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Re: Brachiosaurid metabolism?



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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