Re: Dinosaurian Class (was: DROMAEOSAURS AND OVIRAPTOROSAURS ....)

[chris brochu <cbrochu@fmppr.fmnh.org>]

>Of course I don't expect any of this to really take off, but as a concept
>I feel it could work (then again, communism is a wonderful concept that
>hasn't worked well in practice).  Would this make reptiles paraphyletic?
>Yes and here is a big subject not lightly delved into.  What non-reptilian
>sauropsids are there?  As far as I can tell, only mesosaurs (see T. Mike
>Keesey's wonderful site which has all the latest in systematics at
><http://www.gl.umbc.edu/~tkeese1/dinosaur>) If mesosaurs are the only
>non-reptilian sauropsids, would it not be better to simply drop Reptilia
>and its commonly associated characteristics (not always appropriately
>associated characteristics at that) in favor of Sauropsida in cladistic
>use?  Then we could still have our paraphyletic Class: Reptilia, Class:
>Pelycosauria, Class: Neosynapsida (incl. mammals) and Class: Archosauria
>(or Archosauriformes if you prefer) while maintaining no descrepincy with
>cladistics.
>

Actually, most of us hard-core cladists still refer to grades as well -
it's not just for the lay.  However, we draw a distinction between
recognizing a grade and actually erecting a taxon around it.  "Pelycosaur"
is a valid adjective, describing a basal synapsid lacking certain derived
character states, but the noun "Pelycosauria" is no longer viable.

An example used by de Quieroz several years ago works well here:  consider
a family of peasants.  Their family name might be Bauer, which is German
for "peasant."  Suppose someone down the line becomes an accountant - he or
she is no longer a peasant, but would still use the name Bauer.  By the
same token, the earliest known synapsids were of "pelycosaurian grade."
Modern synapsids are still members of Synapsida, but we no longer refer to
them as "pelycosaurs."  One refers to an individual, the other to a class
(in the philosophical rather than Linnean sense) of objects.  Monophyletic
taxa, strictly speaking, are not just assemblages of member species, but
individuals in and of themselves.

As for "dropping Reptilia:"  Unfortunately, priority is priority, and even
in the Linnean system appropriateness is not a valid reason for eliminating
or modifying a group name.  So your suggestion would actually cause great
discrepancy with the modern phylogenetic system.  In hindsight, it might
have been best to not redefine Reptilia as a monophyletic group - but it's
done.


chris


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Christopher Brochu

Postdoctoral Research Scientist
Department of Geology
Field Museum of Natural History
Lake Shore Drive at Roosevelt Road
Chicago, IL  60605  USA

phone:  312-922-9410, ext. 469
fax:  312-922-9566

cbrochu@fmppr.fmnh.org