Pterosaur diversity: Untangling the influence of sampling biases, Lagerstätten, and genuine biodiversity signals

Abstract

Pterosaurs were a diverse and successful group of Mesozoic reptiles with an evolutionary history that extended for approximately 145Myr. Recent attempts to understand species-richness trajectories for pterosaurs have led to them becoming a focal group for ongoing debate about the importance of sampling biases in determining observed species-richness patterns in the vertebrate fossil record. Here, we reanalyse pterosaur species-richness through time, and make statistical comparisons to proxies for pterosaur fossil record sampling and ‘global’ terrestrial tetrapod sampling, using several approaches including generalised least-squares multiple regression models. Moreover, we make quantitative comparisons between species-richness and morphological diversity (disparity). Sampling of the pterosaur fossil record shows substantial temporal heterogeneity, with Cretaceous pterosaur records more commonly recovered from terrestrial environments, and with sampling proxies for Cretaceous pterosaurs closely tracking ‘global’ sampling proxies for terrestrial tetrapods. The similarities between pterosaur-based and ‘global’ sampling proxies for Cretaceous data call into question the hypothesis that observed correlations between pterosaur sampling proxies and pterosaur species-richness result from mere ‘redundancy’. Multiple regression modelling supports the hypothesis that much of the variation present in pterosaur palaeobiodiversity curves results from a combination of the presence or absence of Lagerstätten (sites of exceptional preservation) and a ‘background’ sampling signal that may reflect temporal variation in fossiliferous sedimentary rock. Despite these evident strong biases in the pterosaur record, it seems plausible that both species-richness and disparity peaked relatively late in the evolutionary history of pterosaurs (during the Late Jurassic–Early Cretaceous), although an absence of pterosaur-bearing terrestrial Lagerstätten in the Late Triassic–Early Jurassic fossil record means that caution is required. It is possible that a late peak in diversity may reflect the ecological radiation of pterodactyloid pterosaurs from the Late Jurassic onwards, which has been linked to increased terrestrial locomotory abilities and ecological niche occupancy and relaxed constraints upon body size evolution.