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Re: the origin of the pteroid



>
>
>   The os centrale is usually inside the wrist, part of the second level of
> carpals. It's emmigration external to the mobile wrist structure and loss
> of the rest of the middle carpals has not been demonstrated, even by
> Peters, rather than a "just-so" story to explain possible
> pterosaur-"protorosaur" homologies. No one has considered either of two
> possibilities, to my knowledge: 1) the pteroid represents a modified
> tendon, as in the flexor bone found in various talpids and chrysochlorids,
> which features as ossification of the flexor tendon of the wrist, or 2)
> that this represents a possible homology to one of the digits. If birds
> can undergo a frameshift, as has been theorized, so may too had pterosaurs
> simply translated identity from the pollex onto the second finger. Thus,
> the digits would be pteroid-II-III-IV-V, not I-II-III-IV-X. These are
> balanced, I think, hypotheses. Other theories include possible modified
> carpals.

Unwin et al. 1996 indicated that the pteroid was a true bone. Not an ossified 
tendon.
Peters 2002 showed that all of the distal carpals are in place in 
Eudimorphodon, Anurognathus, Jeholopterus and other primitive pterosaurs. 
Likewise the radiale, ulnare and pisiform are in place. Two bones are lacking, 
the middle carpals.
Two bones that were never there before suddenly appear, the preaxial carpal and 
pteroid.

Is this is the Superman/Clark Kent theory, in which the two are never seen in 
the same room at the same time together?

Or just parsimony?

David Peters
St. Louis