Hind Wings in Basal Birds and the Evolution of Leg Feathers

Abstract

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.