Climate-mediated diversification of turtles in the Cretaceous

Abstract

Chelonians are ectothermic, with an extensive fossil record preserved in diverse palaeoenvironmental settings: consequently, they represent excellent models for investigating organismal response to long-term environmental change. We present the first Mesozoic chelonian taxic richness curve, subsampled to remove geological/collection biases, and demonstrate that their palaeolatitudinal distributions were climate mediated. At the Jurassic/Cretaceous transition, marine taxa exhibit minimal diversity change, whereas non-marine diversity increases. A Late Cretaceous peak in ‘global' non-marine subsampled richness coincides with high palaeolatitude occurrences and the Cretaceous thermal maximum (CTM): however, this peak also records increased geographic sampling and is not recovered in continental-scale diversity patterns. Nevertheless, a model-detrended richness series (insensitive to geographic sampling) also recovers a Late Cretaceous peak, suggesting genuine geographic range expansion among non-marine turtles during the CTM. Increased Late Cretaceous diversity derives from intensive North American sampling, but subsampling indicates that Early Cretaceous European/Asian diversity may have exceeded that of Late Cretaceous North America.

Abstract

Turtles are ectothermic vertebrates that have experienced major environmental perturbations. Here the authors show that the geographical distribution of turtles was mediated by climate throughout the Mezozoic and show an increase in diversity of non-marine turtles starting in the Early Cretaceous.