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Archaeopteryx. Credit: Wikipedia
But an analysis described in last week's Nature suggests that this species was actually transitional toward losing flight.
The argument, presented at a paleontology conference, goes as follows: it is known that Archaeopteryx lived on an archipelago within a tropical sea. And there are many examples of birds in isolated locales losing their flight, probably because flight requires so much energy. The most famous example of this probably the ill-fated Dodo in Mauritania; but other examples are the grebe and the rail. Flightless birds have several differences in their skeleton compared to their flying cousins; specifically their wing bones are lighter, and the breastbone lacks a "keel" to anchor the heavy flight muscles. Finally they have more, and more symmetrical feathers. The argument, then, is that the bones and feather imprints of Archaeopteryx fossils fall plausibly within the range of an island flightless bird.
I think that the progressive discovery of feathers on all sorts of dinosaurs does make it seem that there was not a single pathway leading to flight. So the new theory is worth careful consideration. In the absence of a living example, the discussion of this critter's capabilities will have to remain open.