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Re: Archaeopteryx feathers and origin of flight based on 11th specimen



Mike Habib <biologyinmotion@gmail.com> wrote:

> Incidentally, another possibility to be considered: flight is basal to the 
> common ancestor of Archaeopteryx and Microraptor, and Archaeopteryx (among 
> other taxa) was secondarily flightless.


To complicate things further, it is often difficult to designate birds
as either "flighted" or "flightless".  This is true of many extant
birds that have extremely poor flight abilities.  In between birds
that are obviously flighted (most extant bird species) and those that
are obviously flightless (ratites, penguins, dodo, etc) there is a
"gray area" of birds that have lost some of their flight-related
feature, and are exceedingly weak fliers ("semi-flightless").  Many
species of tapucalos that are mostly or entirely terrestrial use
wing-assisted hops and short flutters when travelling along the forest
floor.  For certain tapucalo species it is not known for certain if
they are actually capable of flight at all.  Scrub-birds use their
wings during rapid manoeuvring when on the ground, and in leaping
between vegetation.  Lyrebirds use their wings for extremely short and
clumsy flights and long downhill glides.  And so on.  Poor flight
abilities have been selected for.

Basal avialans like _Archaeopteryx_, _Anchiornis_, _Xiaotingia_, and
_Jinfengopteryx_ may likewise have occupied this "gray zone".  For
small theropods, wing-assisted hops or glides could be useful in dense
habitats when negotiating through or over uneven terrain.  Except,
unlike the "semi-flightless" birds of today, the poor flight abilities
of these basal avialans could be incipient, not derived from better
fliers.




Cheers

Tim