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Toothed Whales

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Orca - Orcinus orca

Orca - Orcinus orca

Photo © Grafissimo / iStockphoto.
Toothed whales (Odontoceti) are small to medium sized cetaceans. Toothed whales, as their name implies, have teeth, a characteristic that distinguishes them from their cousins the baleen whales, which have baleen instead of teeth. The shape, arrangement and number of teeth vary among the different species of toothed whales. There are 71 species of toothed whales, making them a more diverse group of cetaceans than the baleen whales. Toothed whales include oceanic dolphins, riber dolphins, porpoises, belugas, narwhals, beaked whales and the sperm whale.

Toothed whales have only one blowhole located on the top of their (baleen whales have two). In most toothed whale species, the blowhole is on the top of the head (sperm whales are an exception, with the blowhole located at the front left-hand side of the head).

Another feature unique to toothed whales is the melon—a fluid-filled structure in their forehead. The melon occupies most of the area between the animal's blowhole and its beak (snout). The melon is part of the nasal anatomy of toothed whales and is believed to function in echolocation. Toothed whales use ecolocation to navigate as well as to locate prey. Their echolocation sense is quite refined, enabling them to determine the size, shape, distance, speed and surface character of nearby objects.

The teeth of toothed whales are not specialized, that is, toothed whales do not have incisors, canines, premolars and molars. Instead, all of their teeth are uniform in shape (pointed and conical with a single root and either stright or slightly curved in profile). Whales have a single set of teeth that are not replaced throughout their life, the teeth they are born with remain with them (ideally) their entire life. The number of teeth varies by species, with some having more than 40 pairs of teeth (dolphins) and others as few as a single pair of teeth (beaked whales).

Toothed whales feed in an very different manner to baleen whales. Whereas baleen whales filter tiny prey (such as copepods and krill) en masse from the water, toothed whales capture and feed on large individual prey. The diet of toothed whales varies among the different groups. Killer whales form packs and hunt other whales or feed on seals. Sperm whales feed primarily on squid but also supplement their diet occasionally with octopuses. Beaked whales eat both fish and squid. Toothed whales have conical shaped teeth that are especially suited for grasping onto slipppery prey. The toothed whales that feed on fish generally have more teeth than those that feed on invertebrates such as squid or octopuses.

Many toothed whales form social groups called pods. Pods may vary in size from a few individuals to more than 1000 (in the case of some dolphin species). The social structure of many toothed whale species remains unclear but scientists believe that complex interactions and communication are prevalent. Orcas (also known as killer whales), for example, form hunting groups and cooperate in complex ways to herd and take down large prey.

Toothed whales have a wide distribution, with the various species inhabiting oceans throughout the world including deep water habitats as well as coastal waters. Some toothed whales—the river dolphins, for example—live in freshwater.

Classification:

Toothed whales belong to a group of mammals known as the cetaceans. There are 71 species of toothed whales divided into about 6 subgroups: oceanic dolphins, river dolphins, porpoises, beluga and narwhal, beaked whales and sperm whales.

Evolution:

The closest relatives to the toothed whales are the baleen whales. Like all cetaceans, the ancestors of toothed whales were land mammals.
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