RE: What did Spinosaurus eat? New species of Lepidotes found

[Jaime Headden <qi_leong@hotmail.com>]

David Marjanovic wrote:

"Well, no. It suggests that _its snout_ habitually entered the water.

Like the spinosaurs, it may have been a heron analogue."

A heron lacks teeth and is encumbered with a large pointy beak. Herons approach 
prey during acquisition by stabbing swiftly with partially opened jaws, to 
capture the prey between the halves of the beak. Rather unlike spinosaurids, 
any of them, in which the jaws are BLUNT at the tips, broad, rounded, and with 
large premaxillary teeth in front accompanying a mandibular "rosette." 
Descriptions of the terminal rosette, as in some crocs, implies that all of the 
rostralmost premaxillary teeth form a neat rounded colonnade, but this is 
misleading: spinosaurid teeth, especially the two premaxillae-pairs referred to 
it (Taqcuet and Russell, 1995 and dal Sasso et al., 2005) are longest in the 
first two pairs, greatly diminished distally; this pairs with a large terminal 
array of the mandible in which the largest teeth are NOT the most terminal, but 
immediately following them, producing a mandible that "fits" behind the 
premaxillae. Spinosaurids, in this sense, had something of an overbite. This 
does not compare well with herons ... but it does compare well with gulls. 
Gulls, especially albatrosses (*Diomedeiidae*) have a large rostral 
premaxillary nail that overhangs the dentary which opens rostrally into a 
trough; the mandible is thus expanded upward lateral and posterior to the 
temrinus right behind the nail, from where it declines into the remainder of 
the jaw margin.

http://2.bp.blogspot.com/_csUZUsPFZoo/SdAovR8KQbI/AAAAAAAAAU0/EdgmA0l6CMY/s400/albatross.jpg
http://en.wikipedia.org/wiki/File:Spinosaurus_skull_steveoc.jpg

The above links (top, diomedeiid; bottom, Spinosaurid after dal Sasso et al. by 
Steve O. C.) illustrates this better than my encumbered writing.

If we were to infer dietary habits from the mere shape of the rostrum, as David 
does in comparing spinosaurids to herons, then we would find that a snatching, 
probing, tearing process may be projected. I think this may better describe 
spinosaurid diet, especially as Rayfield et al.'s work implies a vertical bite 
with high torsion constraints, permitting precision biting far better than 
"snatch feeding" as in herons, anhingas, etc.

I am not sure about water-wading, but am fairly certain the dietary qualities 
were far broader than a giant animal stalking for a quick snatch: the jaws 
appear suited for processing larger animals, such as lungfish larger than its 
own head.

Dal Sasso, C., Maganuco, S., Buffetaut, E. & Mendez, M. A. 2005. New 
information on the skull of the enigmatic theropod Spinosaurus, with remarks on 
its sizes and affinities. Journal of Vertebrate Paleontology 25(4):888–896.
Rayfield, E. J., Milner, A. C., Xuan, V. B. & Young, P.G. 2007. Functional 
morphology of spinosaur 'crocodile-mimic' dinosaurs. Journal of Vertebrate 
Paleontology 27(4):892-901.
Taquet, P. & Russell, D. A. 1998. New data on spinosaurid dinosaurs from the 
Early Cretaceous of the Sahara. Comptes Rendus de l'Académie des Sciences, IIA: 
Earth & Planetary Sciences 327:347−353.

Cheers,

Jaime A. Headden
The Bite Stuff (site v2)
http://qilong.wordpress.com/

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


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