Well we know flight evolved three separate times - pteradactyls, birds and
bats, so why not the reverse?
Regards,
Chris
On Mon, Sep 8, 2008 at 3:57 PM, John Leonard <>wrote:
> There's always a temptation for people to invoke Occam's Razor and
> decide that the simplest explanation is what happened (here, that
> flightlessness evolved once in the common ancestor). However, time is
> very long and we have limited knowledge of the different speciation
> events that took place. So, it appears, the simplest explanation is
> not the case!
>
> John Leonard
>
> 2008/9/8 Andrew Taylor <>:
> > "Large flightless birds of the southern continents - African ostriches,
> > Australian emus and cassowaries, South American rheas and the New
> Zealand
> > kiwi - do not share a common flightless ancestor as once believed."
> >
> > More at:
> > http://www.sciencedaily.com/releases/2008/09/080903172152.htm
> >
> > The PNAS paper is here (abstract appended):
> >
> http://www.pnas.org/content/early/2008/09/02/0803242105.abstract?sid=bac941fc-cf09-4fe2-8e2b-18a15bcb3a97
> >
> > Andrew
> >
> >
> > Phylogenomic evidence for multiple losses of flight in ratite birds
> > Harshman et al.
> >
> > Ratites (ostriches, emus, rheas, cassowaries, and kiwis) are large,
> > flightless birds that have long fascinated biologists. Their current
> > distribution on isolated southern land masses is believed to reflect the
> > breakup of the paleocontinent of Gondwana. The prevailing view is that
> > ratites are monophyletic, with the flighted tinamous as their sister
> > group, suggesting a single loss of flight in the common ancestry of
> > ratites. However, phylogenetic analyses of 20 unlinked nuclear genes
> > reveal a genome-wide signal that unequivocally places tinamous within
> > ratites, making ratites polyphyletic and suggesting multiple losses of
> > flight. Phenomena that can mislead phylogenetic analyses, including long
> > branch attraction, base compositional bias, discordance between gene
> trees
> > and species trees, and sequence alignment errors, have been eliminated
> > as explanations for this result. The most plausible hypothesis requires
> > at least three losses of flight and explains the many morphological
> > and behavioral similarities among ratites by parallel or convergent
> > evolution. Finally, this phylogeny demands fundamental reconsideration
> > of proposals that relate ratite evolution to continental drift.
> >
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>
>
> --
> John Leonard
> Canberra
> Australia
> www.jleonard.net
> ===============================
> www.birding-aus.org
> birding-aus.blogspot.com
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