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Re: Dumb Names (Prolacertiformes?)





Tim,
     Obviously a lot of people disagree with you (that Prolacertiformes is
holophyletic, i.e. strictly moonophyletic).  It's probably paraphyletic at
best, and polyphyletic at worse (depending on what you include).
     Thecodontiformes on the other hand is very clearly a natural
paraphyletic group, which gave rise to three ex-groups: (1)
Pterosauriformes; (2) Crocodyliformes; and (3) the dinosaur-bird clade (two
orders and a marker).    If Feduccia and friends want to put the bird marker
next to some family of Thecodontiformes they are free to do so, and
apparently they have decided on Longisquamidae (at least for now).   I have
always shown birds arising from Saurischiformes, and continue to place the
birds as sister group to Family Dromaeosauridae (sensu lato).
     I definitely do not approve of wastebaskets, i.e. polyphyletic groups,
especially when they are masquerading as paraphyletic (or worse yet as
holophyletic).  Polyphyletic groups should be discarded.  Paraphyletic
groups should be minimized (but not totally eliminated) and clearly marked
as such.  Prolacertiformes could be anything from polyphyletic to
holophyletic, and because of this uncertainty, it is therefore less
desirable than Thecodontiformes (which is definitely paraphyletic, labelled
as such, and contains markers for its exgroups).
      Politely returning the soapbox to you,
                                Ken :-)
*********************************************************
From: "Tim Williams" <twilliams_alpha@hotmail.com>
To: kinman@hotmail.com, dinosaur@usc.edu
Subject: Re: Dumb Names (Prolacertiformes?)
Date: Mon, 26 Mar 2001 11:05:08 -0600


Ken Kinman wrote:

[snip]
     Until it is sorted out (which could take many years), I continue to
recognize such groups as individual families (hopefully clades) of Order
Thecodontiformes, including:
Protorosauridae, Prolacertidae, Megalancosauridae, Tanystropheidae,
Sharovipterygidae, Longisquamidae, along with Doswelliidae,
Trilophosauridae, Rhynchosauridae, and the choristodere families.
[snip]
No need for a formal name Prolacertiformes, which is
obviously controversial, confusing, and an unnecessary name.

And "Thecodontiformes" isn't controversial, confusing and unnecessary???? At least the Prolacertiformes are monophyletic.

One of the problems with retaining even a vestige of the old concept of
"Thecodontia" is that it gets mistaken for a valid, natural grouping.
Example:

"So, if birds didn't evolve from theropod dinosaurs, what did they evolve
from?"
"From the thecodonts.  They were a diverse and successful group at the base
of the Archosauria, and included some obvious gliding and arboreal forms."
"Yes, but which *particular* group of thecodonts?"
"Oh, that's not important.  The thecodonts were so diverse that one of them
is sure to be related to the origin of birds."
" !!!??? "

Like the Condylarthra of old, the "Thecodontia" (your "Thecodontiformes")
is part wellspring and part wastebasket.  Either way, it's a dog's
breakfast.  Rather than providing elucidation and clarification, it just
confuses and obscures relationships between groups.


Tim

(Clambering up on my soapbox too.)

------------------------------------------------------------

Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163

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