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Re: Segnosaurs ejected from AVES



On Tue, Jan 29, 2002 at 11:41:29PM -0500, Dinogeorge@aol.com sent:
> In a message dated 1/29/02 11:02:59 PM EST, qilongia@yahoo.com writes:
> 
> << There are about 20 different features that unite segnosaurs and 
> oviraptorosaurs. >>
> 
> In two runs of 100 flips of a coin, there will be about 50% matches. Does 
> this mean that the two runs are not independent? 

No, it doesn't, in the sense of being *flipped*.

In the sense of being the same kind of thing, the same *made* thing,
coins are certainly not independent from each other in their
characteristics.

> Likewise, if two theropod lineages extend far enough, they will
> acquire a number of the same bistate characters independently (carpals
> fused into a "semilunate" being one such).  Does this mean they're
> related?

You can only get that outcome if the genetic choice spaces are very,
very similar over long spans of time; if the 'flipping' doesn't happen
at the same rate, if the consequences of one change constrain another
(and we can be certain that in some cases this is what happens), the
necessary parrallism of events in your analogy is destroyed.

You seem to be arguing for a general strong constraint on derived
characters based on body plans, and I have real trouble wtih that, since
that theropod body plan has produced penguins and pelicans as well as
carnosaurs and segnosaurs.

Characters alone aren't sufficent, but developmental sequences of
characters ought to be.  Has anyone used stratigraphic information in a
cladogram?  (Just in terms of 'preceeds'; stratigraphic position doesn't
correlate all that well to phylogenetic position.)

-- 
graydon@dsl.ca   |  Hige sceal þe heardra, heorte þe cenre,
                 |  mod sceal þe mare þe ure maegen lytlað.
                 |   -- Beorhtwold, "The Battle of Maldon"