"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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