Skeletal pneumaticity is the presence of air spaces within bones. Skeletal pneumaticity exists only in synapsids and archosaurs. It is generally produced during development by excavation of bone by pneumatic diverticula (air sacs) from an air-filled space such as the lungs or nasal cavity. Pneumatization is highly variable between individuals, and bones not normally pneumatized can become pneumatized in pathological development.
Pneumatization occurs in the skulls of mammals, crocodilians and birds among extant groups, as well as extinct archosaurs including the dinosaurs and pterosaurs. Pneumatic spaces include the paranasal sinuses and some of the mastoid cells.
Postcranial pneumaticity is usually found only among certain archosaurs—dinosaurs, pterosaurs, and birds. Vertebral pneumatization is widespread among saurischian dinosaurs, and some theropods have quite widespread pneumatization -- Aerosteon riocoloradensis has pneumatization of the ilium, furcula, and gastralia as well.
However, there are unusual instances of postcranial pneumaticity outside Archosauria; the hyoid in the howler monkey Alouatta is pneumatized, and the osteoglossiform fish Pantodon pneumatizes some vertebrae from its swim bladder. In addition, pathological pneumatization has been known to occur in the human atlas vertebra.
- Wedel, M.J. 2005. Postcranial skeletal pneumaticity in sauropods and its implications for mass estimates; pp. 201–228 in Wilson, J.A., and Curry-Rogers, K. (eds.), The Sauropods: Evolution and Paleobiology. University of California Press, Berkeley. (link)
- Sereno, P.C., Martinez, R.N., Wilson, J.A., Varricchio, D.J., Alcober, O.A., Larsson, H.C.E. 2008. Evidence for avian intrathoracic air sacs in a new predatory dinosaur from Argentina. PLoS ONE 3(9): e3303. doi:10.1371/journal.pone.0003303 link
- Bruno Moreira and Peter M. Som. Unexplained Extensive Skull Base and Atlas Pneumatization: Computed Tomographic Findings. Arch Otolaryngol Head Neck Surg, Jul 2010; 136: 731 - 733.