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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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