Cetaceans.

Cetaceans display numerous anatomic and physiologic adaptations to life in a dense, three-dimensional medium. Their bodies have changed radically from those of their terrestrial ancestors, yet their behaviors and types of social organization are broadly similar to those of animals on land. An exploration of cetacean ways helps in understanding how habitat influences habits. For example, it is now recognized that in some important ways, cetacean residents of the open ocean resemble some of their mammalian relatives on the savanna. As air breathers that are inseparably tied to the surface, cetaceans are highly trackable; they may thus help in the monitoring of habitat degradation and other long-term ecologic change.