Scales in the Early Cretaceous bird Gansus from China provide evidence on the evolution of avian scales

Abstract

Most modern birds have scales covering feet, but our knowledge of early avian scales is limited, mainly due to their scarcity in the fossil record. Here we describe the morphological details of scutellate and interstitial scales preserved in IVPP V15077, a specimen of the Early Cretaceous bird Gansus from the Changma Basin in northwestern Gansu Province, Northwest China. These results, combined with previous reports of scutate and reticulate scales, show that all four types of scales present in modern birds already appeared in the Early Cretaceous. The phylogenetic distribution of skin appendages of feet, including feathers and scales, shows that non-avian dinosaurs already evolved scales resembling those in modern birds, and that scales can coexist with feathers on feet, suggesting that avian scales may be homologue with scales of non-avian dinosaurs. However, to further test this hypothesis, more research combined with a strengthened focus on detecting specimens with soft tissue preservation is necessary.