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Re: Secondarily Flightless Question



Rob Gay (rob@dinodomain.com) wrote:

<I've got a question for those of you more familiar with avian phylogeny
than myself. When running a cladogram (pretty extensive), do terror birds
fall out as birds? If so (and I imagine they do), do they all clump
together (I think I know the answer here too, but I'm not too sure)? How
about ratites? If this produces a phylogeny that shows "terror birds" are
just flightless birds, along with ratites, and they lost the ability to
fly, why wouldn't postulated neoflightless dinosaurs (dromeosaurs,
enigmasaurs, etc.) show up as neoflightless dinosaurs in large analyses?>

  Rob responds to Tom's critique of the recent Czerkas book.

  I think it impossible to find a cladistic correlate to flight loss.
Either it can fly, or it does not. It's relationship to other taxa must be
used to consider loss or acquisition of flight, and such a consideration
must be mechanical. Greg Paul points out to combinations of features which
would indicate possible loss of flight, including long forleimbs, a
terrestrial body type, and large sterna, with furcular adaptations. But
the exact relationship of features has only recently come under scrutiny.
Birds today that lost flight derive from within a group of birds or
ancestral groups that possessed flight. Retention of flight-related
locomotion (as in penguins) or characters in flightless animals is largely
an observation. One thing is clear about flying animals ... it takes more
than long brachial feathers to fly, you need the arm mechanics to do it.
The arms on the "flying dromaeosaur," *Cryptovolans*, that I have observed
are too short again to have enabled much flight, maybe assisted
leaping....

  Phorusrhacoids group together on the basis of cranial and pelvic
features. Increase in size is convergent among to lineages, with one
primitive, seriama-like lineage still capable of flight, and behaviorally
in this context may have been similar. Only tinamous today among ratites
fly, but comparison to the fossil record shows that primitively, ratites
lost flight perhaps several times. That arm and sternal features vary
among ratites makes it more difficult to assess any particular trend in
flight loss about them, but maybe _among_ them.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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