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Re: Avian flight stroke origin



Jason Brougham <jaseb@amnh.org> wrote:

> That may be, but Greg Paul never actually depicted Archaeopteryx climbing
> like a Hoatzin, did he? When he depicts Archaeopteryx in a tree, like in
> Figure 9-3, page 212, of Predatory dinosaurs of the World, he shows it
> standing on a  limb like a Chachalaca, and I think this is a conservative
> depiction that stands up to everything we've learned about Archaeopteryx
> since.


I disagree.  Chachalacas have a perching pes.  Do a Google Images
search for 'Chachalaca' and you'll get photos galore that show a
chachalaca in a tree with its large, incumbent hallux wrapped around a
tree limb, in opposition to the front toes.


http://www.naturephoto-cz.com/grey-headed-chachalaca:ortalis-cinereiceps-photo-8051.html

http://www.fredmiranda.com/forum/topic/787667

etc etc


Here's one thing that we've learned about _Archaeopteryx_: it couldn't
perch.  The hallux was relatively short, positioned relatively high on
the metatarsus compared to modern avians, and not at all reversed.  So
putting _Archaeopteryx_ out on a limb chachalaca-style is... well,
going out on a limb.  IMHO, it's not a "conservative depiction" at all
to claim that a theropod with a non-reversed hallux could perch like a
modern bird (in this case, a cracid).


Granted, paravians do tend to show some changes to the hallux compared
to the primitive theropod condition, including in the more distal
location of metatarsal I  - this was discussed by Xu and Zhang (2005)
as part of their description of _Pedopenna_.  But this more distal
hallux (also seen in microraptorines and velociraptorines) is a far
cry from what we see in modern birds, and even in many Cretaceous
non-euornithean birds (including sapeornithids/omnivoropterygids and
enantiornitheans) that have a ped adapted for opposable grasping







Cheers

Tim