Abstract

Pterosaurs −the flying reptiles− were the first vertebrates to evolve powered flight1 and one of the main evolutionary radiations in Mesozoic terrestrial ecosystems (c. 252−66 Ma), but their origin has remained one of the most outstanding enigmas in palaeontology since the 19th Century2−4. They have been hypothesised as close relatives of a wide variety of reptilian clades, including dinosaur relatives2−8, and there is still a major morphological gap between those forms and the oldest, unambiguous pterosaurs from the Upper Triassic. Driven by recent discoveries of well-preserved cranial remains, μCT scans of fragile skull bones (jaws, braincases), and reliably associated postcrania, we demonstrate that lagerpetids, a group of cursorial, non-volant dinosaur precursors, are the sister group of pterosaurs, sharing numerous synapomorphies across the entire skeleton. This finding substantially shortens the temporal and morphological gap between the oldest pterosaurs and their closest relatives, simultaneously strengthening the evidence that pterosaurs belong to the avian-line of archosaurs. Neuroanatomical features related to the enhanced sensory capabilities of pterosaurs9 are already present in lagerpetids, indicating that they evolved before flight. Our new evidence illuminates the first steps of the assembly of the unique pterosaur body plan, whose conquest of aerial space represents one of the most astonishing morphofunctional innovations in vertebrate evolution.