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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.