Anchiornis, one of the earliest known feathered dinosaurs ever discovered, was found to have the ability to fly. Using electron microscopy and chemical analyses, researchers found that Anchiornis feathers were predominated by thicker α-keratins rather than thinner β-keratins, and lacked the biomechanical properties needed for flight. The findings suggest that even though Anchiornis feathers were not suitable for powerful flight, their molecular composition may signify an intermediate stage in the evolution of avian flight feathers.

Reference: PAN Yanhong, et al., 2019. The molecular evolution of feathers with direct evidence from fossils. PNAS. DOI: http://doi.org/10.1073/pnas.1815703116.