fossils as roots

[Ken Kinman]

     Using fossils as an informative root depends mostly on what group
of organisms are being analyzed, and the quality and quantity of it's
known fossil record.  There is probably a whole continuum of fossil
"usefulness", from (1) virtually worthless (bacteria for instance, where
genetic data are the most useful characters) to (2) crucial (the
mammalian fossil record is extremely important to our understanding of
that group's evolution).  And between such extremes, fossil information
can be more or less useful depending on what characters are being used
and how well they show up in the fossil record.
     Rooting in cladistic analysis can be a tricky business, especially
when it comes to fossils.  Even when one is dealing only with extant
forms, misrooting can have grave consequences, and Carl Woese's
misrooting of the tree of life (once it is fully exposed) will become a
prime example of how such misrootings can lead one to false conclusions.
But that story is still unfolding and mired in debate.  Probably the
most important lesson to be learned from it, will be that one should try
experimenting with a number of different rootings before becoming too
attached to any one in particular, whether they are fossil or extant.
                              Sincerely, Ken Kinman
********************************************************
>Date:         Wed, 3 Mar 1999 07:38:36 -0700
>Reply-To:     Hilary Davis <davish at HOLLY.COLOSTATE.EDU>
>From:         Hilary Davis <davish at HOLLY.COLOSTATE.EDU>
>Subject:      fossils as roots
>To:           Multiple recipients of list TAXACOM
<TAXACOM at cmsa.Berkeley.EDU>
>
>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?
>
>Thanks,
>Hilary Davis
>Colorado State University
>Department of Biology
>davish at holly.colostate.edu

______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com