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Re: possible ceratopsian feeding behaviour?



REPLY:
The work of Lull, Forster, Tim Rowe, Larry Witmer,
Scott Sampson, et al., on ceratopsian facial anatomy
indicates masticatory habits were, as you note,
shearing. However,I tend to think they were grazers,
and, as well, that field observations of feeding of
rhinos just might provide one with inferences re: late
Cretaceous ceratopsians in environmentally stressed
regions. Granted that rhinos lack rostrally tapering
beaks, and their locomotion is not comparable to
ceratopsians (I have yet to see convincing
biomechanical evidence ceratopsians could gallop, as
Dawn Adams's excellent dissertation on ceratopsian
locomotor biomechanics disproves the assertion for
most of the larger taxa), it remains possible both
share analogous ecomorpological constraints.
*******************************************************
--- "Jaime A. Headden" <qilongia@yahoo.com> wrote:
> Stephan Pickering (stefanpickering2002@yahoo.com)
> wrote:
> 
>   Regarding ceratopsian mouth shape: ceratopsians
> have a triangular beak
> in both transverse and longitudinal section. In
> fact, taking the shape
> into 3D, it is rougly a pentahedral pyramid; this
> differs from the
> rhinocerine cubic snout, but only a little. The
> masticatory section of the
> ceratopsian jaw is very long and narrow, but deep,
> with impressive anchors
> for the jaw closing muscles (namely, a medial flange
> for the pterygoideus,
> a foreward, wide anchor for the psuedotemporal, and
> a fairly narrow and
> long adductor mandibulae complex that formed a
> perfect cross-action to the
> pseudotemporal and would have perfected the
> scissor-like occlusion seen in
> the teeth; these, in fact, show that theogosis was
> shearing, rather unlike
> modern mammals of any type except the carnassials of
> some advanced
> carnivores (tylacoleonids, nearly all ailuriforms,
> and most non-ursoid
> caniforms, etc.). The beak was also tapered at
> front, and the apparatus
> was with fitted, parrot-like "pincers" in front
> coupled with rear-ward
> flattened, everted platforms. The last can be
> described as follows:
> 
>   The rear half of the predentary forms a broad V on
> its external surface,
> but a narrower V internally; this shows that the
> dorsal margins of the
> rear beak broaden towards the end, and the dorsal
> surface is turned so
> that it forms a flattened platform that faces
> dorsolaterally, and a
> distinct crest can be follow from the midheight of
> the predentary on the
> side to the tapered tip. This morphology is coupled
> with the
> rostropremaxillary unit, which is blade-like
> (tomial) in the rostral part
> and becomes broader and rounded to flat towards the
> rear and ventral to
> the external narial fossa (the big, non-confluent
> nasal aperture, which
> Witmer and Sampson should be getting around to
> publishing soon on -- very
> nice anatomy), and occluded the laterally everted
> portion of the
> predentary. Surprisingly, the keratinous beak should
> noticeably shape the
> shape, but this is conceived as being of little
> consequence given the
> conformity of bony beak shape and their approximate
> fit to one another.
> 
>   Such anatomy disregards the concept of grazing
> altogether, which effects
> rhino diet and facial anatomy more than it has
> ceratopsians. Instead,
> narrow snouts versus broad in artiodactyl and
> perissodactyl evolution
> seems to favor a browsing anatomy, and the beak
> would have provided some
> curious constraints and advantages.
> 
>   Not sure about wet versus dry seasons, I think the
> jury is still out on
> this; Eberth and Jerzyciewicz regularly work the
> badlands of Alberta, and
> the data seems to suggests that even when "dry",
> most ceratopsians were in
> a fairly humid, warm environment not unlike that of
> temperate wetland
> forests and marginal (brakish) and mangrove swamps.
> 
>   Cheers,
> 
> =====
> Jaime A. Headden
> 
>   Little steps are often the hardest to take.  We
> are too used to making leaps in the face of
> adversity, that a simple skip is so hard to do.  We
> should all learn to walk soft, walk small, see the
> world around us rather than zoom by it.
> 
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