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Re: Phylogenetic Taxonomy [was Re: Cladistic Massive Retaliation]



[ I've suppressed some cladistics discussions that otherwise would
  have continued on the list -- after all this is a dinosaur list not
  a cladistics list!  I'm letting this through because it focuses on a
  basic point rather than a finer detail.  Boy I can't wait till I can
  stop making these decisions!  In the mean time you can make my life
  easier (and I'm sure you all have that as a goal :-) by trying to
  make sure all comments to the list are tied to dinosaurs.  Thanks. 
  -- MR ]

At 12:30 PM 11/23/96 -0500, Stan Friesen  wrote:

>From: "Jonathan R. Wagner" <znc14@ttacs1.ttu.edu>
>
> >    Such as?  What monolphyletic group of animals cannot be expressed
> > as a common ancestor and its decendants?
>
>A direct ancestor-descendant pair is not expressable in the normal
>cladistic approach.  The ancestor is instead represented as a sister-
>species of the descendent

Ummm, not quite.  The following will sound very familiar to long-time
readers on the net, & I suppose I will have to keep reposting this once or
twice a year whenever it comes up...

It is possible to express an ancestor-descendant pair in cladistics.  An
ancestor (A) would be the sister group to the descendant clade (D) in terms
of character states (have unique synapomorphies with D but none on its own:
a metataxon), A would occur earlier in time than all of D, and (it would be
nice) within the geographic range of D.

A cladogram is NOT the be-all and end-all of a phylogenetic analysis.  It is
the graphical representation of the most parsimonious distribution of
derived character states within a data matrix.  One can turn a cladogram
into a phylogram if one chooses by mapping the cladogram onto time and
including potential ancestor-descendant pairings onto the tree.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661

"To trace that life in its manifold changes through past ages to the present
is a ... difficult task, but one from which modern science does not shrink.
In this wide field, every earnest effort will meet with some degree of
success; every year will add new and important facts; and every generation
will bring to light some law, in accordance with which ancient life has been
changed into life as we see it around us to-day."
        --O.C. Marsh, Vice Presidential Address, AAAS, August 30, 1877