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Re: Digit homology
Original Message by Luis Rey Sunday, 10. November 2002 19:21
> Given that tetanuran
> theropods exhibit only three digits and that a shift in the axis of
> condensation from digit 4 to 3 has been suggested for
> some vertebrate groups (frogs and salamanders), it could be that all
> tetanurans have shifted the axis of condensation.
> How can the axis has passed through embryological digit 4 when the
> animals only have 3 digit?
And what about the finding that the axis doesn't pass through a finger but
through the distal carpals from V (or VI...) to I, while all metacarpals and
fingers form postaxially = distolaterally to the axis (with another axis,
apparently from the radius instead of the ulna, ending in the praepollex)? I
have never seen this mentioned in Feduccia's papers or answers to them, but
constantly in illustrations of the evolution of hands from fins. Or am I
talking about another axis altogether?
> Frame shifts can occur, apparently without severe pleiotropic effects,
> as is demonstrated by vertebral counts in some sauropodomorph dinosaurs
> (where there are only two sacrals but whether the sacrals are derived from
> caudal or dorsal vertebrae differs between genera: this is a new
> discovery reported at the 2002 SVPCA meeting).
Galton has constantly been publishing on this since 2000.