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Re: Feather Flap

Scott Hartman wrote:

I would side with Tim in that seed-eating is not necessarily indicative of arboreal habbitats. Seeds can and do fall to the forest floor, where even fully arborreal volant birds will go after them if their density and gathering costs are more favorable than the seeds still in the trees.

Yes - and it might be seasonal too.

Jeholornis does not seem to exhibit any particular adapations to arboreality either. I'm more agnostic on omnivopterids. Certainly a little higher up the tree (word-play intended) you start seeing early birds aquire characters that are specializations for abroreality, so it doesn't seem to take too long once birds really get "going" in their radiation.

You have to go quite a way up the tree (word-play still intended) before you find a fully reversed hallux. This character appears quite late in avian evolution, in fairly derived euornitheans and avisaurid enantiornitheans. Confuciusornithids and a bunch of enantiornitheans (e.g., _Sinornis_) show a medially (or slightly posteromedially) directed hallux, which might have been used for grasping branches without being specialized for it.

Then again, a large proportion of known Mesozoic birds appear to have been shorebirds, so a specialized perching pes may not have been too necessary. For example, _Gansus_ has a fully reversed hallux, but the hallux is also rather short. One possible explanation is that _Gansus_ evolved from arboreal birds, but the hallux was secondarily shortened in the line leading to _Gansus_.

Jim Cunningham wrote:

However, goats do not habitually climb trees and they show no specific adaptations to either scansoriality or arboreality.

And I never meant to imply that they did. I was making the point that you don't have to have specific adaptations to either scansoriality or arboreality in order to get into the trees...... :-)

Didn't mean to single you out, Jim. :-) I agree with you. I once climbed a tree quite easily. Falling out was even easier!

For microraptorans, _Archaeopteryx_ and certain other basal birds, if they did habitually take to the trees we might expect to see arboreal adaptations. It's arguable whether changes to phalangeal proportions, claw curvature, etc qualify as arboreal adaptations. A specialized perching pes, however, is proof positive of arboreality. As the hallux shifted all the way down on the foot, and became larger and fully reversed, it becomes clear that the pes was used for grasping. But in fossil taxa that have one or more of these characters incipiently expressed, then the evidence for arboreality is more ambiguous.



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