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



2011/2/28 Tim Williams <tijawi@gmail.com>:
>
> The closest analog or 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.
>
This hypothesis bears more data behind, and should be thus the most
respected, but, it seems to me that the point by Jaime regarding the
irregular tooth file arrangement seems to suggest some similarities
the predatory habits of Crocodylus, although with less bite force
(which would resemble more the gharial).
Also departing from the gharial, the lower jaw does not seem to be
much more dorsoventrally thin than in other dinosaurs, contrasting
with gharials, nor is the rosette so much widened (a relatively not
so-widened rosette is also present in Crocodylus).
Long snouts seem to permit a faster grip of prey, because an angularly
similar lateral head movement relative to the neck would move the tip
a longer distance, and may be an advantage also at land (perhaps this
explains they being able to capture presumably fast prey as
pterosaurs, if not slow or already dead before capture; now I sin of
spreading rumor, but I heard of storks being able to capture
passeriforms).
The hook at the tip may help retaining the prey which tries to escape
away from the predator, or getting a piece out of it, as in the case
of carcasses for the birds Jaime mentioned. Anyway, this hook seems to
depart from the gharial condition.
The irregular tooth row implies a longer alveolar border of the jaw (I
was to say that this suggests more teeth and thus better grasp, but I
am not sure), with which perhaps to grasp prey more securely.
Alternatively, it may permit a small group of teeth at the tip of each
"mount" in the irregularity to put more pressure (and thus to
penetrate more) in the food item, because teeth closer to the
"valleys" would contact the prey in a lesser degree.
As far as I know, Crocodylus for the most rely on fishes and other
relatively small aquatic animals as frogs, aquatic snakes and crabs.
Perhaps the gharial is more specialized for fast, small fishes, while
Crocodylus hunts a larger variety of fishes, with possibilities for
swallowing larger fishes in the wider jaw. The jaw articular mechanics
indicated by David Marjanovic may suggest swallowing of relatively
larger fishes.
May spinosaurs have been something more similar to a mix of the
gharial, Crocodylus, and heron (at least for the jaw articular
mechanism related to large-prey swallowing)? To me, Proterosuchus and
phytosaurs look like better candidates for similarity in habits, but
they are extinct.

Regarding Majungasaurus, Lucas Fiorelli recently described several
bite marks in a peirosaurid crocodile 3-4 mts. long which he
attributes to large theropods, suggesting as culprits either
charcharodontosaurids or abelisaurs
(http://crilar-conicet.academia.edu/LucasFiorelli/Papers/352183/Predation_Bite-Marks_on_a_Peirosaurid_Crocodyliform_From_the_Upper_Cretaceous_of_Neuquen_Province_Argentina).
What if in the Mesozoic there was the possibility of eating 4 m.
crocodiles for a living, a niche we do not find today because
carnivorous mammals are not large enough? Eating crocodiles would be
easier if there were no larger crocodilian species (Sarcosuchus or
Deinosuchus) around. Coping with he hard hide of the crocodiles may
relate to the relatively rigid skull of Majungasaurus. Catching a
crocodile seems to require less reflexes than catching faster swimmers
as fishes. This may need to check if there was a large crocodilian
population... the hypothesis may imply that the Majungasaurus teeth
were prone to break up often if hitting osteoderms, and this may be
tested checking the wear in Majungasaurus' teeth compared with other
carnivores supected of eating more tender stuff.