Postcranial skeletal pneumaticity and air-sacs in the earliest pterosaurs.

Patterns of postcranial skeletal pneumatization (PSP) indicate that pterosaurs possessed components of a bird-like respiratory system, including a series of ventilatory air-sacs. However, the presence of PSP in the oldest known pterosaurs has not been unambiguously demonstrated by previous studies. Here we provide the first unequivocal documentation of PSP in Late Triassic and earliest Jurassic pterosaurs. This demonstrates that PSP and, by inference, air-sacs were probably present in the common ancestor of almost all known pterosaurs, and has broader implications for the evolution of respiratory systems in bird-line archosaurs, including dinosaurs.