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Re: More on Birds, dinosaurs, and digits



On Dec 1,  9:12am, Jack wrote:
> Subject: Re: More on Birds, dinosaurs, and digits
>
>
> On Mon, 1 Dec 1997 celyle@iupui.edu wrote:
>
> >
> > On Sun, 30 Nov 1997, Toby White wrote:
> >
> > > (2) The chicken pes clearly has five
> > > digits at some points in development.
> >
> (snip)
> > I've always assumed that hyperdactylics
> > are random mutations (aside from whales and icthyosaurs, etc.) yet unless
> > the Dorking's extra toe is actually it s fifth, it would appear that this
> > fluke is a norm for this breed.  Anyone know more?
> >
>
> This isn't really helpful as far as that hen goes, but hyperdactyly or
> polydactyly does seem to be random in most cases.  The only cases I can
> think of are (as you mentioned) whales and ichthyosaurs AND breeds of
> animals designed by humans.  There is a breed of goat herding dog (huge
> white animals) that have an extra toe on their hind feet.  This is
> actually a sign their being "pure-blooded".  In my experience, the extra
> digit (I believe in this animal, it is the prepollex) is usually tender.
> I don't remember off hand, but there may have been another species as well
> that has a constructed breed with an extra toe.  These along with the hen
> you write of seems to indicate to me that the hyperdactyly may be
> prevalent when humans are controlling the breeding patterns.
>
> Jack
>
>
>-- End of excerpt from Jack


Also reversals are known, certainly for guinea-pigs (cavies) (normally
tetradactyl manus) being born pentadactyl - I think this is an atavistic
reappearance of digit V.  However, I would think this is VERY unlikely
for birds due to functional constraints.

Tony Canning
tonyc@foe.co.uk