Feathers are complex, branched, keratinized epidermal features commonly associated with class birds or birds (Bock, 2000). Cells in the epidermis called keratinocytes are the structural components of feathers; however, the keratin protein varies in its distribution and can be of different types (Prum, 2002). Many functions involved in feathers include thermal insulation, flight, plumage cleaning, heat protection, sound production, chemical defenses, plumage water repulsion, social communication, body streamlining, and the sensation of touch (Bock, 2000; Prum, 2002). . A wide variety of feathers have been characterized. The feathers that cover the body are known as contour feathers (Bock, 2000). The contour feathers that cover the wings are called flight feathers, while those that cover the tail are called rhetrices (Bock, 2000). Additional types of feathers include half-feathers, down and powdered feathers, bristles and half-bristles, threadplumes, courtship plumes, and sebaceous gland feathers (Bock, 2000). General characteristics of feathers include the presence of a quill, which anchors the feather to the bird's integument (Bock, 2000). Barbs, or closely spaced branches, are attached to the central stem known as the rachis (Bock, 2000). The barbs on each side of the rachis form a fin (Bock, 2000). The proximal and distal barbules originate from barbs; the proximal barbules are near the base of the feather while the distal barbules are at the tip of the feather (Bock, 2000; Prum, 2002). When these barbules interlock, the structure of the vane is preserved (Bock, 2000). Interestingly, feathers are not limited to birds; fossil evidence from Archeopteryx lithographica has shown that feathers originated in pre-avian dinosaurs (Prum, 1999). You understand... half of the document...... RO 1999. Development and evolutionary origin of feathers. J. Esp. Biol. 285: 291-306.Prum, R. O. 2002. The evolutionary origin and diversification of feathers. D. Rev. Biol. 77: 261-291. Schweitzer, M.H., Watt, J.A., Avci, R., Knapp, L., Chiappe, L., Norell, M., et al. 1999. J. Esp. Zool. 285: 146-157.Vinther, J., Briggs, DEG, Clarke, J., Mayr, G., Prum, RO 2010. Structural coloration in a fossil feather. Biol. Lett. 6: 128-131.Xu, X. 2006. Feathered dinosaurs from China and the evolution of major avian characters. Integral Zool. 1:4-11.Xu, X., Zhou, Z., Prum, RO 2001. Branched integument structures in Sinornithosaurus and the origin of feathers. Nature 410: 200-203.Zhang, F., Kearns, S.L., Orr, P.J., Benton, M.J., Zhou, Z., Johnson, D., et al. 2010. Fossilized melanosomes and color of Cretaceous dinosaurs and birds. Nature 463: 1075-1077.