Evolution and extinct relatives
Over 180 extinct members and three major evolutionary radiations of the order Proboscidea have been recorded.[17] The earliest proboscids, the African Eritherium and Phosphatherium of the late Paleocene, heralded the first radiation.[18] The Eocene included Numidotherium, Moeritherium, and Barytherium from Africa. These animals were relatively small and aquatic.
Later on, genera such as Phiomia and Palaeomastodon arose; the latter likely inhabited forests and open woodlands. Proboscidean diversity declined during the Oligocene.[19] One notable species of this epoch was Eritreum melakeghebrekristosi of the Horn of Africa, which may have been an ancestor to several later species.[20] The beginning of the Miocene saw the second diversification, with the appearance of the deinotheres and the mammutids. The former were related to Barytherium and lived in Africa and Eurasia,[21] while the latter may have descended from Eritreum[20] and spread to North America.[21]
The second radiation was represented by the emergence of the gomphotheres in the Miocene,[21] which likely evolved from Eritreum[20] and originated in Africa, spreading to every continent except Australia and Antarctica. Members of this group included Gomphotherium and Platybelodon.[21] The third radiation started in the late Miocene and led to the arrival of the elephantids, which descended from, and slowly replaced, the gomphotheres.[22] The African Primelephas gomphotheroides gave rise to Loxodonta, Mammuthus, and Elephas. Loxodonta branched off earliest around the Miocene and Pliocene boundary while Mammuthus and Elephas diverged later during the early Pliocene. Loxodonta remained in Africa while Mammuthus and Elephas spread to Eurasia, and the former reached North America. At the same time, the stegodontids, another proboscidean group descended from gomphotheres, spread throughout Asia, including the Indian subcontinent, China, southeast Asia, and Japan. Mammutids continued to evolve into new species, such as the American mastodon.[23]
