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Re: Help with Cladistics



>Johnson through out the book launches a savage but heavily flawed (IMHO) on
>Evolution. I feel that he uses these definitions of cladistics to bolster
>his opinion that the fossil record shows no transitional species. Can
>someone give me an answer regarding cladistics and ancestoral species?
>
Although the chance of finding fossils of the population directly ancestral
to later species is very small, a cladist can recognize a potential ancestor
as one which: a) shares derived features with the hypothesized descendant;
b) lacks derived features unique to itself; c) is found stratigraphically
lower than the descendants; and (it would be nice) d) is found in a region
later inhabited by the descendants.  Any fossil which qualifies for aspects
a and b is called a "metataxon".  Thus, potential ancestors are metataxa
which occur earlier than the hypothesized descendants.

>The next request is one regarding Archaeopteryx. Using cladistics is
>Archaeopteryx regareded as a bird?

Except for those who consider Archaeopteryx to be more distantly related to
birds than other typical nonavian theropods (troodontids, etc.),
Archaeopteryx is considered a bird.  It may not be included in Aves (which
has been defined as the most recent common ancestor of all modern birds and
that ancestor's descendants), but it is still a "bird".

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
Phone:301-405-4084