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Re: What's a plesion?
In a classification of families (within an Order), a plesion is
basically a distinctive genus which doesn't fit in well in any particular
family, but hasn't been named a separate family yet either. Sometimes
careful study, especially when additional material is found, will make it
possible to assign that genus to a particular established family or to a
separate family of its own.
The plesion is favored by many cladists who use Linnean ranks, but
don't like monotypic families. It is especially good for genera that seem
distinctive, but are poorly known. particularly when they form a cladistic
series in a stem leading up to a crown clade.
Likewise, if you are classifying the Orders within a Class, you can
classify a distinctive genus or family as a plesion, but eventually it might
be assigned its own separate Order.
P.S. When I get a cladistic series with lots of plesions (plesia?) in a
cluster, that is when I start seriously consider a paraphyletic grouping
(especially when the groups jump around a lot in different cladistic
analyses). That is why I have gone back to a broader paraphyletic
From: "aspidel" <firstname.lastname@example.org>
To: "The Dinosaur Mailing List" <email@example.com>
Subject: What's a plesion?
Date: Sun, 19 Aug 2001 15:02:38 +0200
Hi dear dino-list members,
I'm also getting slowly into cladistics and classification, it's important
to understand the evolution of dinosaurs, as I draw them.
So... What's a plesion?
Thanks in advance, friendly - LJB.
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