Postcranial skeletal pneumaticity and air-sacs in the earliest pterosaurs

Abstract

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.

Figure 1.

Evidence for postcranial skeletal pneumaticity in early pterosaurs. Raeticodactylus filisurensis, BNM 14524: (a) mid-cervical vertebra, ventral; (b,c) anterior dorsal rib, posterior; (d) third preserved dorsal vertebra, right lateral. Eudimorphodon cf. ranzii, BSP 1994 I 51: (e) mid-cervical vertebra, ventral. Dimorphodon macronyx, NHM R1034: (f) cervical vertebra, ventral. Dimorphodon macronyx, GSM 1546: (g) dorsal vertebrae 5–6, right lateral; (h) dorsal vertebrae 5–12, right lateral. cap, capitulum; con, condyle; cot, cotyle; nsp, neural spine; pnf, pneumatic foramen; poz, postzygapophysis; prz, prezygapophysis; tp, transverse process; tub, tuberculum. Scale bar, 5 mm.