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Prum's chapter on feather evolution

I haven't seen this yet, but it looks like the usual top-notch stuff from Richard Prum...

Prum, R.O. (2005) The evolution of feather diversity and function: Exaptation, functional redundancy and historical contingency. In: Briggs, D.E.G. (ed.) Evolving Form and Function: Fossils and Development. p.245-256.

ABSTRACT: "Because of the lack of primitive feather morphologies, for most of the last 150 years, studies of feather evolution had to extrapolate backwards from modern feathers to their unknown morphological antecedents. Most traditional studies adopted functional hypotheses for the evolution of feathers and then hypothesized series of logical functional intermediates. The most popular functional hypothesis was that feathers evolved for flight, but many others were also proposed. During most of the 20th century, research on feather evolution did not focus on development, resulting in many evolutionary theories that were developmentally implausible. The developmental theory of the evolution of feathers hypothesized that feathers evolved through a series of developmental novelties and that stages could be reconstructed from the hierarchical relationships among events in feather development. Since 1998, fossil discoveries from the early Cretaceous Yixian Formation of Liaoning, China, confirm key predictions of the developmental theory, including the hypotheses that that plumulaceous feathers are primitive to pennaceous feathers, and that feathers evolved in a terrestrial context before the evolution of flight. The phylogenetic distribution of fossil feathers in theropods confirms that complex, pennaceous feathers, having evolved for other reasons, were co-opted for use in flight. Thus, feathers are a premier example of exaptation: the evolution of a derived function for a plesiomorphic structure. Feather evolution may have involved periods when a diversity of functionally redundant structures was maintained before the origin of subsequent novelties. Thus, episodes of weak selection on feather variants were likely important in fostering evolutionary exploration of the potential feather morphospace that later gave rise to subsequent novelties."