Abstract

The pterosaurs were a diverse, long-lived group of Mesozoic flying reptiles that underwent a body plan reorganization, adaptive radiation, and replacement of earlier forms midway through their long history, resulting in the origin of the Pterodactyloidea, a highly specialized clade that includes the largest known flying organisms. The sudden appearance and large suite of morphological features of this clade had been suggested to be the result of it originating in terrestrial environments, where the pterosaur fossil record has traditionally been poor, and its many features to be adaptations to those environments. However, little evidence has been available to test this hypothesis, and it has not been supported by previous phylogenies or early pterodactyloid discoveries. Here we report the earliest pterosaur with the diagnostic elongate metacarpus of the Pterodactyloidea, Kryptodrakon progenitor, gen. et sp. nov., from the terrestrial Middle-Upper Jurassic boundary of northwest China. Phylogenetic analysis recovers this species as the basal-most pterodactyloid and reconstructs both a terrestrial origin and a predominantly terrestrial history for the Pterodactyloidea. Phylogenetic comparative methods support this reconstruction by means of a significant correlation between wing shape and environment also found in modern flying vertebrates. The elongate metacarpus is both the diagnostic apomorphy for the Pterodactyloidea and likely the key innovation responsible for the radiation of the clade.