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



2011/3/3 Don Ohmes <d_ohmes@yahoo.com>:
>
> So -- perhaps a look at spinosaurid anatomy from the design perspective of
> lifting vertically a "wiggly" weight that has been grasped by the jaws would
> be interesting? As you say, the forces would be transmitted along the long
> axis of the snout in a straight pull-back of the head, and this is true even
> when the front limbs are not actively engaged.
>
> It would seem reasonable to assume (as a working hypothesis) that any fish
> too big to swallow whole, but small enough to be lifted would be transported
> to shore for processing -- much as river otters do -- and that processing
> would not be extremely demanding, in itself.
>
Looks like a good idea, Don. Perhaps in this spinosaurids, with their
relatively taller than wide snout, may surpass crocodilians, if the
fish was carried with the skull oriented horizontally (more resistant
the skull would be, with heavier fishes, if these were carried with
the skull held vertically, as I suppose you are talking). But, is
there evidence of this transport behaviour in fishers with long, and
presumably more fragile, snouts?

Other random thoughts

-Sorry, Tim, but I erred when saying that spinosaurids have taller
than wide snouts. This is true for baryonychines, but according to Dal
Sasso et al. 2005, not of Spinosaurus, at least at the upper jaw.
However, the lower jaw seems to be taller than wide, especially
caudalwards.

Now sorry again Tim, but I will play Devil's advocate with the
longirostrine fish-eating bird model:

-I think that the bird models have some adventages. First, it seems
spinosaurids were no specialized swimmers, as far as can be seen from
baryonychines, and would more resemble wading birds in locomotor style
(although another problem: their limb proportions more closely
resemble the short-limbed paddling birds!). Spinosaurines may have
better swimming abilities (unknown because of the lack of limbs), but
parsimony and the sail/hump do not suggest so. Second, the short
secondary palate found in spinosaurs is found in a more extended
fashion not only in crocodiles, but also in many long-beaked water
birds, as the Mycteria skull I have, whose tip may have been subjected
with similar bending stresses to those described by Rayfield et al. in
the case of Baryonyx and the gavial by dealing with similar prey
items. Third, the longer neck may help with a source of precision
crocs seem not to have. Four, the back of the jaw apparently permiting
to increase the gape (if I got well David Marjanovic's mention on
this).

-The Rayfield et al's 2007 paper does not make comparison with
fish-eating longirostrine birds, just with tall-snouted theropods,
alligators, and gavials. Thus, on the basis of their work, I would not
say that longirostrine birds are worst analogs than gavials.

-Many of you may want to kill me, but may the size of the sail/hump
helped an aquatic spinosaur forming a shadow which permitted fishes to
approach?

-Regarding the Bailey's hump hypothesis... May the large size alone
and the peril of isometry for the same function explain the robustness
of the spines of sailed dinosaurs relative to those of large non
therapsid synapsids? One may think that, if supporting these dinosaurs
were humped, that the spines would be much stouter than (instead of
similar to) those in the humped mammals with which Bailey compared,
accepting that isometry is bad idea in differently sized animals.

-If Spinosaurus had a weak bite as here hypothesized he may had as
much chances against a Tyrannosaurus as a greyhound has against a
pitbull even when the former is slightly larger than the latter!

Cheers,

Augusto