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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An order of placental mammals derived from conservative (that is, primitive or ancient) hooved mammal stock (sometimes informally referred to as condylarths), the oldest members known from Paleocene sediments of North Africa. At one point, proboscideans had a wide distribution, having reached every continent except Australia and Antarctica. They included an astonishing variety of forms. However, currently this order consists of only two forms, belonging to the family Elephantidae: the African elephant (Loxodonta africana) and the Asian elephant (Elephas maximus). Features commonly associated with the proboscideans include large body size, enlarged incisors that form paired tusks (relatively small lower tusks were present in the jaws in the majority of extinct forms in addition), and a proboscis (often referred to informally as a trunk). It is important to realize that the very early forms lacked both significant tusks and a proboscis, though they are still formally considered proboscideans. Unlike most modern hooved mammals which have reduced the toe number to four or more often fewer, proboscideans have retained five toes. Throughout their known history, proboscideans have been strictly herbivorous.

Early elephant evolution mostly occurred in Africa during the Eocene and Oligocene. Near the beginning of the Miocene, proboscideans exited Africa and spread all over Europe and Asia, and by the middle Miocene they reached North America. The proboscideans were highly successful in North America, and between 2 and 1.5 million years ago they entered South America across the Panamanian landbridge. Between 12,000 and 10,000 years ago, most of the world's proboscideans became extinct, with only the African and Asian elephants surviving.

There has been considerable debate by paleontologists as to which animals are actually proboscideans, in part because some members of the order bear little or no superficial resemblance to modern forms. Two suborders in the classification below, Deinotherioidea and Barytherioidea, represent such sometimes disputed groups.

Order Proboscidea

     Suborder: Deinotherioidea

                                        Barytherioidea

                                        Moeritheriodea

                                        Elephantoidea

          Infraorder Mammutoidea

               Family Mammutidae

          Infraorder Gomphotherioidea

               Family: Gomphotheriidae

                                        Elephantidae

The conservative proboscideans consist of the members of the suborders Deinotherioidea, Barytherioidea, and Moeritherioidea. Though these animals are considered to be proboscideans, they mostly bear little or no resemblance to elephants. In fact, such typically elephantine characters as tusks and a proboscis do not strictly define the order Proboscidea. Instead, proboscideans are characterized by relatively obscure features in the teeth, shoulder, and ankle. The relationship of these suborders to the advanced suborder Elephantoidea (which includes the living elephants) is not well understood. See also Elephant; Mammalia.

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IN BRIEF: n. - An order of animals including elephants and mammoths; In some classifications included in the genus Martynia and hence the two taxonomic names for some of the unicorn plants.

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