UNC emeritus professor Alan Fedducia has long argued that supposed “proto” precursors to these structures are simply collagen fibers or ossified tendons. They aren’t teeth, but pulp caps are gradually reabsorbed into the rachis during the formation of these structures. The disintegration of the “powder down” variety of these structures produces copious amounts of fine keratin dust. Hooklets and cilia branch from the (*) barbules of these structures. Rectrices and remiges are specialized types of the contour variety of these structures which possess an expansive vane. These structures develop in bloody white sheaths as pins. Raised “knobs'' on the ulna are indicative of these structures in fossils, which likely evolved to provide insulation. For 10 points, preening is the rearrangement of what bristled, water-proof structures whose aerodynamic qualities help birds to fly? ■END■
ANSWER: feathers [accept contour feathers or pennaceous feathers and down feathers; accept flight feathers; accept pin feathers] (Feduccia is a leading proponent in the theory that birds didn’t evolve from dinosaurs, but rather they evolved from a related lineage.)
<KT, Biology>
= Average correct buzz position