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Re: dino-lice



2011/4/23 Tim Williams <tijawi@gmail.com>:
>
> I agree.  But I'm not sure what you're driving at here.  The earliest
> known alvarezsaur (_Haplocheirus_) has a grasping, trenchant,
> functionally tridactyl manus.  This was the template from which the
> truncated, functionally monodactyl forelimbs of derived alvarezsaurs
> evolved from.
>
My point is that I do not know if even Haplocheirus' or
Acrocanthosaurus strong, trenchant, tridactyl manus was useful for
trophic reasons as prey-securing. Years ago, we were discussing about
the possibility of climbing in basal paravians, and you indicated they
had not very movable articulations and wrists. I think grasping prey
also requires more mobility around wrists, a good deal of supination
(at least comparing with carnivoramorphan forelimbs), not just large
or trenchant claws. Regarding the insufficience of arm power or ungual
trenchantness to infer prey-manipulation, kangaroos are "bipeds" with
proportionally strong forelimbs and curved manual unguals, yet this
does not mean they are used to dispatch prey. They even seem better to
grasp than theropod hands. Basal ornithischians also had trenchant
claws, and even if Heterodontosaurus may have been omnivorous, it does
not seem to be the same for Eocursor. Although I have not in-depth
read Senter and Robin's work, by now I think that the evidence does
not indicate the forearm was used, just how it may have been used to
help the animal. However, to be fair (and less ignorant) I will read
it...

> For example, bringing branches to the mouth
> (ornithomimosaurs, perhaps therizinosaurs - although the huge
> forelimbs of _Therizinosaurus_ look to me to be defensive weapons);

Agreed on defense, and perhaps intraspecific offense, even with curved
claws. Regarding bringing branches to the mouth (as well as grasping
prey with hands), is it necessary when the neck+skull is longer than
the forearm?

> tree-climbing (scansoriopterygids, perhaps _Yixiansaurus_);

May be, but this is not a feeding use...
I suspect some aerodynamic or balancing function may be more likely
than a trophic one, for the principal use in both birds and crocodiles
has something to do with locomotion (although the locomotion permited
by the crocodile forelimb would be much different, and this points out
that perhaps it is artificial to aggregate such disparate functions
under the label of locomotion for phylogenetically).