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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:

>> PLESIOMORPHY--n. A character present throughout a taxon because it
>> is present in an outgroup of the taxon.
>
>I think the above definition is better suited to the word
>"symplesiomorphy", but even in that context the "because" bothers me.
>In any case, plesiomporphy is the antonym of apomorphy -- a
>plesiomorphy is a primitive character or character state (note that
>all of these terms are relative -- a state which is primitive in one
>comparison may be derived in another.  Take whiskers for example: When
>comparing primates and rodents, the presence of whiskers is the
>primitive condition because their most recent common ancestor had
>whiskers.  On the other hand, in a comparison between rodents and
>lizards the presence of whiskers is a derived condition because the
>most recent common ancestor of those two groups did *not* have them).
>
>

Right. As I just said, I tried to be minimalist in my definitions, lest we
depart from the dictionary format and embark on writing a cladistics
textbook.

G.O.