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Re: Dinosaur Discussion List Dictionary

In a message dated 95-10-24 13:34:07 EDT, rowe@lepomis.psych.upenn.edu
(Mickey Rowe) writes:

>> OUTGROUP--n. A clade considered primitive to a group of organisms in
>> a cladistic analysis of that group.
>I think this one is downright wrong because of the inclusion of the
>word "primitive".  While it's true that you look for primitive
>character states by comparisons with outgroups, it is a fallacy to
>presume that the character state retained by an outgroup is the
>primitive character state.  An outgroup is just a clade whose most
>recent common ancestor with the ingroup lived before the common
>ancestor that defines the ingroup as a monophyletic clade. 

I don't say that the characters and character states are primitive in the
outgroup, just that the outgroup itself is. Your last sentence above is
equivalent to my definition, but may be a more straightforward way of putting
it. The assumption in outgroup analysis is that the outgroup is primitive--an
assumption that comes from outside the analysis itself (lest our reasoning
become circular). By the way, in my humble opinion, poor choice of outgroups
seems to have generated lots of errors in dinosaur cladisitics over the past
few years.