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Structure and function of hindlimb feathers in Archaeopteryx lithographica

¹ Nick Longrich. Department of Biological Sciences, 2500 University Drive NW, University of Calgary, Calgary, Alberta T2N 1N4, Canada. longrich{at}ucalgary.ca

This study examines the morphology and function of hindlimb plumage in Archaeopteryx lithographica. Feathers cover the legs of the Berlin specimen, extending from the cranial surface of the tibia and the caudal margins of both tibia and femur. These feathers exhibit features of flight feathers rather than contour feathers, including vane asymmetry, curved shafts, and a self-stabilizing overlap pattern. Many of these features facilitate lift generation in the wings and tail of birds, suggesting that the hindlimbs acted as airfoils. A new reconstruction of Archaeopteryx is presented, in which the hindlimbs form approximately 12% of total airfoil area. Depending upon their orientation, the hindlimbs could have reduced stall speed by up to 6% and turning radius by up to 12%. Presence of the "four-winged" planform in both Archaeopteryx and basal Dromaeosauridae indicates that their common ancestor used fore- and hindlimbs to generate lift. This finding suggests that arboreal parachuting and gliding preceded the evolution of avian flight.