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RE: Defending grades (Was: Re: Archaeopteryx (rant))

Quoting grossber <grossber@grinnell.edu>:

> All my original post was saying is that ancestral line cannot be the only 
> defining characteristic of a cladogram.

It's not.  This seems to be a common misapprehension.  Saying that birds are a 
part of Dinosauria (since they are descended from the common ancestor of all 
Dinosauria) does not make them not birds.  The distinctness of birds is still 
maintained by the recognition of a clade Aves.

Phenotypic classification (e.g. scaly all over = "reptile") sort of works OK 
if you just look at the animals we have around today, but it's ridiculous to 
expect all the missing species in between to fit into these neat categories.  
If we want a system that can accommodate all life that has ever lived, past 
and present, we're going to need a different system.

Personally, I regret that the name Reptilia ('crawly things') was retained for 
the clade including lizards, snakes, tuataras, turtles, crocs, and birds.  But 
one of the many drawbacks to Linnaean taxonomy is that recognizing two 
coordinate "classes" Reptilia and Aves prevents one from recognizing a clade 
like Maniraptora, or Tetanurae (inclusive of birds), unless you want to allow 
messy, overlapping classificatory systems.  In PT, you can recognize all those 
various clades, because you never have to draw a line below which X is classed 
as a "reptile" and above which Y is classed as a "bird/avian".

Nick Pharris
Department of Linguistics
University of Michigan