Respiratory faculties of amphibious and terrestrial craniotes

Abstract

This chapter introduces the ‘who has what’ in terms of air-breathing respiratory faculties for craniotes. Air breathing has arisen independently dozens of times among ray-finned fishes, but none has become completely terrestrial. The lobe-finned fishes eventually gave rise to amphibians and amniotes, and we see an increased importance of primarily lung-based air breathing. A muscular mechanism for lung ventilation (a buccal pump in amphibians and primarily a negative pressure aspiration mechanism in amniotes), pulmonary veins that return oxygenated blood to the heart, and some mechanism for partial or complete separation of oxygenated and deoxygenated blood masses at the heart are seen. Each major tetrapod group, in fact, has its own specific breathing mechanism. The chapter examines in some detail low-performance and high-performance faculties, the latter being particularly realized in the diaphragm-powered, ventilated pool system of the mammalian bronchoalveolar lung, and in the cross-current system of the avian lung–air sac system.