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Hind Wings in Basal Birds and the Evolution of Leg Feathers

Science  15 Mar 2013:
Vol. 339, Issue 6125, pp. 1309-1312
DOI: 10.1126/science.1228753

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Four-Winged Birds?

Recently, nonavialan dinosaurs with feathers on their fore- and hindlimbs have been described. Zheng et al. (p. 1309) describe eleven basal avialan fossils with clear evidence of feathered hindlimbs. Together these fossils show that early avialans possessed four wings, rather than two. A gradual reduction in hindlimb feathering eventually yielded the two-wing condition in today's birds. Such a transition may have accompanied a locomotory decoupling of the fore- and hindlimbs, which facilitated the development of the forelimbs into flight-capable wings.

Abstract

Recent discoveries of large leg feathers in some theropods have implications for our understanding of the evolution of integumentary features on the avialan leg, and particularly of their relevance for the origin of avialan flight. Here we report 11 basal avialan specimens that will greatly improve our knowledge of leg integumentary features among early birds. In particular, they provide solid evidence for the existence of enlarged leg feathers on a variety of basal birds, suggest that extensively scaled feet might have appeared secondarily at an early stage in ornithuromorph evolution, and demonstrate a distal-to-proximal reduction pattern for leg feathers in avialan evolution.

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