The classic citation on the nature and evolution of beta keratin is
Brush, AH (1993) The origin of feathers: A novel approach In Avian Biology Vol IX: 212-162. Farner, King & Parks,eds.
The most recent published paper on feather evolution is
Brush, AH (1996) On the Origins of feathers. J. Evol. Biol. 9:131-142.
There are several more papers in press, mostly in the recent Dinofest, SICB and Yale Symposia. However, the most likely to be available soon is
Prumm, R (in press, 1999).The Development and Evolutionary Origin of Feather. J. Exptl. Zool 285(4)
But it is the first two that give the most information on the beta keratins and their incorporation and function in feathers, scales, claws and beaks.
Alan H. Brush
92 High St.
Mystic, CT 06355