Re: Amphibians - the comeback kings of evolution

["T. Michael Keesey" <keesey@gmail.com>]

On 1/9/07, Dann Pigdon <dannj@alphalink.com.au> wrote:
> >>
> >> Is that a right use of term "common"?
> >
> > It's confusing, but I'm pretty sure they mean "common" respectively,
> > i.e., an ancestor common to all frogs and toads, an ancestor common to
> > all salamanders, and an ancestor common to all caecilians. Not three
> > ancestors common to all three extant groups. Poor wording, it seems to
> > me.
>
> Or maybe the three ancestors common to extant amphibians as a whole group.

Well, there are a lot more than three common ancestors for living
amphibians: there's the most recent common ancestor, the MRCA's
immediate ancestor, the immediate ancestor of the immediate ancestor
of the MRCA ... back to the MRCA with amniotes, the MRCA with
lungfish, with coelacanths, with ray-finned fish ... on back to the
first organism.

I think it makes much more sense that, since they are talking about
three clades, they are talking respectively about ancestors of each of
the three clades. The word "common" is not only superfluous but
confusing in this case.
--
T. Michael Keesey
The Dinosauricon: http://dino.lm.com
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