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Re: Sauropod ancestry?



On Tue, 18 Jul 2000, Brad M. wrote:

> > I second the query about early sauropodomorphan  pedal digits. I'm not 
> > entirely convinced that Prosauropoda is monophyletic, either
> > (although a good chunk of Prosauropoda being monophyletic seems
> > likely).
> 
> 
> Didn't some icthyosaurs re-evolve the sixth, seventh and eigth digit?

Good point. Is that a case where existing digits were copied, as in a
couple of dog breeds (Briards and some other type have two dewclaws) and
polydactylic humans, or is it a case where the actual primitive digits
were re-expressed, as has been proposed for Sauropoda? Are the digits of
Ichthyosauria homologous to those of _Ichthyostega_, or were some of the
"crown tetrapod five" digits duplicated?

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