| Nakalipithecus | |
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| Top and side views of theNakalipithecusholotype, a jawbone and themolars | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Primates |
| Suborder: | Haplorhini |
| Superfamily: | Hominoidea |
| Family: | Hominidae |
| Genus: | †Nakalipithecus Kunimatsu et al., 2007 |
| Species: | †N. nakayamai |
| Binomial name | |
| †Nakalipithecus nakayamai Kunimatsu et al., 2007 | |
Nakalipithecus nakayamai, sometimes referred to as theNakali ape,[1] is an extinct species ofgreat ape fromNakali, Kenya from about 9.9–9.8 million years ago during theLate Miocene. It is known from a right jawbone with 3molars and from 11 isolated teeth. The jawbone specimen is presumed female as the teeth are similar in size to those of femalegorillas andorangutans. Compared to other great apes, the canines are short, theenamel is thin, and the molars are flatter.Nakalipithecus seems to have inhabited asclerophyllous woodland environment.
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| Two hypotheses onNakalipithecus taxonomy[2] |
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Nakalipithecus was first described from a right jawbone, theholotype KNM-NA46400, and eleven isolated teeth excavated in 2005 by a team of Japanese and Kenyan researchers inmud flow deposits in the Nakali area of northern Kenya's formerRift Valley Province, hence the genus nameNakalipithecus ("Nakali ape"). The species name is in honour of the late Japanese geologist Katsuhiro Nakayama who worked on the expedition. The specimen dates to about 9.9–9.8 million years ago in theLate Miocene. The specimens are housed by theNational Museums of Kenya. The holotype preserves all 3 lowermolars, and the isolated teeth are: a left firstincisor, a right first incisor, a rightcanine, a right third upperpremolar, a left third upper premolar, a right left fourth upper premolar, a left fourth upper premolar, a right first upper molar, a right third upper molar, a left third upper molar, and a left fourth lower premolar.[3]
It is debated if greatapes evolved in Africa or Eurasia given the abundance of early fossil apes species in the latter and the paucity in the former, despite all modern great apes except theorangutan being known from Africa. The first Miocene African ape,Samburupithecus, was discovered in 1982.[4] It is unclear howNakalipithecus is related to other apes. It is possible these Late Miocene African apes werestem great apes closely related to thelast common ancestor of all modern African apes, which existed about 9–8 million years ago.[3]
Nakalipithecus and the 9 million year old GreekOuranopithecus macedoniensis exhibit many similarities with each other, butNakalipithecus has morebasal (primitive) traits, which could indicate that it was the ancestor or closely related to the ancestor ofOuranopithecus.Ouranopithecus, in turn, is postulated to be closely related toaustralopithecines and the human line. This would show that apes evolved in Africa. However, evidence of common ancestry can also be interpreted asconvergent evolution, with similar dental adaptations caused by inhabiting a similar environment, thoughOuranopithecus seems to have consumed more hard objects thanNakalipithecus.[3] A 2017 study ondeciduous fourth premolars—deciduous teeth are less affected by environmental factors as they soon fall out and are replaced by permanent teeth—found thatNakalipithecus and later African apes (including australopithecines) shared more similarities with each other than to Eurasian apes, though drew no clear conclusion on theNakalipithecus–Ouranopithecus relationship.[5]
Nakalipithecus has also been proposed to have been the ancestor to the 8 million year oldChororapithecus, which possibly represents an early member of thegorilla line; if both of these are correct, thenNakalipithecus could potentially represent an early gorilla.[2]
Nakalipithecus has an overall large size, with teeth similar in size to those of female gorillas and orangutans. The specimen is thus presumed female. TheSamburupithecus specimen was also about the same size. Unlike other apes, the canines are short, and as long as they are wide—about 10.7 mm × 10.5 mm (0.42 in × 0.41 in) in height and width respectively. For comparison, the left first incisor is 10.8 mm × 8.6 mm (0.43 in × 0.34 in). The premolars are elongated, and theprotoconid (the cusp on the tongue side) of the third premolar is oriented more cheekwards, which is a distinguishing characteristic of Miocene African apes from Miocene Eurasian apes. Compared to African apes contemporary withNakalipithecus, thetooth enamel on themolars is thinner, and thecusps (which project outward from the tooth) are less inflated, creating a wider basin. In the holotype, the first, second, and third molars are 15.6 mm × 14 mm (0.61 in × 0.55 in), 16.2 mm × 15.8 mm (0.64 in × 0.62 in), and 19.5 mm × 15.1 mm (0.77 in × 0.59 in), respectively. Like modern and some contemporary apes, but unlike earlier East African apes, the first molar is relatively large, with a first molar to second molar ratio of 85%. LikeOuranopithecus and earlySivapithecus (Sivapithecus is known from theIndian subcontinent), but unlike most contemporary and future apes, the third molar was much larger than the second, with a third molar to second molar ratio of 115%, though this ratio is smaller than that of the later Southeast AsianKhoratpithecus. The mandible is less robust (heavily built) than those of contemporary Eurasian Miocene apes, except forOuranopithecus.[3]
During the Late Miocene, East Africa, theSahara, the Middle East, and Southern Europe all appear to have been predominantly seasonalsclerophyllousevergreen woodland environments. Nakali appears to have been dominated byC3 (forest) plants.Nakalipithecus is known from the Upper Beds, which comprise lakeside or riverine deposits.[3] Climate change caused the expansion of grasslands in Africa from 10–7 million years ago, likely fragmenting populations of forest-dwelling primates, leading to extinction.[6]
Nakali has also yielded ablack rhino specimen,[7] the pigNyanzachoerus, anantelope, the hippoKenyapotamus, the rhinoKenyatherium, the giraffePalaeotragus,[8] the horseHipparion,[9] the elephant-like proboscideansDeinotherium and (possibly)Choerolophodon,[8] and thecolobine monkeyMicrocolobus.[10] The third premolar of a smallnyanzapithecine ape was also found in Nakali,[11][6] andSamburupithecus was nearly contemporaneous withNakalipithecus, and was discovered 60 km (37 mi) to the north of Nakali.[3]
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