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Re: Scarey spinosaurs and super creeps



Cliff,

  I think the similarities between the snout of coelophysoids and spinosaurids,
widely advanced by GSP in _Predatory Dinosaurs of the World_. This was largely
based on the "kink snout". The problem is that the "kink" between the snouts is
arrived at in two different ways:

  In coelophysoids, the gap is acheived by rostral clusturing of the teeth in
the anterior dentigerous margin of the premaxilla, and thus "pushing" the
posterior premaxilla above the maxilla.

  In spinosaurids, however, the snout is acheived by narrowing of the posterior
premaxilla with expansion of the medial premaxilla posteriorly and ventrally,
and the protraction of the premaxilla anterior to the vomers so that, even by
the position of the external nares, the vomer is restricted from the anterior
snout. This also makes a lateral embayment that would allow the rostral dentary
teeth to close lateral to the premaxilla itself, not inset, though this
conclusion, illustrated in Dal Sasso et al., is based on unarticulated cranial
fragements. Jaws of *Suchomimus* and *Barynonyx* are not complete enough to
provide am articulation to test the theory by.

  Studies by Rauhut, Holtz, and Allain show that posctranially and even in the
braincase, spinosaurids are both much more derived relative to birds than are
coelophysoids like *Dilophosaurus*, and that they seem to group with
megalosaurids, such that the snout "kink" is convergent, aside from the
morphological dissimilarities between the two designs.

  But the similarities may indicate similar diet. Hopefully, Rayfield or others
will get around to studying *Dilophosaurus* and a more or less complete
spinosaurid skull to determine their mitigation and resistance to force, and
help imply a function.

  I hope this helps,

  Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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