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Re: Heterodontosaurid with protofeathers



Before we get too hasty...let's not forget the alternative explanation that heterodontosaurs may actually be secondarily flightless birds that are not dinosaurs, only examples of convergent evolution with dinosaurs....


Phew...I couldn't even _type_ that with a straight face!


Scott Hartman Science Director Wyoming Dinosaur Center 110 Carter Ranch Rd. Thermopolis, WY 82443 (800) 455-3466 ext. 230 Cell: (307) 921-8333

www.skeletaldrawing.com

-----Original Message-----
From: T. Michael Keesey <keesey@gmail.com>
To: dinosaur@usc.edu
Sent: Thu, 19 Mar 2009 9:27 am
Subject: Re: Heterodontosaurid with protofeathers






On Wed, Mar 18, 2009 at 11:43 PM, Tim Williams <tijawi@yahoo.com> wrote:

Well, the dramatic content expansion is not a peril associated
exclusively to apomorphy-based definitions. Any phylogeny-based
definition: apomorphy, branch or node are subjected to such events.

Branch- and node-based definitions can be defined such that they
preclude
these kind of situations from arising. ÂFor example, a node-based definition for
a taxon could be framed such as "the least inclusive clade containing A and B,
but not C, D or E". ÂSo if C or D or E fall inside a clade that has A and B as
internal specifiers, then the taxon is no longer viable.

For stem-based definitions you could say "The most inclusive clade
including A
but not B, or W or X or Y or Z". Â
In this case the taxon would persist, but the
multiple external specifiers helps limit the content of the taxon if a huge
shift in topology were to occur.


Actually, the apomorphy-based definition of _Avifilopluma_ is
self-destructing (or, to be more precise, auto-synonymizing).
"'Avifilopluma' is defined as the clade stemming from the first
*panavian* with feathers homologous (synapomorphic) with those of Aves
(Vultur gryphus Linnaeus 1758). 'Feathers' here refers to
hollow-based, filamentous, epidermal appendages produced by
follicles." So if the trait extend beyond _Panaves_ (=pan-Aves, i.e.,
the avian total group), then it becomes a junior synonym of that name.
Of course, that doesn't affect the present situation, but it shows
that such possibilities are not limited to node- and branch-based
definitions.

I'm not sure I see a problem that needs fixing here, though. What else
would the name "Avifilopluma" refer to? It doesn't make any sense to
give that particular name a node- or branch-based definition. And if
you don't have a use for the name ... don't use it!
--
T. Michael Keesey
Technical Consultant and Developer, Internet Technologies
Glendale, California