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RE: What did Spinosaurus eat? New species of Lepidotes found
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.
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
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
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.
Jaime A. Headden
The Bite Stuff (site v2)
"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion