In the last few years a large number of depth recordings have added a substantial amount of information about diving depths in aquatic tetrapods. Many dive to at least 200 m on occasion, and some to > 1000 m. The high pressures at such depths may necessitate special adaptations for responding to compression and gas exchange. Effective compensation has been experimentally explained in only a few cases for seals. For example, the seal's respiratory system, because of the unusual compliance of the chest, easily yields to high ambient pressures. This causes compression collapse of the lung and low gas exchange. The result is low blood N2 tensions no matter what the dive depth. Somewhat similar adaptations exist for sea snakes, but the adaptations of sea turtles and birds remain unknown.