Mammoth
Evolution

The earliest known proboscideans, the clade that contains the elephants, arose about 55 million years ago on the landmass of Afro-Arabia. The closest relatives of the Proboscidea are the sirenians and the hyraxes. The family Elephantidae arose by million years ago in Africa, and includes the living elephants and the mammoths. Among many now extinct clades, the mastodon is only a distant relative of the mammoths, and part of the separate Mammutidae family, which diverged 25 million years before the mammoths evolved.

Following the publication of the woolly mammoths mitochondrial genome sequence in 1997, it has since become widely accepted that mammoths and Asian elephants share a closer relationship to each other than either do to African elephants.

The following cladogram shows the placement of the genus Mammuthus among other proboscideans, based on hyoid characteristics and genetics:

It is possible to reconstruct the evolutionary history of the genus through morphological studies. Mammoth species can be identified from the number of enamel ridges/lamellae on their molars; the primitive species had few ridges, and the amount increased gradually as new species evolved and replaced the former ones. At the same time, the crowns of the teeth became longer, and the skulls became higher from top to bottom and shorter from the back to the front over time to accommodate this.

The earliest mammoths, assigned to the species Mammuthus subplanifrons, are known from southern and eastern Africa, with the earliest records dating to the Late Miocene, around 6.2–5.3 million years ago. By the Late Pliocene, mammoths had become confined to the northern portions of the African continent with remains from this time assigned to Mammuthus africanavus. During the Late Pliocene, by 3.2 million years ago, mammoths dispersed into Eurasia via the Sinai Peninsula. The earliest mammoths in Eurasia are assigned to the species Mammuthus rumanus. The youngest remains of mammoths in Africa are from Aïn Boucherit, Algeria dating to the Early Pleistocene, around 2.3–2 million years ago (with a possible later record from Aïn Hanech, Algeria, dating to 1.95–1.78 million years ago).

Mammuthus rumanus is thought to be the ancestor of Mammuthus meridionalis, which first appeared at the beginning of the Pleistocene, around 2.6 million years ago. Mammuthus meridionalis subsequently gave rise to Mammuthus trogontherii (the steppe mammoth) in Eastern Asia around 1.7 million years ago. Around 1.5–1.3 million years ago, M. trogontherii crossed the Bering Land Bridge into North America, becoming ancestral to Mammuthus columbi (the Columbian mammoth). At the end of the Early Pleistocene Mammuthus trogontherii migrated into Europe, replacing M. meridionalis around 1–0.8 million years ago. Mammuthus primigenius (the woolly mammoth) had evolved from M. trogontherii in Siberia by around 600,000–500,000 years ago, replacing M. trogontherii in Europe by around 200,000 years ago, and migrated into North America during the Late Pleistocene.

A number of dwarf mammoth species, with small body sizes, evolved on islands as a result of insular dwarfism. These include Mammuthus lamarmorai on Sardinia (late Middle-Late Pleistocene), Mammuthus exilis on the Channel Islands of California (Late Pleistocene), and Mammuthus creticus on Crete (Early Pleistocene).
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