RE: Swiming spinosaurus

[GUNTER.VANACKER@ELECTRABEL.COM]

I think it's very unlikely that spinosaurids spent much under water (or
actually swimming).

Here is how I see the behaviour of spinosaurids :

The similarities with crocodiles are mainly (?exclusively) in the skull; the
low, long skull also had a "kink" (which led some researchers to suggest a
close relationship with the basal theropods Dilophosaurus and Coelophysis),
and teeth unlike any other dinosaur teeth. All these features indicate that
spinosaurids actively hunted fish, however, I do not believe that they
pursued fish while swimming, but that they caught fish like most bears now
do; looking for fish while standing on the shoreline (or the waterline to
their knees at most). When the spinosaur spotted a fish, the theropod would
use its powerful hands, with the large thumbclaws, to grab it (like most
basal tetanurans such as allosaurids and megalosaurids, spinosaurids had an
unusually large manual ungual I). The theropod would often immerse its head
(but not the rest of its body) under water to look for fish, or actually
catch them if he had the chance.
While the specialization of the skull shows that fish formed the bulk of the
spinosaurid-diet (we have evidence, fish-scales were found associated with
the type specimen of Baryonyx walkeri), it also scavenged when possible
(Iguanodon bone fragments were also found associated with Baryonyx).
The spinosaur postcranium (skeleton without cranium and mandible in this
case) looked like most theropods, which were all terrestrial animals. Most
dinosaurs probably did swim or "paddle" for short distances when necessary,
but did not pursue prey in this way.
If Spinosaurus needed some kind of underwater "sensor", then a large dorsal
sail would have been like shooting a mosquito with a mechanized artillery
canon.

On the "sail" of some spinosaurids :
the image of spinosaurids with a dorsal sail is based on the now lost
holotype of S. aegypticus
(only drawings remain). It has been suggested that the vertebrae of the
holotype specimen were not associated with the skull and other remains, but
that they belong to a high-spined allosaurid or even a completely different
type of dinosaur. Remember that better-known spinosaurids like Baryonyx
walkeri and Suchomimus tenerensis don't have a dorsal sail (their vertebrae
are not much higher than other types of theropods). Other differences
between baryonychines and S. aegyptiacus appear to be based on some subtle
differences like the number of teeth.
Let's assume that S. aegypticus did have a dorsal sail; after all Stromer
was a very thorough scientist.
Northern Africa housed other dinosaurs with dorsal sails; the diplodocimorph
sauropod Rebbachisaurus garasbae probably, and the iguanodontian ornithopod
Ouranosaurus nigeriensis certainly had one, all were more or less
contemporary, but belonged to totally unrelated groups of dinosaurs. It is
very unlikely that all these animals possessed a sail to regulate their
body-temperature, this view was primarily based on Dimetrodon, an animal
that is often mistaken for a dinosaur. As far as I am concerned all these
dinosaurs were "warm-blooded" (I don't want to start another debate on this
topic, but you know what I mean).

The sail could have had 2 possible functions :

1. display; either to make the animal more attractive to the opposite sex,
or to make it look more menacing and larger when confronted with a
competitor

2. Since the unrelated Spinosaurus, Rebbachisaurus and Ouranosaurus all seem
to have had a dorsal sail, and they all had different behaviour (a carnivore
and 2 herbivores with different feeding strategies), it's possible that the
evolution of a sail-like structure was triggered as an adaptation to an
unusual environment. The mid-Cretaceous North Africa may have known long
seasons when food was scarce (e.g. few plants because of drought, which
forced herbivores to migrate), and the "sail" was actually more a sort of
"hump" where fat was stored when food was abundant. This theory has been
forwarded before.



Regards,

Gunter Van Acker




-----Oorspronkelijk bericht-----
Van: ville sinkkonen [mailto:ville_sinkkonen@artic.net]
Verzonden: maandag 9 juli 2001 11:13
Aan: dinosaur@usc.edu
Onderwerp: Swiming spinosaurus


HI


A while ago there was discusion a new theory of the spinosaurus sail.
I'n the theory it was suposed that the sail was used to sensories to water
bounce.

I dont know what kind of tale Spinosaur had,
but if it was crocodilian like it could probably swim.

The head is wery crocodilian like,
and the sail could be sensoring water bounce.

The sail must have many other kinds of accounts.
When the spinosaur get out of the water it may be basking on the sun to warm
up.

But the main reason that it must have been used in display.


With best regards: ville sinkkonen

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