From: christopher robert noto <crnoto@midway.uchicago.edu>
Reply-To: crnoto@midway.uchicago.edu
To: Jura <archosaur@reptilis.net>
CC: Mickey_Mortimer11@msn.com, dinosaur@usc.edu
Subject: Re: The Hunchback of the Mid-Cretaceous [Was: Re: Swiming
spinosaurus]
Date: Wed, 11 Jul 2001 11:31:24 -0500 (CDT)
Well, it seems that this won't be resolved until a fairly complete
Spinosaurus skeleton is discovered. However, I thnk we can all agree that
elongated neural spines were evolved independently among various lineages
and used for different purposes. Pelycosaurs most likely used them for
jump-starting their metabolosm and display, while dinos like spinosaurus
or Acrocanthosaurus used them for display and muscle
attachment. Buffaloes and other mammals took advantage of them for energy
storage, since, as it was pointed out, mammals lost the ability to store
fat in their tails. I'm not sure when the idea of humped dinos came into
vogue, but I think we need to exercise some discretion when comparing
structures from very different lineages, which may have evolved these
elongated neural spines for completely different reasons. These
differences in structure may be all the more telling than trying to make
the structures of all these different organisms conform to a few
specified functions. I hope that I'm making sense here, y'know one never
can tell sometimes :)
Chris
On Wed, 11 Jul 2001, Jura wrote:
>
>
> --- "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.
>
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