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Re: 11th specimen of Archaeopteryx‏



Jason Brougham <jaseb@amnh.org> wrote:

> In other words, transitional forms that were adapting to tree climbing would 
> not be expected to instantly
> possess a fully reversed hallux and toe claws with all the same proportions 
> as in neornithines. We would
> expect them to have some changes from the ancestral morphology, and in fact 
> Paravians and, especially,
> basal avialans do.


I know where you're coming from.  But here's the paradox: Why was the
integument so elaborately specialized for aerial locomotion, but the
osteological changes for arboreality so minimal?


If basal paravians did roost or perch on branches, why didn't the pes
become opposable?  One argument raised against this is that a
cursorial/ground-foraging lifestyle deterred the development of a
hallux suitable for perching.  I frankly don't believe this.  Many
modern birds forage on the ground and roost in trees, and the hallux
is long enough to be employed for perching, and elevated enough to not
interfere with walking or running.  So IMHO, the reason why basal
paravians like _Archaeopteryx_ didn't have a pes adapted for perching
is simple: They didn't perch.  Or roost.


As for trunk-climbing.... that's a whole different ball-game.






Cheers

Tim