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Re: Heterodontosaurid with protofeathers



They may also be dinosaur-mimicking mammals or ornithischian- mimicking birds... In any case those must be obviously collagen fibers... I have always been troubled by all those collagen fibers surrounding the Confuciusornis specimens...

Stopping the comedy for a second...I can only say... I've been sitting quietly all these years with my pet theory that fuzz is a basal characteristic of Dinosauria . It went doing the rounds up and down (mostly battered by adverse weather)... and guess what it is coming 360 degrees back again to the start?

And thinking that I did Eoraptor partly covered in fuzz 10 or 12 years ago... Who knows... that could be the next one!


On 19 Mar 2009, at 18:31, dinoboygraphics@aol.com wrote:

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. For 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". So 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".
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






Luis Rey

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