The African and Indian elephants are the only 2 surviving species of a once diverse and widespread group.
Proboscids evolved from a basal stock of primitive hoofed animals that also gave rise to the modern hyraxes (see pp. 262-265) and the aquatic sirenians (the dugongs and manatees; see pp. 226-229). From their origins in northern India in the Eocene as pig-sized creatures without tusks or trunks, pro-boscids had evolved by Pliocene times, 50 million years later, into giants that had spread over all continents except for Australia and Antarctica.
Their evolution involved a progressive increase in size, the development of long pillarlike legs to support the immense weight, the extension of a proboscis or trunk, the massive enlargement of the head, and a shortening of the neck. Also, there was a reduction of the teeth to a few grinding molars — except for 1 or 2 pairs which were modified into specialized tusks. The trunk and tusks were originally adaptations that enabled a tall, short-necked animal to reach food on the ground or in the trees, but they also function in display.
By Pleistocene times, about 2 million years ago, mammoths and mastodonts flourished over the northern continents, only to suffer mass extinction in the encroaching ice. In Siberia, some have been found frozen in ice, their flesh and fur perfectly preserved. Meanwhile, the Elephantidae, the only family of the order to survive, had already undergone rapid evolution in warmer climates to the south. Four suborders are known.
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