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Re: Re: FW: Re: FW: Help with Cladistics
>At 1:46 AM 8/31/95, James Shields wrote:
> As long as phylogenetic analysis utilizes derived characters (via
>homology) to define the status of taxa, and as long as feathers are
>considered a synapomorphy for birds, the feathers of Archaeopteryx include
>it w/ in aves. Other fossil birds, for which there are no feathers, are
>included w/ in aves on the basis of their possession of osteological
>synapomorphies for birds.
Under cladistics, derived characters DO NOT define the status of a taxon.
The tree(s) having the most parsimonious distribution of derived characters is
the prefered phylogenetic hypothesis. Archaeopteryx is considered a bird by
certain defintions (i.e., "birds" [Avialae] = Archie & modern birds and all
descendants of the most recent common ancestor of Archie & modern birds).
Feathers remain a very weak synapomorphy of birds: since most bird outgroups
have yet to be found in a Lagerstatten environment, we have no evidence with
which to dismiss the hypothesis of feathered nonavian theropods.
Thomas R. Holtz, Jr.
Dept. of Geology
University of Maryland
College Park, MD 20742