"reversal"

[Ken Kinman]

Hi Gianluca,
     A character is a reversal when it has secondarily reverted back to the
non-derived (i.e. "primitive") state.  For instance birds evolved powered
flight (a derived character) which was then apparently secondarily reversed
in some birds such as ratites.
     Considering the flightlessness of some birds as a secondary loss
(reversal) is generally viewed as being more parsimonious than the
alternative (that birds evolved powered flight more than once).
       ----  Cheers,  Ken Kinman
P.S.  The reversal of powered flight in ratites is so widely believed that
the main controversy is now whether there was a single reversal at the base
of the ratite group, or whether there were multiple reversals (independent
losses of flight) in various groups of ratites.
*****************************************
>From: Gianluca Polgar <polgar at ALFANET.IT>
>Reply-To: Gianluca Polgar <polgar at ALFANET.IT>
>To: TAXACOM at USOBI.ORG
>Subject: "reversal"
>Date: Sun, 6 Jan 2002 02:29:04 +0100
>
>Dear TAXACOM,
>
>Is there anyone who may please explain me what does it mean when a
>character is considered a "reversal", basing on other character
>distributions and on cladograms, (on most parsimonious assumptions)?
>
>Thank you very much
>
>Gianluca Polgar
>polgar at alfanet.it




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