Prum's chapter on feather evolution

[Tim Williams <twilliams_alpha@hotmail.com>]

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."