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Re: up!up!up!and away!
On Sun, 21 Mar 1999 Philidor11@aol.com wrote:
> Is that all or most of the characters that keep it in the clade? This does
> raise the question of how many characteristics an animal has to be 'missing'
> to be outside the clade. Is there a general principle that says an animal in
> direct line of descent (probably) is so different from prior examples that a
> new clade is needed?
OK, one more time. A species can NEVER be outside a clade of which its
ancestors were members. That is because clades are defined in terms of
patterns of descent, not by characters. Characters and character states
are the tools we use to determine who shares a common ancestor with whom.
In practice, one will often hear statements like "this species has
character X, and is therefore a member of clade A."
But this is really a shorthand for "this species has character X, and is
therefore most likely descended from the most recent common ancestor of
species P and Q, and would thereby be a member of clade A."
(if one is talking about a node-based clade)
As to whether there are any hard-and-fast rules about when a new clade is
named, no, there aren't any, which is what leads to problems like the
recent confusion over what should be called a "bird".
Pacific Lutheran University
Tacoma, WA 98447