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
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