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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, 

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"