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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 catching fish.


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 conclude:

"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.


References

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