The pterosaurs were a diverse 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 containing the largest flying organisms. The sudden appearance and large suite of morphological features of this group were suggested to be the result of it originating in terrestrial environments, where the pterosaur fossil record has traditionally been poor [1, 2], and its many features suggested to be adaptations to those environments [1, 2]. However, little evidence has been available to test this hypothesis, and it has not been supported by previous phylogenies or early pterodactyloid discoveries. We report here 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 confirms this species as the basalmost pterodactyloid and reconstructs 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, indicating that pterosaurs lived in or were at least adapted to the environments in which they were preserved.

A fundamental contribution of paleobiology to macroevolutionary theory has been the illumination of deep time patterns of diversification. However, recent work has suggested that taxonomic diversity counts taken from the fossil record may be strongly biased by uneven spatiotemporal sampling. Although morphological diversity (disparity) is also frequently used to examine evolutionary radiations, no empirical work has yet addressed how disparity might be affected by uneven fossil record sampling.Here, we use pterosaurs (Mesozoic flying reptiles) as an exemplar group to address this problem. We calculate multiple disparity metrics based upon a comprehensive anatomical dataset including a novel phylogenetic correction for missing data, statistically compare these metrics to four geological sampling proxies, and use multiple regression modeling to assess the importance of uneven sampling and exceptional fossil deposits (Lagerstätten). We find that range-based disparity metrics are strongly affected by uneven fossil record sampling, and should therefore be interpreted cautiously. The robustness of variance-based metrics to sample size and geological sampling suggests that they can be more confidently interpreted as reflecting true biological signals.In addition, our results highlight the problem of high levels of missing data for disparity analyses, indicating a pressing need for more theoretical and empirical work. K E Y W O R D S :Disparity, diversity, missing data, Pterosauria, sampling biases.

The largest known flying organisms are the azhdarchid pterosaurs, a pterodactyloid clade previously diagnosed by the characters of their extremely elongate middle-series cervical vertebrae. The named species of the Azhdarchidae are from the Late Cretaceous. However, isolated mid-cervical vertebrae with similar dimensions and characters have been referred to this group that date back to the Late Jurassic, implying an almost 60 million year gap in the fossil record of this group and an unrecorded radiation in the Jurassic of all the major clades of the Pterodactyloidea. A new pterosaur from the Early Cretaceous of Liaoning Province of China, Elanodactylus prolatus gen. et sp. nov., is described with mid-cervical vertebrae that bear these azhdarchid characters but has other postcranial material that are distinct from the members of this group. Phylogenetic analysis of the new species and the Pterodactyloidea places it with the Late Jurassic vertebrae in the Late Jurassic-Early Cretaceous Ctenochasmatidae and reveals that the characters of the elongate azhdarchid vertebrae appeared independently in both groups. These results are realized though the large taxon sampling in the analysis demonstrating that the homoplastic character states present in these two taxa were acquired in a different order in their respective lineages. Some of these homoplastic characters were previously thought to appear once in the history of pterosaurs and may be correlated to the extension of the neck regions in both groups. Because the homoplastic character states in the Azhdarchidae and Ctenochasmatidae are limited to the mid-cervical vertebrae, these states are termed convergent based on a definition of the term in a phylogenetic context. A number of novel results from the analysis presented produce a reorganization in the different species and taxa of the Pterodactyloidea.

The pterosaurs, Mesozoic flying reptiles, attained wingspans of more than 10 m that greatly exceed the largest birds and challenge our understanding of size limits in flying animals. Pterosaurs have been used to illustrate Cope’s rule, the influential generalization that evolutionary lineages trend to increasingly large body sizes. However, unambiguous examples of Cope’s rule operating on extended timescales in large clades remain elusive, and the phylogenetic pattern and possible drivers of pterosaur gigantism are uncertain. Here we show 70 million years of highly constrained early evolution, followed by almost 80 million years of sustained, multi-lineage body size increases in pterosaurs. These results are supported by maximum-likelihood modelling of a comprehensive new pterosaur data set. The transition between these macroevolutionary regimes is coincident with the Early Cretaceous adaptive radiation of birds, supporting controversial hypotheses of bird–pterosaur competition, and suggesting that evolutionary competition can act as a macroevolutionary driver on extended geological timescales.