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SV: Shaking up the bird family tree
The problem here is that to argue that flight is lost, you must have
1) a single gaining of flight, 2) loss of flight in ostriches, 3) loss
of flight in rheas, and 4) loss of flight in the cassowary/kiwi/emu
clade. This is more steps than a simpler explanation in which tinamous
gained flight after the whole lost it. A tad more parsimonious, rather.
Jaime A. Headden
Being parsimonious does not necessarily mean the same as being right.
The problem here is that we know that cases of bird lineages becoming
flightless are extremely common (I could cite a couple of hundred
instances), while we know only "a single gaining of flight" somewhere
back in the Jurassic.
Using the same argument I could just as easily argue that several rail
taxa are primitively flightless since they consist of one flighted and
several flightless species.
Since Steadman has actually worked a lot on flightless rails he should
really know better.
It is interesting to note that the location of hoatzin and seriemas is
still rather shaky.