Proboscidea (redirected from pachyderma)

Proboscidea [‚prō·bə′sid·ē·ə]

(vertebrate zoology)

An order of herbivorous placental mammals characterized by having a proboscis, incisors enlarged to become tusks, and pillarlike legs with five toes bound together on a broad pad.

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Proboscidea 

an order of mammals. The earliest representatives of the order Proboscidea were relatively small animals; later ones were larger, reaching a height of 4.5 m. The legs are long and columnar. The forelegs are five-toed, and the hind legs are four- or five-toed. The neck is short, and the head almost immovable. The highly developed upper lip and the nose concresce to form the movable proboscis, or trunk. In the earliest representatives the proboscis was very small or apparently absent. The dental system is characterized by the absence of canines (except in Moeritherium) and first incisors. The highly developed second incisors (tusks) are marked by constant growth. The molars have broad chewing surfaces that are nodular or have transverse ridges, sometimes with plates. The teeth are formed from dentine and enamel; only in elephants and some mastodonts is cement deposited between the ridges or plates.

The oldest Proboscidea are known from Africa, where their remains have been found in Middle Eocene deposits. Proboscidea were subsequently widely distributed in Africa, Eurasia, and America. At present they are found only in Africa and South Asia. Most species inhabited tropical rain forests; some were apparently semi-aquatic. Only elephants were adapted to life in diverse environments—forests, forest steppes, steppes, and tundra. There are three suborders: Moeritherioidea, Elephantoidea, and Deinotherioidea. The first and third suborders are extinct.

Elephantoidea include three families: Gomphotheriidae, Mastodontidae, and Elephantidae. Extant species belong only to the last family.

REFERENCES

Osnovy paleontologii: Mlekopitaiushchie. Moscow, 1962.
Osborn, H. F. Proboscidea: A Monograph of the Discovery, Evolution, Migration and Extinction of the Mastodonts and Elephants of the World, vols. 1–2. New York, 1936–42.

V. E. GARUTT