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



David Marjanovic <david.marjanovic@gmx.at> wrote:

> Spinosaurid jaws were not covered by a beak (and indeed a beak wasn't
> necessary with such teeth). This means there is no reason why the jaw tips
> should have become pointed; pointed jaw tips would only have become injured
> more easily and would not have conferred any benefits.
>
> Seen from the other metaphorical direction: because herons lack teeth,
> stabbing prey with their beak is the only option they have, so that is what
> they are adapted for.


The closest analog for spinosaurs among modern crocodylians appears to
be the gavial (or gharial, _Gavialis gangeticus_).  The gavial is the
closest analog both structurally and biomechanically (Rayfield et al.,
2007; JVP 27: 892-901).  The gavial is a longirostrine crocodilian in
which the rostrum ends in a terminal 'rosette' - as in spinosaurs.
The thing is, in order to catch fish, the gavial favors lateral
sweeping strikes with its rostrum.  In fact, the longirostrine snout
appears to be specialized for this kind of predation: rapid movement
through water by lateral flexion, with the prey caught at the end of
the rostrum (McHenry et al., 2006; Anat. Rec. 288A: 827-849).  If this
also applied to spinosaurs, this is inconsistent with a heron analog
for spinosaurs, because herons employ stabbing motions with their
rostrum to procure fish.


Further, the gavial analog suggests that the spinosaur rostrum was
already immersed in water when the predatory strike is launched.  So
the spinosaur rostrum wasn't above or by the water surface, but below
it.  This makes sense if one of the targeted prey items for African
spinosaurs were giant lungfish, which (going by the behavior of modern
_Neoceratodus_) spend most of their time lurking on the bottom of
rivers.


Cheers

Tim