A new darwinopteran pterosaur reveals arborealism and an opposed thumb.

Pterosaurs, which lived during the Mesozoic, were the first known vertebrates to evolve powered flight. Arboreal locomotion has been proposed for some taxa, and even considered to have played a role in the origin of pterosaur flight. Even so, there is still need for comprehensive quantitative ecomorphological analyses. Furthermore, skeletal adaptations correlated to specialized lifestyles are often difficult to recognize and interpret in fossils. Here we report on a new darwinopteran pterosaur that inhabited a unique forest ecosystem from the Jurassic of China. The new species exhibits the oldest record of palmar (or true) opposition of the pollex, which is unprecedented for pterosaurs and represents a sophisticated adaptation related to arboreal locomotion. Principal-coordinate analyses suggest an arboreal lifestyle for the new species but not for other closely related species from the same locality, implying a possible case of ecological niche partitioning. The discovery adds to the known array of pterosaur adaptations and the history of arborealism in vertebrates. It also adds to the impressive early bloom of arboreal communities in the Jurassic of China, shedding light on the history of forest environments.