title: A new feather type in a nonavian theropod and the early evolution of feathers.
abstract: All described feathers in nonavian theropods are composite structures formed by multiple filaments. They closely resemble relatively advanced stages predicted by developmental models of the origin of feathers, but not the earliest stage. Here, we report a feather type in two specimens of the basal therizinosaur Beipiaosaurus, in which each individual feather is represented by a single broad filament. This morphotype is congruent with the stage I morphology predicted by developmental models, and all major predicted morphotypes have now been documented in the fossil record. This congruence between the full range of paleontological and developmental data strongly supports the hypothesis that feathers evolved and initially diversified in nonavian theropods before the origin of birds and the evolution of flight.
authors.affiliation: Laboratory of Evolutionary Systematics of Vertebrates, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, 142 Xiwai Street, Beijing 100044, China. xingxu@vip.sina.com
authors.forename: Xing
authors.initials: X
authors.lastname: Xu
authors.forename: Xiaoting
authors.initials: X
authors.lastname: Zheng
authors.forename: Hailu
authors.initials: H
authors.lastname: You
mesh_terms: D000818:Animals; D005075:Biological Evolution; D025061:Dinosaurs / Q000033:anatomy & histology* / Q000145:classification; D005241:Feathers / Q000033:anatomy & histology*