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Re: Vertebrae of Early Sauropods



--- PATRICK JOHNSON <mrpatjohnson@msn.com> wrote:
> Dear Mark,  
> 
>    Thanks for the information. I'll see if I can
> find the issue of JOURNAL OF VERTEBRATE PALEONTOLOGY
> by Mat Wedel by going to the journal's web site.  If
> not, I'll contact Mat directly via his email adress>
which you provided me with.
> 
>    There is more to this then finding evolutionary
> links. It makes sense that the sauropods evolved a
> lighter vertebrae structure as they evolved into
> more massive size.  But I recall reading two
> published results of attempts to make computer
> models of apatasaurus based on reasonable
> physiological assumptions.  
>     One of these focused on the muscular ability of
> apatasaurus to raise its neck and head. A main
> assumption in the model was that the neck muscles of
> apatasaurus were as strong as the muscles of a
> modern crocodile.  As it turned out, the computer
> modeled apatasaurus could not raise its long neck
> much above the height of its shoulders.

I haven't come across this study. Can you point out
where I could get a copy?

>     The second study was concerned with blood
> pressure. According to the computer model for this
> case, an apatasaurus could not have raised its neck
> to a great height - because, if it did, the blood
> pressure required to raise the blood to the brain
> was more than its circulatory system could provide
> without giving the creature an immediate heart
> attack plus fatal cerebral hemmorage.

There are some good counter-hypotheses to this, some
of which were originally pointed out to me by Guy
Leahy. The main points are that while the blood column
in a vertical or sub-vertical sauropod neck would be
high, perhaps as much as 700 hg., sauropods may have
had a more avian than mammal-like vascular physiology,
resulting in possibly higher systolic blood pressures
for their sizes than might be expected in a giant
mammal with a more typically mammalian cardiovascular
system. Many mammals, for example have systolic blood
pressures that are 110-120 mm hg, while in birds it
may be 150-175. As for the problem of high blood
pressure, in domestic turkeys this can actually be up
to 400 mm hg. Sauropods probably did have huge hearts,
but for a c. 30 tonne diplodocid like Barosaurus I
think a heart equal to 1.0% of its body mass, or
300kg, wouldn't be out of the question.      

>     But its hard for me to imagine that apatasaurus
> and even larger sauropods could have walked around
> with their necks in a nearly horizontal position -
> unless they were in an environement free of large
> predators that would surely have made great use of
> oppurtunities to take a critical bite out of their
> long, exposed, horizontal necks - and that does not
> seem to be the general case.

A good point. I think they would have been extremely
vulnerable had they habitually done this most of the
time. 
> 
> Well, if there were no mysteries to solve about
> dinosaurs, they wouldn't be so fascinating.
> 
> Thanks again.

Thanks to you, too, Patrick. --Mark Hallett 

      > ----- Original Message -----
> From: Mark Hallett
> Sent: Wednesday, March 24, 2004 9:15 PM
> To: mrpatjohnson@msn.com
> Subject: Re: Vertebrae of Early Sauropods
> 
> Dear Patrick, From my reading and studies I believe
> you are correct in this assessment. You might want
> to
> read Mat Wedel's recent paper on the pneumaticity of
> sauropod vertebrae that appeared in the (July?) 2003
> issue of JOURNAL OF VERTEBRATE PALEONTOLOGY. Mat can
> be contacted at >sauropod@socrates.berkeley.edu>
> Best Wishes, Mark Hallett
> --- PATRICK JOHNSON <mrpatjohnson@msn.com> wrote:
> > >From my meager sources, I've read that the
> > vertebrae of cetiosaurus is relatively solid in
> > comparison with "more advanced", larger sauropods.
>  
> > This leads me to suspect that the same can be said
> > for other early sauropods, particularly vulcanodon
> > and barapasaurus. And then, by backwards
> extension,
> > it seems to me that the same should apply to the
> > prosauropods.
> >  
> > I'd appreciate it if anyone would confirm or
> correct
> > me regarding this.
> >  
> > Thank you in advance.
> >  
> > Patrick Johnson
> > mrpatjohnson@msn.com   
> >  
> 
> 
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