03-November-2008, 03:34 AM
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Established Member
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Join Date: Jun 2007
Posts: 1,045
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Pterosaur Size & Mass
There does seem to be an issue with larger and larger flying animals. Compare Argentina Magnificens to Quetzalcoatlus.
Estimates of pterosaur mass.
http://www.flickr.com/photos/markwitton/1386125619/
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Despite this, most pterosaur workers have been happy to estimate the masses of pterosaur bodies with single densities and, thanks to thoughts that pterosaurs had next-to-no soft tissue, pterosaur mass estimates are typically low. Like, really low. 16 kg for a 7 m span Pteranodon, sub-100 kg for a giant 10 m span Quetzalcoatlus, that kind of thing. Are these figures right? Well, to test this, I’ve tried to put together a method of estimating mass without going anywhere near soft tissues. No density required here, folks: just skeletal anatomy. Y’see, the dry mass of a skeleton is directly proportional to body mass in modern birds and mammals, and, intriguingly, the scaling relationships is nigh-on identical in both animal groups in spite of obvious differences in ecology and phylogeny. Armed with an array of 18 different pterosaur skeletal masses determined using geometric modelling and a regression analysis of bone wall thickness – bone shaft diameter to estimate skeletal pneumaticity (pterosaurs have hollow bones, folks), I plugged my modelled pterosaur skeletal masses into the skeletal-mass to body-mass regression and voila, total pterosaur masses estimated with no consideration of soft-tissue density at all. Just so you know, my masses of a giant 10 m span Quetzalcoatlus were around the 250 kg mark, while a tiny 30 cm span Anurognathus masses in at 39 g or so. This is potentially pretty neat but, erm, there’s one big problem: my masses are approximately three times greater than anything that’s gone before. Oh.
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This, of course, creates the question of who’s barking up the wrong tree. Are my pterosaurs ridiculously heavy, or are other pterosaurs unfeasibly underweight? Judging this is difficult: without having a pterosaur land on a set of scales we’ll never know how great their masses really were, but four points are worthy of consideration on this issue.
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Number one: My estimates correlate with bird masses of the same wingspan very, very well. Of course, we don’t have any birds with wingspans greater than 3 m today, but it’s reassuring that the pterosaurs I modelled beneath 3 m are not unreasonably heavy compared to their avian counterparts. Granted, we need to be careful comparing pterosaurs to birds in this manner, but at least modern birds demonstrate that animals of these masses and wingspans can fly.
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