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Re: What did Spinosaurus eat? New species of Lepidotes found
On Wed, Mar 2, 2011 at 3:21 AM, Don Ohmes <firstname.lastname@example.org> wrote:
> Granted, the heron analogy is obviously incomplete or even wrong in some
> details, but gavials are limited by their anatomy entirely to lateral
> strikes, are they not?
Yes. Crocodilians as a whole typically strike their prey from the
side. The longirostrine (long and narrow) snout minimizes allows the
tip of the jaws to sweep through the water faster, but is specialized
for attacks on small, agile prey. The gavial fits this category, as
do certain other long-snouted crocodilians (e.g., _Tomistoma_ and
_Crocodylus johnstoni_). Crocodilians with a slightly shorter snout
(mesorostrine) include forms that are generalists that have a taller,
narrower snout (e.g., _C. porosus_, _C. niloticus, _Melanosuchus_)
with the rostral morphology better able to resist the forces
associated with catching targeting larger prey; and mesorostrine forms
that have a flatter, wider snout (playtrostral; e.g., _Alligator
mississippiensis_), which seems an alternative to the longirostrine
morphology for targeting small, agile prey, but with an improved
capacity for medium-sized prey. Then there are the many short-snouted
crocodilians, which seem to prefer slower aquatic prey, as well having
as terrestrial component to their diet.
As far as rostral morphology goes, based on Rayfield &c's work, the
closest analog for spinosaurs is the gharial rather than the
alligator. The longirostrine condition indicates a predisposition to
piscivory (though not exclusive), and for rapid lateral strikes
underwater. Overall, the data point to spinosaurs similarly targeting
small underwater prey via lateral strikes. This in turn argues that
spinosaurs held the rostrum underwater as a prelude to the strike,
since the entire lateral motion was executed underwater. The jaws
could also handle small terrestrial prey. The fossil evidence tells us
that the spinosaur diet included fish, small ornithopods, and
pterosaurs - all consistent with this interpretation.
> Therefore, the proposition that rosettes are only useful in lateral strikes,
> and could not evolve within other planes of attack, does not seem valid.
> Er, not that you are explicitly stating that, but it seems to follow from
> your post, so I thought point below should be made.
Yes, I take your point. And as you acknowledge, I wasn't actually
commenting on the prey-catching abilities of herons. I agree that the
heron's prey-catching strategy is constrained by its heritage.
Nevertheless, the point remains that the heron serves as a poor analog
for the trophic ecology of spinosaurs.