Re: Platyhystrix and dinosaur humps/sails

["Jaime A. Headden" <qilongia@yahoo.com>]

  My piece on humps vs. sails:

  I'm not going to reiterate this thread too far, and
advise those out there wondering this as well that
this subject has been covered extensively on the
archives, and I do believe *Platyhystrix*, the flat
porcupine, has been mentioned before. However, flat
bladelike neural spines are not found in the "humps"
of extant animals, these being primarily found in
bovids; broad distal expansions of the dorsal and
cervical neural spines support and anchor various
units of the nuchal and supraspinal ligamentation and
some muscle groups (e.g., m spinalis cervicis, etc.).
But these are reduced in known dinosaurian neural
spines of the anterior dorsal and cervical region
except for some sauropods.

  Iguanodontians (esp. *Ouranosaurus*) exhibit some
interesting neural spine morphology of this region
that I am most interested in examining in more detail,
but needless to say is very reduced relative to
theropods, and would not have supported a muscular or
fleshy "hump" but may have allowed thickened nuchal
ligaments, fats, and laminate tissue that would have
given the dorsocervical region a thicker, higher
profile than commonly reconstructed.

  This is in contradiction to the "humps" of bovids
which, except for some Bovini, are merely composed of
the shoulder and caudal cervical musculature and fatty
deposits, present all over the body. The humps
*Camelus* do not conform to osteological neural
spines, but instead are structural fatty and laminate
tissue, and should not be considered comparative to
any dinosaur form in the abscence of knowledge of
soft-tissue anatomy of fossils.

  *Platyhystrix*, as an amphibian, was cold-blooded
and may have used the sail much as has been proposed
for *Dimetrodon* and edaphosaurids, as a
thermoregulatory device, to raise the mean body
temperature, but this would actually increase body
water loss in the amphibians (but purportedly not the
synapsids (Carroll, 1988)), and that would not be so
pleasureable, I think. Alternatively, stegosaurians,
*Ouranosaurus*, and *Spinosaurus* appear to exhibit
more regulated thermophysiology than amphibians, and
would not have suffered water loss as much as
*Platyhystrix.* They would in fact have benefited more
probably from increased body temperature during cold
periods, but this subject is nowhere near closed. The
debate rages on.

  Anyway, that's my piece on the h-vs.-s,


=====
Jaime "James" A. Headden

"Come the path that leads us to our fortune."

Qilong---is temporarily out of service.
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