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
For detailed information on the anatomy of living elephants, see Elephant#Anatomy
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 cementum.[6] In later elephantids, these lophs became narrow lamellae/plates,[7] which are pockets of enamel filled with dentine, which are arranged successively like a concertina.[8] The number of lophs/lamellae per tooth, as well as the tooth crown height (hypsodonty) is greater in later species.[9] 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.[10] 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.[9]
Elephantids are typically sexually dimorphic, with substantially larger males, with an accelerated growth rate over a longer period of time than females. Elephantidae contains some of the largest known proboscideans, with fully-grown males of some species of mammoths and Palaeoloxodon having average body masses of 11 tonnes (24,000lb) and 13 tonnes (29,000lb) respectively, making them among the largest terrestrial mammals ever. One species of Palaeoloxodon, Palaeoloxodon namadicus, has been suggested to have been possibly the largest land mammal of all time, though this remains speculative due to the fragmentary nature of known remains.[11] In comparison to more primitive elephantimorphs like gomphotheres, the bodies of elephantids tend to be proportionally shorter from front to back, as well having more elongate limbs with more slender limb bones.[12]
Living female and juvenile elephants live in matriarchal (female-led) herds of related individuals, with males leaving these groups to live solitarily upon reaching adolescence around 14–15 years of age.[13] Evidence has been found that extinct elephantids, including the most primitive elephantid, Stegotetrabelodon, also lived in herds based on footprint tracks.[13][14]
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.[9] 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.[15]
Evolution of elephantids from the ancient Eocene (bottom) to the modern day (top)
Around 10 million years ago, the earliest members of the family Elephantidae emerged in Africa, having originated from gomphotheres.[16] The earliest members of the modern genera of Elephantidae appeared during the latest Miocene–early Pliocene around 5 million years ago. The elephantid genera Elephas (which includes the living Asian elephant) and Mammuthus (mammoths) migrated out of Africa during the late Pliocene, around 3.6 to 3.2 million years ago.[17] Mammoths then migrated into North America around 1.5 million years ago.[18] At the end of the Early Pleistocene, around 800,000 years ago the elephantid genus Palaeoloxodon dispersed outside of Africa, becoming widely distributed in Eurasia.[19]Palaeoloxodon became extinct as part of the Late Pleistocene extinctions, with mammoths only surviving in relict populations on islands around the Bering Strait into the Holocene, with their latest survival being on Wrangel Island, where they persisted until around 4,000 years ago.[20][21]
↑ 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.
↑ 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.
↑ Maglio, Vincent J. (1973). "Origin and Evolution of the Elephantidae". Transactions of the American Philosophical Society. 63 (3): 16. doi:10.2307/1006229. JSTOR1006229.
↑ Saegusa, H.; Nakaya, H.; Kunimatsu, Y.; Nakatsukasa, M.; Tsujikawa, H.; Sawada, Y.; Saneyoshi, M. & Sakai, T. (2014). "Earliest elephantid remains from the late Miocene locality, Nakali, Kenya"(PDF). In Kostopoulos, D. S.; Vlachos, E. & Tsoukala, E. (eds.). VIth International Conference on Mammoths and Their Relatives. Vol.102. Thessaloniki: School of Geology, Aristotle University of Thessaloniki. p.175. ISBN978-960-9502-14-6.
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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.
Cross section through elephantid molars
