Toothed whales

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Toothed whales
Fossil range: Latest Eocene - Recent
Bottlenose Dolphin
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Suborder: Odontoceti
Flower, 1869
Diversity
Around 73; see List of cetaceans or below.
Families

See text.
Cetaceans portal

The toothed whales (systematic name Odontoceti) form a suborder of the cetaceans, including sperm whales, beaked whales, orca1, dolphins, and others. As the name suggests, the suborder is characterized by having teeth, rather than baleen as do animals in the other suborder of cetaceans, Mysticeti. However, fossils indicate that early Baleen whales had teeth as well before evolving baleen, so defining the Odontoceti on teeth alone is problematic, and paleontologists have instead identified other features uniting fossil and modern odontocetes that are not shared by mysticetes. Toothed whales are active hunters, feeding on fish, squid, and in some cases marine mammals.

Contents

Anatomy

Toothed whales have a single blowhole on the top of the head (while the baleen whales possess two of them). The nostrils are not fused; one of them has become dominant over the other.

Toothed whales, as all whales, develop as an embryo in the womb, they are then born as calves, grow into juveniles and finally become adults.

As an adaptation for their echolocation, toothed whale skulls have become asymmetric. Their brains are relatively big, although real growth didn't occur before their echolocation started to evolve. Toothed whales' brains have a poor connection between the two hemispheres and an organ called a melon on their heads is used as a lens to focus sound waves. Vocal cords are not present; their sounds are produced in the blowhole system instead. Toothed whales have lost their sense of smell, as well as their saliva glands.

Except for the Sperm Whale, most toothed whales are smaller than the baleen whales. The teeth differ considerably between the species. They may be numerous, with some dolphins bearing over 100 teeth in their jaws. At the other extreme are the Narwhal with its single long tusk and the almost toothless beaked whales with bizarre teeth only in males. Not all species are believed to use their teeth for feeding. For instance, the Sperm Whale likely uses its teeth for aggression and showmanship.

Behaviour

Vocalizations

Vocalizations are of great importance to toothed whales. While many species also maintain a broad variety of calls to communicate, all species investigated so far use short click sounds for purposes of echolocation. Sperm whales use low frequencies (a few to perhaps 50 kHz), while other employ more narrow band high frequency sounds (porpoises, Cephalorhynchus species like Hector's dolphin). Most dolphin species use very broad band clicks.

Movement

Most toothed whales swim rapidly. The smaller species occasionally ride waves, such as the bow waves of ships. Dolphins can be frequently encountered this way. They are also famous for their acrobatic breaching from the water, e.g. the Spinner Dolphin.

Human impact

The Sperm Whale has been hunted commercially for a long time (see whaling). While small whales like the Pilot Whale today are still being pursued, the main threat for most species is accidental capture in fishing nets.

Keeping small whales (mostly Bottlenose Dolphins, Orcas, or Belugas) in captivity is a great attraction for ocean parks and zoos. However, it is controversial because of the marine mammals' need for large spaces.

Taxonomy

References

  1. ^ "Integrated Taxonomic Information System".


Wikipedia content modification information:

  • This page was last modified on 19 December 2008, at 06:35.

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