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Re: Archaeopteryx Pes
Allan Smith wrote-
I have found several skeletal reconstructions of Archaeopteryx with digit
retracted like in dromaeosaurs. Is this an accepted position or just one
theory? I have four casts of archy and none of them show this retraction.
I assume you mean digit II, which is the "sickle claw" of dromaeosaurs and
some other paravians. The idea was originally proposed by Paul (1988).
Elzanowski and Pasko (1999) determined that Paul had the phalanges upside
down, so there was no possibility of retracting the digit.
Actually, Jacques Gauthier was the first to propose a
hyperextensible digit II in Archaeopteryx (in his 1986 theropod
phylogeny paper) and observation of the Eichstatt specimen (or casts
like the ones I've seen) makes it pretty clear he's right: the end of
the first phalanx in digit II has a distinctly enlarged articular
surface that would have allowed the toe to retract. It is much larger
than the other joints, and like the rest of the skeleton the toes are
very well-articulated, as far as I can tell. In Archaeopteryx, the
second toe is almost always more extended than the others; this is an
observation of Greg Paul's that supports Gauthier's conclusion.
Something very similar seems to have been going on in Confuciusornis,
Sereno I think was the first to note that. Presumably this kept the
digit off the ground and therefore sharp for piercing wood or flesh,
as in cats. The advantage over cats is that the other toes aren't
retracted so the claws can still be used on the ground for traction.