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Re: Heterodontosaurid with protofeathers

On Thu, Mar 19, 2009 at 3:43 AM, Tim Williams <tijawi@yahoo.com> wrote:
> 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.

Yes, you could introduce a "self-destruction" device in a
introduction. But it could be made with any definition, not only
branch or node-based ones.

"Avifilopluma" refers to the clade stemming from the first panavian
[Panaves Gauthier & de Queiroz 2001: the most inclusive clade
containing Aves (Vultur gryphus Linnaeus 1758) but not Crocodylia
(Crocodylus niloticus Laurenti 1768)] with feathers homologous
(synapomorphic) with those of Aves (Vultur gryphus Linnaeus 1758).
"Feathers" here refers to hollow-based, filamentous, epidermal
appendages produced by follicles. (Gauthier & de Queiroz 2001)

Avipluma (1st theropod with Vultur gryphus' hollow-based, branched,
filamentous epidermal appendages [= feathers])

Alternatively one could use a *set* of apomorphies.

But it is not a stability, just a condition to not use the term in an
unwanted way.

> the entire concept of "Dinosauria" would be meaningless anyway, so the taxon 
> would
> collapse.

Yeah, it would collapse. But collapse is not a kind of stability.

Someday I will test the stability of some definitions - cladistic and
non-cladistic ones - in a retrospective manner. Let's say, if we apply
the _Passer domesticus_ + _Triceratops horridus_ definition of
Dinosauria back into 1889 how would be their tree topology (a tree
constructed with phylogenetic analysis and the characters state as
known at that time)?


Roberto Takata