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



2011/3/2 Tim Williams <tijawi@gmail.com>:
> On Thu, Mar 3, 2011 at 6:48 AM, Augusto Haro <augustoharo@gmail.com> wrote:
>
> So I think you've convinced me
> that a gavial-like lateral sweep would not have worked as well in
> spinosaurs.
>
Thanks! not always can one convince the wisemen of the DML! (no irony
intended). But, this positive feedback has the bad effect of
stimulating my tendence to wild speculation : ).

I have read little about bite forces in theropods, but what I read
suggests me they have proportionally lower bite forces than crocodiles
or similar size, and from what I have observed of their adductor
chambers, relatively smaller brains and generally proportionally
larger skulls, non-avian theropods, generally speaking, seem to have
had greater bite forces than birds if we discount size. So it seems
they are kind of intermediate in bite force.

Thus, it seems that spinosaurs would be disventaged relative to
crocodiles on the basis of their bite alone. Their skull seems to me
more fragile than even gharials in two things: 1-Secondary palate much
more restricted than in the Crocodylia (in Spinosaurus and
Suchomimus). 2-Larger antorbitary fenestra of Suchomimus and
Irritator. Alrthough, as you indicate on the basis of Rayfield's et al
work, this does not deny that at least the tip of the snout was
subjected to similar forces to those acting on the gharial.

But I think spinosaurs (at least baryonychines) have something neither
modern crocodiles or wading birds do have: strong arms capable of
pushing the food item far from the head while the snout is pulled
backwards with the neck muscles in order to tear the prey in smaller
pieces. Indeed, the curve, serrated teeth of baryonychines seem to fit
with the hypothesis of tearing, although this does not hold for
spinosaurines: this may suggest at least slightly different prey
catching behaviours in both groups. In this they may resemble
cathartid vultures, which do tear with a relatively elongate and
fragile snout, although holding the food item with their more
elongated hindlimbs. The curved tip of the upper jaw of Cathartes (and
gulls and certain procellariiforms) may be mimicked with the curved
tip of the lower jaw of spinosaurids. Tearing seems to subject the
elongate and fragile cathartid skull with a tensional force aligned
with the long axis of the beak, and thus, the sense in which the beak
is more resistant. The elongate snout of spinosaurids would have
similarly been most resistant to tearing.

The straighter, not serrated teeth of Spinosaurus suggests less
reliance on tearing (I do not know about the power of the arms in
spinosaurines, but it seems parsimonious to think of them as not
reduced, taking into account the basal tetanuran condition). However,
their relatively larger teeth at tip of the jaws may suggest greater
capability of severely harming a fish prey with a single bite.