Re: The Hunchback of the Mid-Cretaceous

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

Mickey Mortimer (mickey_mortimer11@msn.com) wrote:

<Bailey, Jack Bowman, 1997, Neural spine elongation in
dinosaurs: sailbacks or buffalo-backs?: Journal of Paleontology,
v. 71, no. 6, p. 1124-1146.>

  I would personally like to see this reference, but sad to say
I've not had much luck :)

  Suffice it to say, the very arangement of the spines, the lack
of any distal expansion or areas for tendonous attachment
besides the cranial and caudal sulci on the neural spines
themselves (between the paired pre- and post- spinozygapophyseal
laminae), suggesting the lack of a good deal of muscular support
there. The back was probably quite rigid, in that the vertebrae
are midly opisthocoelous to platycoelous, which restricts motion
to some degree.

  Whether the spines supported a fatty deposit is not answerable
by vertebrate paleontology ... however, a withers reconstruction
is implausible given the form of the spines compared to extant
"humped" animals which have robust, wide, and distally expanded
spines and strong positions for attachement of tendons and
muscles. *Acrocanthosaurus* is similar in having thicker spines
than *Spinosaurus*, but the spines are not expanded
transversely, and the spine would have been as laterally rigid
if not more so by the amphiplatyan to platycoelous dorsals.

  Of the known theropods with expanded dorsal spines, they can
be grouped into possibly two categories, both incomparable to
either sphenacodonts like *Dimetrodon* or modern bovids:
*Spinosaurus* has extraordinarily thin and slender spines, and
the hieght is quite impressive in the size of the animal; the
spines tend to taper distally, and are curved forward or back,
and inclined, unlike withers or sphenacodonts, but like other
theropods. In *Becklespinax* and *Acrocanthosaurus* the verts
are expanded distally only craniocaudally, with some
mediolateral distal expansion, and the spines are covered with
more complex laminae and ridges, supporting the idea that they
were supporting massive musculature. It is unlikely that Acro
had fatty deposits, neccessarily, as the spines are embedded in
muscular flesh; but not so in *spinosaurus*; the other
spinosaurids, like *Baryonyx*, have slender, expanded but then
tapered neural spines, with *Suchomimus* having only distally
craniocaudal expansion.... So it would seem that *Spinosaurus*
may have had a true sail.

  Hadrosaurs typically have expanded neural spines
mediolaterally, though not very robustly expanded, most
characterized by the club-shaped caudal and sacral spines in
*Bactrosaurus* and *Barsboldia*; the iguanondots have narrow
spines but inflexible spines, and they were also robustly
covered with muscle-supporting laminae and ossified tendinous
rods. An exception seems to be *Ouranosaurus* and it's strongly
expanded verts, which have a form similar to *Spinosaurus* and
having mildly tapering distally, and no mediolateral expansion.

  Few sauropods have especially elongated neural spines,
dicraeosaurids being the best example ... *Amargasaurus* has
cervical neural spines that are both ovate, circular, and
plate-like in section. the mid-cervical spines are the most
platelike, and these become more complex with spinodiapophyseal
lamina in the shorter anterior dorsal spines, and would have
supported much flesh and meat, over-ruling the extent of a sail
to the neck alone, and probably only in the cranial 9/10's of
the neck from the material I've seen. The cervicals also seem to
be immobile for the most part the the base of the neck, based on
the short verts and the close inclination and near-contacts of
the spines. They are only broad from one another in the anterior
5/7's of the neck....

  It would be unwise, in my opinion, to shoe-horn theropods and
other tall-spined dinosaurs into the idea of a bovine vs.
pelycosaur debate. That the sail-like form of the verts in some
animals, like sphenacodonts or *Paleohystrix*, compare to some
dinosaurs, or not at all, as in the theropods I list, makes them
incomparable. A new concept based on the functional anatomy and
actually reconstructing the soft-anatomy from the bones
themselves and not how to interpret them from other living
animals, should be done _first_, and then compared to modern
animals.



=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

__________________________________________________
Do You Yahoo!?
Get personalized email addresses from Yahoo! Mail
http://personal.mail.yahoo.com/