Re: Fixing dinosaurian carnivour question

[Stanley Friesen <sarima@ix.netcom.com>]

At 10:38 PM 6/5/99 -0400, T. Mike Keesey wrote:
>On Sat, 5 Jun 1999, Stanley Friesen wrote:
>
>> The most comprehensive description of Ashlock's approach is in Part B of
>> "Principles of Systematic Zoology, 2nd Edition" by Ernst Mayr and Peter
>> Ashlock.  
>
>Could you summarize it for the rest of us non-British folk? I'm pretty
>curious.

Many university libraries have it - I first located it in the reference
section of the Biomedical library at UCLA.  [Then I ordered it online from
a british company, it was actually very easy]

A *quick* summary:

1. Derive a cladogram by any of the usual methods.

2. Annotate each internode with a measure of the change it represents (its
length)
    - the simplest, but often least useful, measure is simply the number of
synapomorphies on it.
    - a slightly more sophisticated variant is to weight the synapomorphies
inversely by their frequency on the cladogram (thus a unique synapomorphy
has the highest weight, and a highly convergent character has very low weight).
    - more sophisticated measures can be devised, as desired.

3. At any given taxonomic rank, "cut" the cladogram at those internodes
having a weighted length greater than a selected threshold - perhaps using
some statistical measure of significance or information content to
determine the threshold value.

The tree fragments produced by this cutting are the taxa to be defined.
Note, this can produce both monophyletic taxa (sensu Hennig) and
paraphyletic taxa.  And indeed it *must* produce at least one paraphyletic
taxon - the one containing the root node.


The classification of theropods on my Web page was derived in large part by
applying this method to Holtz's old "Phylogenetic Position of
Tyrannosaurids" paper, with adjustments due to later changes in the best
supported cladogram.


I have not yet had time to apply the method fully to the whole of
Dinosauria, so my other subdivisions are more subjective at this time.  In
particular, the status of Fabrosauria, Thyeophora and Marginocephalia are,
in my mind, uncertain.  For instance I am not sure the Cerapoda or the
Genasauria nodes are sufficiently weighty to separate Fabrosauria as a
first rank subtaxon of Ornithischia.

--------------
May the peace of God be with you.         sarima@ix.netcom.com