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Re: Re: A few more...

>In a message dated 95-09-29 13:20:48 EDT, Thomas_R_HOLTZ@umail.umd.edu (th81)
>>Much in the way that the hoatzin "magically regained" functional unguals?
>>Reversals happen.
>Birds never really "lost" functional unguals, since these are expressed in
>most avian embryos. Hoatzin juveniles retain them until adulthood, when, as
>in all good birds, they are subsumed into the wing.

Expression in the egg of unguals are NONfunctional, whereas the juvenile
hoatzins demonstrate a reversal to a condition in which the unguals are
present and used after hatching.  This is a reversal, and it did happen.  It
also suggests mechanisms whereby the metatarsals of therizinosauroids and
sauropods might, in their own ways, revert to an ancestral (in the former
case) or unique (in the latter) state.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist
Dept. of Geology
University of Maryland
College Park, MD  20742
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Fax: 301-314-9661