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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.
Vertebrate Paleontologist
Dept. of Geology
University of Maryland
College Park, MD  20742
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Fax: 301-314-9661