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Re: cause of Gigantism in sauropods



2011/2/8 Augusto Haro <augustoharo@gmail.com>:
> Contrarily, at least for carnivorous mammals, it seems that larger
> carnivores are the ones that generally hunt relatively larger prey,
> according to Carbone et al. (2007). ....
> As the size range, and probably physiology of carnivorous
> mammals is not necessarily the same as for non-avian theropods, we
> can't be sure what way dinosaur proportional prey size scaled. I am
> not aware of similar scaling studies in carnivorous birds and crocs,
> which would be better to infer the dinosaurian condition than mammals.
>
> Reference:
> Carbone C, Teacher A, Rowcliffe JM, 2007 The Costs of Carnivory. PLoS
> Biol 5(2): e22. doi:10.1371/journal.pbio.0050022
>
Now I think that the positive scaling of relative prey size to
predator size may hold for dinosaurs, given that it does not seem to
be restricted to mammals among amniotes. As far as I observed, little
crocodiles do not seem to attack prey they have to dismember in order
to swallow (just relatively small locusts and frogs), while adult
crocs can dismember prey and would so kill animals near their weight,
as zebras. Small varanids seem to focus on stuff smaller than
themselves, while the Komodo dragon (ok., thanks to venom, but this
does not counter the scaling) can hunt ruminants well above its size
(a friend made me note this). So, perhaps large theropods, generally
speaking, were to be expected to hunt proportionally larger prey size
when there was a size increase. At least for tyrannosaurids, this may
explain the increase in the adductor musculature in the larger
Tyrannosaurus than in the smaller tyrannosaurids (if it had to deal
with proportionally larger prey with proportionally thicker bones).
Still, this not necessarily implies they had to hunt adults, perhaps
just proportionally larger juveniles (not necessarily larger than
itself, because the scaling parameters may not be the same as for
mammals).