[apologies for the empty post before, i don't know what hotmail's doing. this is what it was supposed to say:]
>So given some abstract biomechanical reasoning that says no animal can
>grow heavier than 140 tons, and some bones that suggest an animal damn
>well _did_ grow heavier, I know which one I will believe :-)
But isn't there a question of wether or not the bones do suggest this?
I don't know much about this area beyond R McNeil Alexander's "Dynamics of Dinosaurs and Other Extinct Giants" (at least ten years old i think), but assuming the method (i.e. measure the volume of a model, assume an average density based on living animals, and calculate the mass from that) described in that book was used for the weights given in the earlier post, there is the obivous problem of what density to assume.
In "Dynamics" the author references estimates of the average density of crocodiles, because they are close relatives of dinosaurs. But crocodiles are obviously nowhere near giant sauropods in size, and i would assume that - if there is a restriction on mass - giant sauropods would presumably have adaptations lowering their average density - adaptations for which there would probably be no living analogue. So i'm guessing that using any living animal to estimate mass would be inherently flawed if the sauropods did approach the weight limit. (i just had an image of low density sauropods floating away in a breeze...)
What are sauropod bones like on the inside?
And questions of density aside, the volume used in the calculation ultimately depends on it's sculptors interpretation, and large sauropods do seem to often be known from incomplete skeletons as far as i know.
Having said that, how strong are the calculations that give the upper mass limit? Do they make any assumptions about the structure of the legs? Would the calculations need to assume a certain ability to support weight? Would they assume anything about the way the animal's weight was distributed? Or is it just a back-of-the-envelope calculation based on a simple model, like a block with four pillars or something? And if so, is this valid? (I beleive i read in "The Dinosaur Heresies" that the claim that _Quetzalcoatlus_ couldn't fly was based on simple models that didn't take into account the complexity of structure that a living animal can have, or something along those lines.)
Or were all these things accounted for - 170 tonnes *does* fall within the 100-1000 tonne range given by the abstract Mike referenced?
[I'd also like to join everyone else in expressing my deepest sympathy to everyone affected by the tragedy in the US. I don't think i can add anything new.]