Hind wings in basal birds and the evolution of leg feathers

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.