One more damn time (was Re: More phylogenetic taxonom...)

["Thomas R. Holtz, Jr." <th81@umail.umd.edu>]

At 07:30 PM 6/13/97 -0400, Dinogeoge wrote:
><< (Incidentally, the node joining Sauropsida and Synapsida is Amniota.  The
> (as yet unknown or unrecognized) most immediate common ancestor of reptiles
> and mammals was an amniote (by definition) but neither a sauropsid nor a
> synapsid (also by definition).) >>
>
>This, by the way, makes the most immediate common ancestor of reptiles and
>mammals a paraphyletic taxon, since it doesn't include >any< of its
>decendants (let alone >all< of its descendants). You can't get away from
>paraphyly...

Unlike George, hopefully the rest of you remember the numerous times in the
past where we have pointed out that species (under most definitions) are a
distinct type of taxon, and many of them would indeed be paraphyletic.  Yes,
the SPECIES which was the most immediate common ancestor of reptiles and
mammals would be paraphyletic, but no higher taxon (except for its genus,
but this has simply to do with the tradition of not leaving a species name
as a single word).

A few species definitions require monophyly, so that as soon as a species
diverges, it becomes two new species, even if one of the descendants is not
morphologically, behaviorally, or genetically distinct from the ancestor.
I, and many other evolutionary biologists, do not except this type of
species definition.

Hope this clears things up.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661