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RE: monophyletic; polyphyletic; paraphyletic

Monophyletic: a group of taxa comprised of a shared common ancestor and all of its descendants.
Paraphyletic: a group of taxa comprised of a shared common ancestor but NOT all its descendants.
Polyphyletic: a group of taxa which does not also include their common ancestor.
For example, take the tree: mammals + (turtles + (lepidosaurs + (crocodilians + birds)))
"Reptlia" as traditionally concieved is turtles, lepidosaurs, and crocodilians.  Their shared common ancestor is also considered a reptile.  However, this grouping excludes birds (because they are so radically transformed).  Thus, the traditional "Reptilia" is paraphyletic.
Reptilia as used by Gauthier (and many others now!) comprises turtles, lepidosaurs, crocodilians, birds, their common ancestor, and all of its descendants.  This grouping is a monophyletic grouping.
Some workers have proposed a taxon "Haematothermia" (the warm-bloods) for birds plus mammals, but nothing else.  Given the tree above, the common ancestor of the haematotherms would NOT also be a haematotherm, and so Haematothermia is polyphyletic.
Hope this helps.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742      
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796

-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of aspidel
Sent: Monday, August 20, 2001 4:43 PM
To: The Dinosaur Mailing List
Subject: monophyletic; polyphyletic; paraphyletic

Hi dear dino-list members,
First thanks to HP's Ken Kinman and Thomas R. Holtz Jr.'s replies.
Another question:
monophyletic: is it told about a group which is derived from a common basal species?
polyphyletic: is it told about a group which contains species sharing common features but which may derive from different basal species?
And what means paraphyletic?
Many thanks in advance, friendly - LJB.
ps: maybe I'm not clear; and excuse my bad English.