Four-Winged Birds?

Science  15 Mar 2013:
Vol. 339, Issue 6125, pp. 1251
DOI: 10.1126/science.339.6125.1251-a
CREDIT: ZHENG ET AL.

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.

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