The family was first described by John Edward Gray in 1821,[5] and later assigned to taxonomic ranks within the order Proboscidea. Elephantidae has been revised by various authors to include or exclude other extinct proboscidean genera.
Description
Elephantids are distinguished from more primitive proboscideans like gomphotheres by their teeth, which have parallel lophs, formed from the merger of the cusps found in the teeth of more primitive proboscideans, which are bound by cement.[6] In later elephantids, these lophs became narrow lamellae,[7] with the number of lophs/lamellae per tooth, as well as the tooth crown height (hypsodonty) increasing over time.[8] Elephantids chew using a proal jaw movement involving a forward stroke of the lower jaws, different from the oblique movement using side to side motion of the jaws in more primitive proboscideans.[9] The most primitive elephantid Stegotetrabelodon had a long lower jaw with lower tusks and retained permanent premolars similar to many gomphotheres, while modern elephantids lack permanent premolars, with the lower jaw being shortened (brevirostrine) and lower tusks being absent.[8]
Phylogeny of recent and Late Pleistocene elephantid species, including Palaeoloxodon and mammoths, showing the hybridisation between African forest elephants and Palaeoloxodon, after Palkopoulou et al. 2018"Man, and the elephant" plate from Hawkins's A comparative view of the human and animal frame, 1860Skeleton of Mammuthus meridionalis at the French Museum of Natural History
Some authors have suggested to classify the family into two subfamilies, Stegotetrabelodontinae, which is monotypic, only containing Stegotetrabelodon, and Elephantinae, containing all other elephantids.[8] Recent genetic research has indicated that Elephas and Mammuthus are more closely related to each other than to Loxodonta, with Palaeoloxodon closely related to Loxodonta. Palaeoloxodon also appears to have received extensive hybridisation with the African forest elephant, and to a lesser extent with mammoths.[10]
Evolution of elephants from the ancient Eocene (bottom) to the modern day (top)
Elephantids are thought to have evolved from gomphotheres, with some authors proposing the most likely ancestors to be African species of the "tetralophodont gomphothere" Tetralophodon.[11] The earliest members of the family, are known from the Late Miocene, around 9–10 million years ago.[12] The modern genera of elephants and mammoths had diverged from each other by the end of the Miocene, around 5 million years ago. Elephantids began to migrate out of Africa during the Pliocene, with mammoths and Elephas arriving in Eurasia around 3–3.8 million years ago.[13] Around 1.5 million years ago, mammoths migrated into North America.[14] At the end of the Early Pleistocene, around 0.8 million years ago, Palaeoloxodon migrated out of Africa, becoming widespread across Eurasia, from Western Europe to Japan.[15]Palaeoloxodon and Mammuthus became extinct during the Late Pleistocene-Holocene, with the last population of mammoths persisting on Wrangel Island until around 4,000 years ago.[16]
^H. T. Mackaye, M. Brunet, and P. Tassy. 2005. Selenetherium kolleensis nov. gen. nov. sp.: un nouveau Proboscidea (Mammalia) dans le Pliocène tchadien. Geobios 38(6):765-777
^Kalb, J. E.; & Froehlich, D. J. (1995). "Interrelationships of Late Neogene Elephantoids: New evidence from the Middle Awash Valley, Afar, Ethiopia". Geobios. 28 (6): 727–736. Bibcode:1995Geobi..28..727K. doi:10.1016/s0016-6995(95)80068-9.
^Shoshani, J.; Ferretti, M.P.; Lister, A.M.; Agenbroad, L.D.; Saegusa, H.; Mol, D.; Takahashi, K. (2007). "Relationships within the Elephantinae using hyoid characters". Quaternary International. 169–170: 174–185. Bibcode:2007QuInt.169..174S. doi:10.1016/j.quaint.2007.02.003.
^Maglio, Vincent J. (1973). "Origin and Evolution of the Elephantidae". Transactions of the American Philosophical Society. 63 (3): 16. doi:10.2307/1006229. JSTOR1006229.
^H. Saegusa, H. Nakaya, Y. Kunimatsu, M. Nakatsukasa, H. Tsujikawa, Y. Sawada, M. Saneyoshi, T. Sakai Earliest elephantid remains from the late Miocene locality, Nakali, Kenya Scientific Annals, School of Geology, Aristotle University of Thessaloniki, Greece VIth International Conference on Mammoths and Their Relatives, vol. 102, Grevena -Siatista, special volume (2014), p. 175
Molar of Tetralophodon, a "tetralophodont gomphothere"
Worn molar of Stegotetrabelodon, a primitive elephantid
Molar of a modern African bush elephant (Loxodonta africana)
Tooth of Mammuthus sp..jpg)
