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Re: Re: Transitional Fossils



>In a message dated 95-10-03 14:20:41 EDT, Thomas_R_HOLTZ@umail.umd.edu (th81)
>writes:
>
>>So, stratigraphy and biogeography are not used in the cladistic analysis per
>>se, but in the transformation of the resultant cladogram into a proposed
>>phylogeny.
>
>And what happens to the phylogeny if the stratigraphic and biogeographic
>evidence are at variance with the cladogram?
>


The cladogram is constructed without stratigraphic or biogeographic data,
only with the most parsimonious distribution of derived characters states.
Since the stratigraphic and biogeographic records of many taxa (ESPECIALLY
rare large animals such as dinosaurs) are even poorer than the anatomical
record, any variance is best explained by the problems with our knowledge of
biogeography and stratigraphy.

For example, although Gorilla and Pan have VERY poor fossil records, while
hominines have a pretty good one, we don't try to derive gorillas, chimps,
and bonobos from Australopithecus, even though it appears earlier in the
record.  The distribution of derived characters show that Pan and Gorilla
diverged prior to the evolution of Australopithecus, even though this
divergence is not recorded per se in the fossil record.

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