Re: Brachiosaurid metabolism?

[dinoboygraphics@aol.com]

There are several problems with this discussion.  First of all, just 
because someone published a mass estimate does not make it plausible.  
There is no way you can get more than 40 tons onto a normal African B. 
brancai.  And the largest specimens of B. altithorax probably don't 
exceed 50t, unless it differes even more from the African species than 
is thought.

Second of all, as David has asked, where on Earth is the growth-rate 
estimate coming from for a 5t Hypselosaurus to take 8-11 decades to 
grow up?  The only in-depth osteological study I'm aware of for 
sauropod growth  is Currie-Roger's work on Apatosaurus.  This (much 
larger) sauropod was growing up in a time frame on teh order of 2 
decades, not 8.  If Hypselosaurus took more than 8-10 years to grow up, 
it was really dawdling by sauropod standards.

As for metabolism in sauropods; it's clear that the kind of growth that 
has been empirically determined for them requires a metabolic rate 
higher than in extant lizards and crocs, although how much higher 
cannot be precisely determined.  The airsac respiratory system of 
sauropods is consistent with elevated aerobic capacity (i.e. they were 
probably physicall active), but that needn't imply a body temperature 
as high or as stable as most placental mammals, let alone most birds.

Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333

www.skeletaldrawing.com

-----Original Message-----
From: david.marjanovic@gmx.at
To: dinosaur@usc.edu
Sent: Wed, 22 Nov 2006 7:41 AM
Subject: Re: Brachiosaurid metabolism?

> If you take e.g. a smaller european sauropod _Hypselosaurus_ with
> a mass of some 5300 kg when it was adult,  compare it to the hatchling
> weight of the same genus (2,4 kg) and use the calculated grow rate,

Wait, wait, wait.

Firstly, *H.* is a quite fragmentary affair. Remember that mass 
estimates of
*Brachiosaurus*, for which the complete skeleton can be reconstructed 
from a few
individuals, range from 15 to 75 t (ignoring even higher outliers for 
the
moment), and then have another look at *H.*...

Secondly, there's no evidence that any of the many oospecies from the 
Campanian
and Maastrichtian of southern France belongs to *H.*. For a long time 
*H.* was
the only named sauropod from that general time and place, but now 
there's
*Ampelosaurus*, too...

Thirdly, where does the estimate of hatchling mass come from?

And lastly, what growth speed estimate are you using?

> And because much larger sauropods such as _Brachiosaurus_ weighed
> seven or more times as much as _Hypselosaurus_,

or three or less...

> So then there's a theory I kind of like wherein sauropods were
> endothermic upon hatching and then their metabolisms gradually
> slowed as they got bigger. But, it's hard to tell and
> noone seem to favour it anymore.

One reason for this is that ecto- and endotherms differ in the 
composition of
their cell membranes (those of endotherms are more permeable for sodium 
ions).
Another is that it's difficult to imagine how an ectothermic animal of 
that size
could have functioned.
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