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Re: possible ceratopsian feeding behaviour?
Stephan Pickering (firstname.lastname@example.org) 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.
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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