The cetacea

Cetacea

The order Cetacea includes the marine mammals commonly known as whales, dolphins, and porpoises. Cetus is Latin and is used in biological names to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek , meaning "whale" or "any huge fish or sea...

n family Monodontidae comprises two unusual whale

Whale

Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...

 species, the narwhal

Narwhal

The narwhal, Monodon monoceros, is a medium-sized toothed whale that lives year-round in the Arctic. One of two living species of whale in the Monodontidae family, along with the beluga whale, the narwhal males are distinguished by a characteristic long, straight, helical tusk extending from their...

, in which the male has a long tusk, and the white beluga whale. They are native to coastal regions and pack ice around the Arctic Sea, and the far north of the Atlantic and Pacific Oceans.

Both species are medium-sized whales, between three and five metres in length, with a forehead melon

Melon (whale)

The melon is an ovoid-shaped, fatty organ found in the forehead of all toothed whales , including dolphins and porpoises and believed to be used in echolocation....

, and a short or absent snout. They do not have a true dorsal fin, but do have a narrow ridge running along the back, which is much more pronounced in the narwhal. They are highly vocal animals, communicating with a wide range of sounds. Like other whales, they also use echolocation

Animal echolocation

Echolocation, also called biosonar, is the biological sonar used by several kinds of animals.Echolocating animals emit calls out to the environment and listen to the echoes of those calls that return from various objects near them. They use these echoes to locate and identify the objects...

 to navigate.

Monodontids have a wide-ranging carnivorous

Carnivore

A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...

 diet, feeding on fish, molluscs, and small crustaceans. They have reduced teeth, with the beluga having numerous simple teeth, and the narwhal having only two teeth, one of which forms the tusks in males. Gestation

Gestation

Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....

 lasts 14-15 months in both species, and almost always results in a single calf. The young are not weaned

Weaning

Weaning is the process of gradually introducing a mammal infant, either human or animal, to what will be its adult diet and withdrawing the supply of its mother's milk.The process takes place only in mammals, as only mammals produce milk...

 for a full two years, and do not reach sexual maturity until they are five to eight years of age. Family groups travel as part of herds, or 'pods', which may contain several hundred individuals.

Taxonomy

The monodontids, dolphins (Delphinidae) and porpoises (Phocoenidae) together comprise the Delphinoidea

Delphinoidea

Delphinoidea is the largest group of toothed whales with 66 genera in 6 families. The largest living member of the superfamily is the killer whale, which can reach 6 tonnes, while the smallest, Commerson's Dolphin, is also the smallest living cetacean....

 superfamily. Genetic evidence suggests that the porpoises are more closely related to the white whales, and that these two families constitute a separate clade

Clade

A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...

 which diverged from the Delphinoidea within the past 11 mya.

Suborder Odontoceti

• Superfamily Delphinoidea
  Delphinoidea
  Delphinoidea is the largest group of toothed whales with 66 genera in 6 families. The largest living member of the superfamily is the killer whale, which can reach 6 tonnes, while the smallest, Commerson's Dolphin, is also the smallest living cetacean....
  
  
  • Family Monodontidae
    • Subfamily Delphinapterinae
      • Genus Delphinapterus
        • Delphinapterus leucas, Beluga
      • Genus † Denebola
        Denebola brachycephala
        Denebola brachycephala is an extinct whale belonging to the family Monodontidae. It is the first known ancestor of the beluga and dates from the Upper Miocene period. A fossil was found in the Baja California peninsula, indicating that the family once existed in warmer waters....
        
        
        • Denebola brachycephala
          Denebola brachycephala
          Denebola brachycephala is an extinct whale belonging to the family Monodontidae. It is the first known ancestor of the beluga and dates from the Upper Miocene period. A fossil was found in the Baja California peninsula, indicating that the family once existed in warmer waters....
          
          
    • Subfamily Monodontinae
      • Genus Monodon
        • Monodon monoceros, Narwhal
          Narwhal
          The narwhal, Monodon monoceros, is a medium-sized toothed whale that lives year-round in the Arctic. One of two living species of whale in the Monodontidae family, along with the beluga whale, the narwhal males are distinguished by a characteristic long, straight, helical tusk extending from their...