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Non-amniote sarcopterygians


Seeing the current spate of gradistic vs. cladistic nomenclature on the DML,
I'm reminded of the saying "the more things change, the more they stay the
same"...  (Go to the list archives if you wonder why.  I'm not going to
bother to post any messages in the current go round, since I've said it all
before again and again...).

However, for those interested in new analyses and studies, I believe the
following has not yet been posted to the list:

RUTA, M., M.I. COATES and D.L.J. QUICKE. 2003. Early tetrapod relationships
revisited. Biological Reviews 78: 251-345.

A 94 page long study of amphibian-grade sarcopterygian relationships.  Very
detailed work, with 90 OTUs and 319 characters.  In their results, the
classic -stegas (Venta-, Acantho-, Ichthyo-) as well as Tulerpeton, the
colosteids, Crassigyrinus, Whatcheria, and the baphetids are the outgroups
of crown-group Tetrapoda; Eucritta is the sistertaxon to temnospondyls
(which contain Lissamphibia); embolomeres, gephryostegids, semouryiamorphs,
and a few others are outgroups to a lepospondyl+(diadectomorph + amniote)
clade (so that Diplocaulus is closer to us than it is to frogs...).

Incidentally, the authors here follow the traditions of some of the
paleoicthyological community (and some others): nearly all "traditional"
names are stem-based, with their anchor taxa being living forms.
Consequently, they use "Lissamphibia" and "Tetrapoda" more broadly than a
lot of other folks would (i.e., Eusthenopteron and Panderichthys are
stem-tetrapods; Eryops is a stem-lissamphibian).  They recognize that this
results in Triceratops being a stem-bird and Dimetrodon being a stem-mammal,
but so be it.

Needless to say (based on my published work and notes on the list), I'm
perfectly happy with restricting traditional taxon names to subclades within
the larger total clade denoted by all taxa closer to clade A than to its
closest living relatives.  (That is, I'm happy for Aves to be an arbitrarily
defined node within Maniraptora, Theropoda, Dinosauria, and so forth).  But
I give these folks credit: they are honest in respecting their taxonomic
philosophy even if it results in Desmatosuchus as a crocodile, Stegosaurus
as a bird, or Phacops as a chelicerate...

                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