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Re: Heterodontosaurid with protofeathers

On Thu, Mar 19, 2009 at 12:26 AM, Tim Williams <tijawi@yahoo.com> wrote:
> Yes, that's true.  Wow.  This highlights some of the perils associated with 
> apomorphy-based definitions: (1) establishing
> homology; (2) having the content of an apomorphy-based clade expand 
> dramatically when the phylogenetic bracket for the
> particular apomorphy expands.

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.

Lets say that we discover that mammals are more closely related to
birds than ornithischian are, a lot of thing will be included within
Dinosauria based on node definition - with a theropod and an
ornithischian species as specifiers.

No strict content or topological stability is allowed because a
phylogeny is a scientific hypothesis, and scientific hypotheses are
subjected to refutation. The only stability that we could have is a
definitional stability: but it doesn't matter if it is apomorphy,
branch or node-based definition.


Roberto Takata