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Re: Digit Loss



> >Hyperphalangy is the phenomenon that the digits have more phalanges than
> >usual, not that there are more digits; this is very common in sea-living
> >tetrapods (sauropterygians, whales). The pteroid bone... hm. Might be the
> >ossified base of a tendon; it is not a metacarpal.
>
> Sorry, I should have used hyperdactyly, which is also observed in
ichthyosaurs.

...to which I wanted to add that some digits split in ichthyosaurs
(polydactyly in humans involves in AFAIK all cases a Y-shaped metacarpal),
that basal ichthyosaurs lost the thumb, and that one clade reinvented a
totally new ~digit in its place that begins at the elbow instead of at the
wrist. This is the most bizarroid fluke of developmental genetics I know.
%*) (Refs: all recent works by Ryosuke Motani; he might have something on
his website, the URL of which someone posted during the thread on sclerotic
rings.)