Reinterpretation of purported molting evidence in the Thermopolis Archaeopteryx

Abstract

Feather molt is an important process in the avian annual cycle that is affected by several variables, including flight ability, migration strategy, habitat preference, and morphology 1 , 2 . Understanding molt strategies in feathered non-avian dinosaurs and stem birds has the potential to expand our knowledge of the ecology and flight ability of these extinct species and shed light on the evolution of this important process in birds. Kaye et al. 3 described purported feather sheaths in the Thermopolis Archaeopteryx (WDC-CSG-100 4 ) using laser-stimulated fluorescence to amplify what is visible under normal light and ultraviolet-induced fluorescence 4 . They suggested this finding may support a bidirectional sequential molt with inward and outward renewal of the primary feathers from a single center (node), a pattern that rarely occurs in Neoaves (crown birds). Kaye et al. claim this discovery represents the earliest record of sequential molting in a pennaraptoran (150 million years old), and the first record of molt in an avialan 3 .