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Re: Spinosaurs as what?
Renato Santos wrote:
*Spinosaurus* has as far as we know piscivorous adaptations; I'm just
proposing a modus operandi for the creature's feeding habits based on
extant creatures that approximate its niche (if there are any). In fact,
*Spinosaurus* might as well had brightly colored feet as some herons do to
scare off fish as it waded ;-)
Before you go too much further with this, I would caution that not everybody
is so keen on the idea that spinosaurids spent most of their time in water
Sues et al. (2002) point out that the long narrow snouts of spinosaurids and
piscivorous crocodilians (e.g., gavials) are actually rather different.
Spinosaurids have flat-sided snouts that are convex on top, whereas the
snouts of fish-eating crocs are more tubular. Sues et al. (2002) suggest
that this morphology, like the extensive secondary palate, rendered the
spinosaurid snout less susceptible to bending stresses, and was not a
piscivorous adaptation per se. They also suggest that the shape of
spinosaurid teeth (conical or only weakly recurved) are "consistent with
their use for impaling and holding prey". All in all, they suggest that the
jaws of spinosaurids were adapted for seizing small prey. The authors
"The skull of _Irritator_ does not appear to be well-suited for catching and
processing large, resistant prey. Its structure differs from that in other
large theropod dinosaurs such as _Allosaurus_ (Rayfield et al., 2001) and
_Tyrannosaurus_ (Erickson et al., 1996), presumably reflecting different
modes of feeding. Most likely spinosaurid theropods rapidly and forcefully
seized smaller prey, which was then processed by dorsoventral motion of the
head facilitated by the powerful neck musculature. (Extensive side-to-side
striking movements of the head, as employed by extant crocodylians, appear
unlikely in view of the narrow occiput as well as the weak development of
the basal tubera.) Whereas fish formed part of the diet in at least _B.
walkeri_, there is nothing to suggest that spinosaurids were exclusively or
even predominantly piscivorous. Previous anatomical comparisons between the
feeding apparatus of crocodylians and spinosaurid theropods were based only
on superficial resemblances. The postcranial skeleton of _Baryonyx_ lacks
any obvious specializations suggestive of an aquatic or semiaquatic mode of
life (Charig and Milner, 1997). Charig and Milner (1986, 1997) interpreted
the greatly enlarged and strongly curved ungual of manual digit I as a
?gaffing? device for catching fish, but this intriguing hypothesis remains
untestable in the absence of a close analogue among extant tetrapods."
Also, don't forget that there is evidence that pterosaurs were also part of
the spinosaurid diet. The remains of one pterosaur were found with a
spinosaurid tooth embedded in its neck vertebra.
Buffetaut, E., Martill, D., and Esculli, F. (2004). Pterosaurs as part of a
spinosaur diet. Nature 430: 33.
Sues, H.-S., Frey,E., Martill, D.M., and Scott, D.M. (2002). _Irritator
challengeri_, a spinosaurid (Dinosauria: Theropoda) from the Lower
Cretaceous of Brazil. Journal of Vertebrate Paleontology 22: 535?547