Functional constraints on the number and shape of flight feathers

Locomotor ability is dependent on the structures through which movement is produced—in the case of avian flight, the most physically demanding form of vertebrate locomotion, flight ability is reflected in the structure and morphology of the feathered wing surface. Data from modern birds reveal that the number of flight feathers is tightly constrained in flying taxa, and the degree of primary vane asymmetry is also strongly related to flight. Data pertaining to the timing of flight loss in extant lineages reveal different rates of change in these morphology-function relationships. Applying these data to extinct pennaraptorans suggests that anchiornithines and the oviraptorosaur Caudipteryx are secondarily flightless. The phylogenetic position of these species suggests that volant abilities are plesiomorphic to Pennaraptora.