Ventilation and gas exchange during treadmill locomotion in the American alligator (Alligator mississippiensis)

A number of anatomical characters of crocodilians appear to be inconsistent with their lifestyle as sit-and-wait predators. To address this paradoxica l association of characters further, we measured lung ventilation and respi ratory gas exchange during walking in American alligators (Alligator missis sippiensis). During exercise, ventilation consisted of low-frequency, large -volume breaths. The alligators hyperventilated severely during walking wit h respect to their metabolic demands. Air convection requirements were amon g the highest and estimates of lung P-CO2 were among the lowest known in ai r-breathing vertebrates. Air convection requirements dropped immediately wi th cessation of exercise. These observations indicate that the ventilation of alligators is not limited by their locomotor movements. We suggest that the highly specialized ventilatory system of modern crocodilians represents a legacy from cursorial ancestors rather than an adaptation to a lifestyle as amphibious sit-and-wait predators.