Toothed Whales, Overview

This chapter provides the overview of toothed whales. Toothed whales comprise the suborder Odontoceti of the order Cetacea. This suborder includes 10 diverse families, 2 of which contain large numbers of species. There are at least 71 species in all, including the true dolphins, monodontids, river dolphins, porpoises, beaked whales, and sperm whales. These species occur in three primary clades, the superfamilies Delphinoidea (true dolphins, monodontids, and porpoises), Ziphoidea (beaked whales), and Physeteroidea (sperm whales), whereas the affinities of the river dolphins remain uncertain. With the exception of the sperm whale (males of which reach up to 18 m) and the larger beaked whale species (. Berardius and Hyperoodon spp.), most odontocetes are small to medium-sized cetaceans, ranging in size from the Hector's dolphin (1.5 m) to the killer whale (8.5 m). These species show a range of distributions, with some such as river dolphins found only in quite specific areas, whereas others such as sperm whales or killer whales show a global distribution. Toothed whales have developed specialized sound production and reception mechanisms for the use of biosonar. All modern odontocetes are thought to use echolocation, in the same manner as bats, to gain an "image" of their environment. Although only a few species of odontocete are unequivocally known to echolocate, all odontocetes known to produce pulse-like sounds in the wild are assumed to be able to echolocate. Toothed whales are particularly well known for their brain size and rich social lives. The absolute brain size of odontocetes ranges from 840 g in common dolphins to 7820 g in sperm whales. However, a more useful way to compare brain sizes is to use the ratio of brain size to body size, the encephalization quotient (EQ). © 2009