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Re: 11th specimen of Archaeopteryx



Michael Habib <MHabib@chatham.edu> wrote:

> Tim's point regarding birds nesting in abrasive plants is well taken, as is 
> Don's comments on Cycads etc.


Tim Koenig.  Not me.  There are some who call me... Tim.


> However, I still find myself
> asking the question: is there any reason we keep trying to put Archaeopteryx 
> (and close relatives) into elevated positions to begin
> with?  Don already pointed out that, at best, we simply cannot exclude some 
> arboreal roosting, etc for Archaeopteryx.  We have no
> evidence that Archie was absolutely confined to terrestrial life, but we have 
> nothing to suggest it was arboreal in any meaningful way,
> either.  As a result, I find myself a bit mystified by the continued attempts 
> at building scenarios in which Archaeopteryx spent time
> climbing about.  Yes, perhaps it did.  But one can imagine that many 
> maniraptorans could get into trees, given the right tree.
> Deinonychus could probably get into a tree, but I'm not sure the possibility 
>merits much discussion.  It's a level of behavioral specificity
> we cannot determine in fossil animals, as best I can tell.


Firstly, the study of Glen and Bennett (2007) found that certain
Mesozoic paravians (e.g., _Archaeopteyx_, _Microraptor_,
confuciusiornithids) having toe claw angles most similar to modern
"ground-foraging" birds (those that mostly forage on the ground, but
also venture into trees) more so than to exclusively terrestrial
birds.  This lends support  (albeit weak) to a 'dual-mode' ecology
among basal paravians.


Secondly, paravians tend to show certain modifications of the pes. In
basal paravians, compared to the primitive theropod condition, the
first pedal digit (hallux) becomes longer and descends further down
the metatarsus; the pedal digits become longer relative to the
metatarsus; and the penultimate phalanges become longer.
_Epidendrosaurus_ shows the most extreme condition - metatarsal I is
descended and elongated to such a degree that the hallux is at the
same level as the other toes.  The long, fully descended, reversed
hallux of birds didn't appear out of the blue: certain basal paravians
inched toward this condition by showing some elongation and distal
migration of the hallux (although reversal was still a long way off).
It is tempting to associate these pedal modifications with some form
of arboreal behavior - as many authors have done (e.g., in the
descriptions of _Microraptor_, _Pedopenna_, and _Epidendrosaurus_).
It is certainly interesting that these changes to the pedal anatomy
coincide with the appearance of large feathered wings.







Cheers

Tim