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



I have a little difficulty in viewing gharial-like or Crocodylus-like
fish-catching lateral movements in spinosaurs: spinosaur snouts are
more laterally compressed than crocodile skulls, which are more
dorsoventrally compressed, and better for lateral motion. Perhaps
there can be some analogy with the gharial but adapted to an arc of
movement on the sagittal plane (mantaining the jaws open, at least
when the snout closely approaches the fish) when the neck and head
locate in this plane, of course? The longer dinosaurian neck may have
permitted more widespread and faster dorsoventral movement of the jaws
than in crocodiles. May moving the skull ventralwards permit the hook
at the tip of the upper jaw to tend to envelope the prey, for a more
secure grip? In the hooked shape of the tip it may better resemble the
shape of the snout of tact-fishing Mycteria storks than either herons
or gharials (I am not throwing a Mycteria-like model now, just a
puntual similarity). The sensory pits at the tip of the snout may be
also good with this motion as far as the tips of the snout are
submerged, and may help in dirty waters.

The short hindlimbs of spinosaurs when compared with wading birds
suggests they were more submerged than these, if attempting to hunt
fishes proportionally similar in mass; more so if the fishes are
proportionally larger (if there is a relative prey size scaling
similar to that in mammals, and at least during ontogeny, also
varanids and crocodiles). The possible sail of aquatic spinosaurs do
not seem to make good fins, because they are so rigid and much
longitudinally extended. It looks like they would be an hidrance while
turning if the animal was completely submerged. Thus, the sail may be
supposed to be kept out of the water. In this case, it may indicate
the importance of keeping thermal conducting relations with air while
the body was submerged. That the nares do not show a dorsal location
may suggest a less submerged head than in crocodiles and phytosaurs,
in this more akin to wading birds. If the neck was farther from the
horizontal than in those crurotarsans, and the pits in the snout
indicated it was in the water, it seems that the sail, caudal part of
the skull and cranial part of the neck would not be submerged.

In case Bailey is right with his hump hypothesis, the hump may suggest
aquatic habits if heavy when supported on two feet (accepting Jaime's
and Andrea Cau's reconstruction of the hump centered closer to caudal
extremity of the body). Although of apparent little use in water, it
may help a piscivore if the resources of a river dwindle and it has to
search other rivers, although here I bit my tongue because the hump,
if heavy, would have to be supported out of the water when searching
rivers.