Re: A question of Data Matrices

[chris brochu <cbrochu@fmnh.org>]

Ken Carpenter wrote:
> I use Family to denote a group of phyletically close genera (a useful term). 
> Consider: Tyrannosaurus rex, Tyrannosaurus bataar, Gorgosaurus,
> Albertosaurus, and Daspletosaurus are more closely related (the 
> Tyrannosauridae), than they are to Abelisaurus and Carnotaurus (Abelisauridae)
> and Acrocanthosaurus and Allosaurus (Allosauridae). In an analysis of these 
> nine taxa (using Ceratosaurus as an outgroup), would treating
> Carnotaurus as equally related to Tyrannosaurus rex in the data matrix as to 
> Daspletosaurus in a data matrix not be the flaw that Vermeij was
> referring to?  Might not a better phylogeny not result in analyzing 
> Tyrannosaurus rex, T. bataar, Gorgosaurus, Albertosaurus and Daspletosaurus
> separate from Allosaurus and Acrocanthosaurus and Carnotaurus and 
> Abelisaurus? Admittedly this is a very simple example, but consider the
> analysis of Holtz that used all the theropods. Would the result be better 
> with fewer parsimonious trees by analyzing different genera within the
> various "families" (or whatever term Chris would prefer) first?


There's a logical problem with what you propose.  You want to restrict
analyses to "groups of phyletically close genera," *but that presupposes
the monophyly of these groups.*  That is the specific issue a
phylogenetic analysis is designed to test - the monophyly of these
groups.  You cannot restrict an analysis to a clade unless you know, a
priori, that the clade is monophyletic in the first place, and you can't
figure that out until you've done the broader phylogenetic analysis.


chris


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Christopher A. Brochu
Department of Geology
Field Museum of Natural History
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