Elephants' earliest ancestors weighed about as much as a house cat
Around 60 million years ago in Africa, the first members of the elephant lineage, such as Eritherium, weighed just 3 to 8 kilograms. Their descendants grew into some of the largest land animals ever, including a mastodon estimated at 16 tonnes and tusks longer than a small car.
Proboscidea, named from the Greek for an elephant's trunk, includes today's three elephant species, the African bush, African forest and Asian elephants, plus more than 180 extinct relatives such as mastodons, mammoths, deinotheres and shovel-tusked amebelodonts. Early forms lacked the trademark trunk and tusks. By the late Eocene some, like Barytherium, reached around 2 tonnes, while Moeritherium may have lived partly in water.
The big break came when Afro-Arabia collided with Eurasia about 18 to 19 million years ago, opening a land route out of Africa. Proboscideans spread across Eurasia and, by around 16 to 15 million years ago, crossed the Bering Land Bridge into North America. The elephant family itself arose in Africa roughly 10 million years ago from gomphotheres, and mammoths and the Asian elephant's genus left Africa between 3.6 and 3.2 million years ago.
Size grew as a way to live on low-quality plants, as it did for sauropod dinosaurs. Legs lengthened, feet shortened and gained cushioned pads, the neck shortened to support a heavy skull, and the trunk lengthened to provide reach. Front teeth turned into ever-growing tusks made mostly of dentine; the longest ever recorded, from the mastodon Mammut borsoni found in Greece, measured 5.02 metres. One partial thighbone of an Indian elephant, Palaeoloxodon namadicus, has prompted speculative weight estimates of up to 22 tonnes.
About 23 species remained at the start of the Late Pleistocene. Then the wave of megafauna extinctions swept away mastodons, American gomphotheres and others. Mammoths held on in small island populations near the Bering Strait, surviving on Wrangel Island until about 4,000 years ago. The largest living member, the African bush elephant, has been recorded at 4 metres tall and 10.4 tonnes.
Source: Proboscidea
