceratids, for example ('pecoran-mimicing tylopods'),
might have fed on soft, aquatic vegetation: however, their deer- or
antelope-like body form would suggest that they were
mid-height browsers. As those who study armadillos have said,
"ANATOMY IS NOT DESTINY".
Diplodocid teeth are often heavily worn at their tips, with a
well-developed, polished oblique wear facet. The really strange thing
is the orientation of these facets: they face OUTWARDS rather than
inwards. The only way to explain this pattern of wear on both upper
and lower teeth is to have the animals grabbing foliage, and then
either pulling it by bringing the head downwards (creating the wear
facets on the upper teeth as the vegetation wears against the outer
surface of the upper dentition) or upwards (creating wear facets on
the lower teeth as the vegetation wears against the outer surface of
the lower dentition). This is exactly the model proposed by Pauls
Barrett and Upchurch in their _Gaia_ paper on sauropod feeding
mechanisms. I feel this model is consistent with what people are
saying about neck mobility as all of this can happen with a
relatively immobile, horizontal neck, *or* in a tripodal rearing
stance. Diplodocids may also have been especially good at shearing
vegetation off without too much neck motion for, as Barrett and
Upchurch propose, they may have had propaliny: the ability to move
the jaw backwards and forwards by way of a sliding jaw articulation.
BTW, the oblique wear facets on the teeth of these animals is
another argument against their having a trunk-type proboscis or
mobile upper lip. The function of such a structure would
presumably be to assist the stuffing of food into the mouth. This
behaviour would not be consistent with the pattern of tooth wear.
Jaime Headden said...
> *Antarctosaurus wichmanianus* had a very squared off
> jaw, and perhaps perfectly exapted to graze with, as
> is seen in grazing animals like the black rhinoceros
> as opposed to the white rhinoceros, whose snout is
> more pointed.
You have it the wrong way round, Jaime: it is the grazing white rhino
(_Ceratotherium_) which has the squared lips, and the browsing black
rhino (_Diceros_) which has the pointed, prehensile upper lip.
"They wait for me in the forest"