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Re: Hoatzin & Archaeopteryx

Amtoine Grant wrote-

> Just thinking, has anybody compared the skeletons of Archaeopteryx.
> Especially with the controversy regarding manual digits 1,2,3 & 4 in
> theropods & extant birds, this could prove interesting.

Yes, many people have.  Most recently, Senter and Robins (2003)-
http://dml.cmnh.org/2003Dec/msg00547.html .  It's impossible to tell what
the embyonic identity of a digit is from adult remains, so Archaeopteryx
fossils don't shed any light on the homeotic shift's timing.

> I've been
> wondering if the Hoatzin could be a late-surviving Archaeopteryid[to
> coin a phrase] - which would somewhat explain it being the only extant
> member of it's family or an example of regressive evolution, as has
> been suggested.

It's not the only living bird with manual claws, far from it.  Indeed, natal
anseriformes, occassional specimens of natal Circus, natal Otus, Rallus, and
adult Corygyps are all known to have nguals on digits I and II just like the
hoatzin.  Besides, the rest of the hoatzin's characters are FAR more derived
than Archaeopteryx, or even enantiornithines or yanornithids (which have the
same number of claws as the hoatzin).
Fisher, H. I. 1940. The Occurrence of Vestigial Claws on the Wings of Birds.
American Midland Naturalist 23:234-243.

Mickey Mortimer
Undergraduate, Earth and Space Sciences
University of Washington
The Theropod Database - http://students.washington.edu/eoraptor/Home.html