title: Origin of archosaurian integumentary appendages: the bristles of the wild turkey beard express feather-type beta keratins.
abstract: The discovery that structurally unique "filamentous integumentary appendages" are associated with several different non-avian dinosaurs continues to stimulate the development of models to explain the evolutionary origin of feathers. Taking the phylogenetic relationships of the non-avian dinosaurs into consideration, some models propose that the "filamentous integumentary appendages" represent intermediate stages in the sequential evolution of feathers. Here we present observations on a unique integumentary structure, the bristle of the wild turkey beard, and suggest that this non-feather appendage provides another explanation for some of the "filamentous integumentary appendages." Unlike feathers, beard bristles grow continuously from finger-like outgrows of the integument lacking follicles. We find that these beard bristles, which show simple branching, are hollow, distally, and express the feather-type beta keratins. The significance of these observations to explanations for the evolution of archosaurian integumentary appendages is discussed.
authors.affiliation: Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA. sawyer@mail.psc.sc.edu
authors.forename: Roger H
authors.initials: RH
authors.lastname: Sawyer
authors.forename: Lynette D
authors.initials: LD
authors.lastname: Washington
authors.forename: Brian A
authors.initials: BA
authors.lastname: Salvatore
authors.forename: Travis C
authors.initials: TC
authors.lastname: Glenn
authors.forename: Loren W
authors.initials: LW
authors.lastname: Knapp
mesh_terms: D000818:Animals; D015153:Blotting, Western; D025061:Dinosaurs / Q000033:anatomy & histology*; D005241:Feathers; D007633:Keratins / Q000235:genetics*; D008855:Microscopy, Electron, Scanning; D012867:Skin / Q000648:ultrastructure*; D014422:Turkeys / Q000033:anatomy & histology* / Q000235:genetics*
chemical_list: D007633:Keratins