The Hunchback of the Mid-Cretaceous [Was: Re: Swiming spinosaurus]

[Jura <archosaur@reptilis.net>]

--- "Mickey Mortimer" <Mickey_Mortimer11@msn.com>
> wrote:
>Steven Coombs wrote-
>
>> I heard and read about the "hump theory", and I do find somethings wrong
>> with this theory, how could an animal have something like this on its
>back.
>> There would be too much weight distributed on the back of the animal, the
>> animal would be a struggleing with it whnever it moved! From the remains
>of
>> the neural arches they were quite slender(It would be really imposible to
>> hold it up much), and if it did have a hump, would it be more plauseable
>> that it would have had air-sacs just like some giant Sauropods such as
>> Sauroposeidon in there neck, to take off a bite of the weight? And why do
>> they bring this up more on Spinosaurus than other animals presumed to have
>> sails such as Ouranosaurus, and it lived on the same continent as
>> Spinosaurus and the same type of environment? Aleast Ouranosaurus has
>> remains while Spinosaurus remains just dust!
>
>I strongly suggest you read Jack Bailey's (1997) paper on the subject.  He
>performed biometric analyses showing the spines of most sail-backed
>dinosaurs are similar to those of humped mammals, mostly artiodactyls.  This
>means the narrowness is not an issue.  Remember that most theropods were
>rather laterally compressed, so the hump would not have been much more
>hindering than the whithers of a bison (which in some extinct species like
>Bison antiquus actually equals Spinosaurus in neural spine height).  Of
>course, Spinosaurus was probably bipedal, but it could have had very robust
>limbs, an elongate tail for counterbalance, or even have been partially
>quadrupedal, as spinosaurids do have robust and elongate forelimbs.  Bailey
>examines all types of humped dinosaurs, including Spinosaurus,
>Acrocanthosaurus, Rebbachisaurus, Ouranosaurus and Barsboldia.
>
>Bailey, Jack Bowman, 1997, Neural spine elongation in dinosaurs:
>sailbacks or buffalo-backs?:  Journal of Paleontology, v. 71, no. 6, p.
>1124-1146.

++++++++++++++++++++++++++++++++++++

Unfortunately Bailey's study only extended to pelycosaur synapsids and didn't 
bother looking at the sails of modern sail-backed reptiles.

It's too bad as it probably would have been the first comparative look at the 
sails of modern reptiles.

As to the spines of _Spinosaurus_, I think it might be best to remind everyone 
how different the spines on  spino were compared to other "sail-backed" dinos. 
One could make a valid argument for humps in _Acrocanthosaurus_ and tendon 
braces in _Suchomimus_, but _Spinosaurus_ has a huge, high set of spines that 
wouldn't be very good for humps (which would be huge) or tendon attachments 
(which would be overkill). I can't even see how a hump on this creature would 
even be physically possible. How could it hold up the weight of a 6ft tall 
hump? If it forced the animal to be quadrupedal (which it would certainly 
would, considering it's position) then it would be forced into a semi-sprawled 
pose with its forelegs, which are (presumably) pretty small to begin with. That 
wouldn't look particularly comfortable.

Also, the vertebrae were strongly opisthoceolus, making the back very flexible. 
If there was a hump there, then all that flexibility is lost (so why bother 
evolving it?), but if there was a spine there, then you suddenly have this 
dynamic display structure, which would seem far more plausible.

As to the size, while I've heard that they are apparently blade-like; these 
spines, I'd question how bison-like they really are. If one searches through 
the archives on this issue, one will find instances where spino spines are said 
not to have the expanded ends (for tendon attachment in bison) and an apparent 
"watermark" where one could see where a sail would start up.

Then there are the truely humped animals today (all mammals) which don't even 
need tall neural spines to begin with (e.g. camels), so I don't even see how it 
correlates.

Besides, desert reptiles seem to get along just fine by storing fat in their 
tails, mammals no longer have this option.

Anyway, sails seem to make more sense for _Spinosaurus_ to me. Humps just seem 
to bring up too many issues.


Jura

==
The Reptipage at: http://reptilis.net

Because reptiles are just cooler.

_____________________________________________________________
Visit http://freeservers.com to get a FREE Web site with a personalized domain 
and FREE Web-based e-mail.