Complexities and novelties in the early evolution of avian flight, as seen in the Mesozoic Yanliao and Jehol Biotas of Northeast China

Recently reported specimens from the Mid-Late Jurassic Yanliao (or Daohugou) Biota and Early Cretaceous Jehol Biota of Northeast China suggest that the early evolution of avian flight involved a surprising amount of homoplasy and evolutionary experimentation. Pennaceous feathers of variable size, structure, and extent occur on the hindlimbs of numerous Jehol and Yanliao paravian theropods, including some basal birds, and clearly had an...