RE: Guts-Eating Spinosaurs

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

Jura (archosaur@reptilis.net) wrote:

<<The skull in at least Suchomimus is very narrow, as is the lower jaw of
the holotype of Spinosaurus aegyptacus. When something is narrow, it is
easily breakable and when you are dealing with struggling fish with it's
body moving all around, the tail could snap the skull. Baryonyx was a
relatively basal creature, so it is logical it is more sturdy in the jaw
area, but the Spinosaurus maroccanus had a very slender jaw. Taken to the
extreme in the 7ft skull. Bye the way, does anyone have a picture of this
skull that I could possibly have?>>

and Tracy Ford (dino.hunter@home.com) replied:

<Yes, Spinosaurids skulls are narrow, but narrowness of the skull doesn't
equate to weak. Lots, if not the majority of theropod skulls are narrow.
Monolophosaurus is very narrow, Dilophosaurus is narrow, etc. Spinosaurids
have very thick front jaws and are very strong, maybe used in a pincer
like motion because that is where the thickest, largest teeth are.>

  Tracy Ford is correct in this.

  Though generally the spinosaurid jaw, using *Suchomimus* as the most
complete example from which to draw from, is narrow, this is compared only
to linear measurements. The width the upper jaw is nearly equal to it's
depth, pretty much D-shaped or triangular in section rostral to caudal
towards the orbits, where the skull becomes trapezoidal, wider at the
bottom than the top. The equal width to depth and the triangular section
of the skull suggests that the skull could resist a good deal of ventral
or lateral bending, and the extent of the palate caudally under the
antorbital fenestrae shows extensive reinforcing. It's very difficult to
bend a triangular set of spars. Go on, try it. The lower jaw was also
practically as wide or wider than it was deep along it's length, paired to
the halves of the rami, roughly quadrate in section to rectangular
caudally. Rostrally at the tip, it was triangular.

  As the jaws progress caudally, the rami spread apart, and thus the
cross-section changes. But the rami themselves become deeper, compensating
for the shift in jaw stress rostrally. The best stress-reducing region of
the jaw is the very front of the snout, rostral to the external nares,
which is laterally expanded into the "spoon-shaped" premaxillae,
compensatory dentaries rostrally, and the terminal rosette of teeth. A
similar arrangement can be seen in criorhynchid pterosaurs, though they
have crests and fused symphyses that change the structure somewhat.

  Spinosaur jaws, upon inspection, do not appear to be very weak at all,
and were perfect for seizing with at the very front. Comparatively, this
is seen otherwise only in aquatic archosaurs such as crocodyliforms
(pholidosaurs and gavials, as well as some narrower-snouted crocodylids)
and pterosaurs, which have been almost universally assumed to be
piscivorous, largely based on anatomy, though admittedly also somewhat on 
paleogeography.

=====
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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