Vertebrate Zoology - V. M. Konstantinov 2011

Chordates
Terrestrial, or Tetrapod, Vertebrates — Vertebrates with Embryonic Membranes
Class Mammals — Subclass Theria — Suborder Toothed Whales

Species of the suborder Odontoceti (toothed whales) are characterized by the presence of Teeth, the number of which in many species is very large (up to 240). All teeth are uniform in Structure, featuring a simple single-cusped crown. There are no hairs on the HEAD, not even rudimentary ones. The characteristic Asymmetry of the Skull is apparently associated with the specialization of the nasal passages, in which one of them has taken on the function of a sound-producing apparatus used for echolocation. The latter is best developed in deep-diving and fast-swimming species. Ultrasound during echolocation is emitted directionally, facilitated by the concave surface of the anterior part of The Skull and the fatty cushion lying above it, which act as a kind of reflector or acoustic lens.

The suborder includes several families.

River dolphins (Platanistidae) are the most ancient group of modern toothed whales, having emerged in the Miocene. They inhabit the rivers of South America, India, and China, feeding on fish, worms, and Mollusks. A typical species is the Amazon river dolphin, or boto (Inia geoffrensis).

Dolphins (Delphinidae) are small (1–10 m), mostly gregarious animals distributed predominantly in the warm and temperate waters of the World Ocean. Their Nervous system is highly developed; they adapt well to captivity and are easily trained. Their acoustic signaling and echolocation are highly sophisticated. Several species inhabit the Black Sea, such as the short-beaked common dolphin (Delphinus delphis) and the bottlenose dolphin (Tursiops truncatus). Dolphins are also found in the Baltic Sea, the Barents Sea, and the seas of the Far East. Distributed in the seas of the Arctic Ocean and the northern seas of the Pacific Ocean is the beluga whale, or white whale (Delphinapterus leucas), a large species reaching up to 6 m in length (see Fig. 202, 5). All these species feed on fish and undertake extensive Migrations driven by fish movements.

Sperm whales (Physeteridae) comprise only two species.

The sperm whale (Physeter catodon) is the largest toothed whale (see Fig. 202, 3), with a length of 10–21 m. It is distributed primarily in the warm waters of all oceans (excluding the Arctic Ocean). Within Russia, it visits the seas of the Far East during the summer. It feeds on cephalopods (octopuses, squids) and, less frequently, on bottom-dwelling fish, diving to depths of up to 300 m.