Michael Alan Taylor

Book

Mechanics and Physiology of Animal Swimming

Cambridge University Press

Maddock, L., Bone, Q. & Rayner, J.M.V.

An air-breathing tetrapod's buoyancy depends in part on the animal's contained gas, and therefore on the ambient pressure and depth. An animal can vary gas content as a hydrostatic control mechanism to reach neutral buoyancy at a particular depth. Alternatively, or additionally, it can compensate for buoyancy hydrodynamically, for example by producing lift forces during swimming: this is most effective for animals which contain less gas, and thus swim faster and deeper. Two extreme evolutionary adaptations can be predicted from this, and have indeed appeared through convergent evolution: body density and submerged lung-volume reduction for fast, cruising swimmers and deep divers (cetaceans, phocid pinnipeds and ichthyosaurs) and body density and submerged lung-volume increase for bottom-walkers (sirenians and placodonts). A third strategy, swallowing stones, maximizes the flexibility of hydrostatic control and enables the identification of a third case of convergent evolution in the manoeuvrable underwater flyers (otariid pinnipeds, penguins, and plesiosaurs)

English