Re: Spinosaurus sail

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

Waylon Rowley (whte_rbt_obj@yahoo.com) wrote:

<The skull of Baryonyx has fused internasal sutures, and the
maxilla and premaxilla interdigitate tightly. 1 synapomorphy of
the Spinosauridae is "fused interpremaxillary suture at
maturity", but if we lack fully adult specimens, it makes you
wonder where they come up with this conclusion. Baryonyx also
has an interlocking "peg-in-notch" scapulocoracoid union. As for
the rest of the skeleton, I have no idea. I need the papers for
both Suchomimus and Baryonyx (and any other spinosaurs except
Spinosaurus, for that matter!), but it certainly seems to me
that these animals, if not fully mature, were at least
approaching adulthood.>

  Most spinosaurid premaxillae are fused. It is apparent that
this is a mechanical condition, for resisting torsion of the
premaxillary halves during predation (the spoon-shaped
premaxillae then serve a dynamic function that concentrates
resistance at the tip, between elements). The fusion apparently
occurs caudorostrally (i.e., back to front) as less mature
premaxillae (*Baryonyx*, paratype of *Cristatusaurus*) have a
slight suture evidence at the tip of the elements, and some
(*Suchomimus* and *Irritator*) have fully fused premaxillae,
whereas others (type of *Cristatusaurus*) have completely
unfused premaxillary halves, but are smaller than the
nearly-fused elements. Not having the several known *Suchomimus*
premaxillae to observe aside from the type, I make the following
observation on limited data: premaxillary fusion occurs fairly
early in ontogeny, as a dietary aid, instead of an indicator of
maturity; as an animal approaches a certain size, the shape of
the muzzle employs some restraint on the way in which food can
be acquired, and the animal changes its diet to compensate, as
it gets older. The premaxillae become more hooked in profile in
maturity, and the rostralmost teeth larger and longer.

=====
Jaime A. Headden

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

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