fossils as roots

[Una Smith]

Hilary Davis wrote:

>I'd like to hear some opinions on the use of fossils to root a cladogram
>or tree.  Is this a valid technique given the possibility that a fossil
>assemblage for a particular extant group may not be complete?

I work on fossils, so wish I could to do this.  However, I do not think
it is a valid technique.  It is essentially the same as picking a given
extant plant group as the outgroup on the assumption that the group is
"primitive" or "basal".  A fossil group might or might not be primitive.
Primitiveness depends on the context, the choice of taxa included in the
analysis.

Computer simulations aside, we cannot expect an assemblage to be complete.
It doesn't matter whether the assemblage is fossil or extant.


        Una Smith               una.smith at yale.edu

        Department of Ecology and Evolutionary Biology
        Yale University
        New Haven, CT  06520-8106

        http://pantheon.yale.edu/~una/