| Australopithecus deyiremeda | |
|---|---|
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| Jaw reconstruction ofA. deyiremeda. At the top, theholotypemaxilla BRT-VP-3/1 (shown reversed), while at the bottom is theparatypemandible BRT-VP-3/14. | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Primates |
| Suborder: | Haplorhini |
| Infraorder: | Simiiformes |
| Family: | Hominidae |
| Subfamily: | Homininae |
| Tribe: | Hominini |
| Genus: | †Australopithecus |
| Species: | †A. deyiremeda |
| Binomial name | |
| †Australopithecus deyiremeda Haile-Selassieet al., 2015 | |
| Synonyms | |
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Australopithecus deyiremeda is anextinctspecies ofaustralopithecine fromWoranso–Mille,Afar Region, Ethiopia, about 3.5 to 3.3 million years ago during thePliocene. Because it is known only from three partial jawbones, it is unclear if these specimens indeed represent a unique species or belong to the much better-knownA. afarensis.A. deyiremeda is distinguished by its forward-facing cheek bones and smallcheek teeth compared to those of other earlyhominins. It is unclear if a partial foot specimen exhibiting a dextrous big toe (a characteristic unknown in any australopithecine) can be assigned toA. deyiremeda.A. deyiremeda lived in a mosaic environment featuring both open grasslands and lake- or riverside forests, and anthropologist Fred Spoor suggests it may have been involved in the KenyanLomekwistone-toolindustry typically assigned toKenyanthropus.A. deyiremeda coexisted withA. afarensis, and they may have exhibitedniche partitioning to avoidcompeting with each other for the same resources, such as by relying on different fallback foods during leaner times.
Australopithecus deyiremeda was first proposed in 2015 by Ethiopian palaeoanthropologistYohannes Haile-Selassie and colleagues based on jawbone fossils from the Burtele and Waytaleyta areas ofWoranso–Mille,Afar Region, Ethiopia. Theholotype specimen, a young adult leftmaxilla with all teeth except the firstincisor and thirdmolar BRT-VP-3/1, was discovered on 4 March 2011 by local resident Mohammed Barao. Theparatype specimens are a complete adultbody of the mandible with all incisors BRT-VP-3/14, and an adult right toothless jawbone WYT-VP-2/10, which were discovered by Ethiopian fossil hunter Ato Alemayehu Asfaw [es]. A right maxilla fragment with the fourthpremolar BRT-VP-3/37 was found 5 m (16 ft) east of BRT-VP-3/14, and it is unclear if these belonged to the same individual. The sediments wereradiometrically dated to 3.5–3.3 million years ago, theMiddle Pliocene.[1]
The describers believed the remains were distinct enough from the contemporary and well-knownA. afarensis to warrant species distinction, andA. deyiremeda is counted among a growing diversity ofLate Plioceneaustralopithecines alongsideA. afarensis,A. bahrelghazali andKenyanthropus platyops. The namedeyiremeda derives from theAfar language meaning "close relative" because, existing so early in time, the discoverers consideredA. deyiremeda to have been closely related to future australopiths.[1] However, though the proposed distinguishing characteristics are apparentlystatistically significant, given how few specimens ofA. deyiremeda exist, it is unclear if this indeed warrants species distinction or if these specimens simply add to the normal range of variation forA. afarensis. If it is a valid species, then it could possibly indicate someA. afarensis specimens are currently classified into the wrong species.[2][3]
Haile-Selassie and colleagues noted that, though it shares many similarities with the robustParanthropus, it may not have been closely related because it lacked enlarged molars which are characteristic ofParanthropus.[4]
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Despite being so early, the jaws ofA. deyiremeda show some similarities to those of the laterHomo andParanthropus. The jaw jutted out somewhat (prognathism) at perhaps a 39-degree angle, similar to most other earlyhominins. The cheekbone is positioned more forward than mostA. afarensis specimens. UnlikeAustralopithecus afarensis but likeParanthropus, the walls of thecheek teeth are inclined rather than coming straight up. The uppercanines are proportionally smaller than those of otherAustralopithecus, but are otherwise morphologically similar to those ofA. anamensis. The cheek teeth are quite small for an early hominin, and the first molar is the smallest reported for an adult Pliocene hominin. Nonetheless, theenamel was still thick as other early hominins, and the enamel on the second molar is quite high and more similar toP. robustus. The jawbone, though small, is robust and more similar to that ofParanthropus.[1]
In 2012, a 3.4-million-year-old partial foot,BRT-VP-2/73, was recovered from Woranso–Mille. It strongly diverges from contemporary and later hominins by having a dextrous big toe like the earlierArdipithecus ramidus, and consequently has not been assigned to a species.[5] Though more diagnostic facial elements have since been discovered in the area, they are not clearly associated with the foot.[1]
A. deyiremeda features a strong jawbone and thick enamel, consistent with a diet of toughsedges and similar foods which australopiths are generally thought to have primarily subsisted upon. The enamel on the upper incisor, canine and first premolar exhibitshypoplasia, probably caused by a period of malnutrition or illness duringenamel growth in infancy while the teeth were still growing.[6]A. deyiremeda was likely ageneralist feeder.A. deyiremeda andA. afarensis may have exhibitedniche partitioning given they cohabited the same area. That is, given dental and chewing differences, they may have had different dietary and/or habitat preferences, unless these differences were simply a product ofgenetic drift.[2][7] Much likechimpanzees and gorillas which have more or less the same diet and inhabit the same areas,A. deyiremeda andA. afarensis may have shared typical foods when in abundance, and resorted to different fallback foods in times of food scarcity.[3]
TheLomekwistone-toolindustry from northern Kenya is loosely associated with the Middle PlioceneKenyanthropus based on an upper jaw fragment assigned toKenyanthropus based on forward cheekbones, three-rooted premolars, and a small first molar. Since these features are also exhibited inA. deyiremeda, anthropologist Fred Spoor suggested thatA. deyiremeda was actually present at the site.[7] Identified at 3.3 million years old, the Lomekwian is the earliest culture. These knappersflaked off pieces ofcores made ofbasalt,phonolite andtrachyphonolite.[8] They held the core with one hand and struck it vertically with ahammerstone, which is a simple process, though more complex than the tool-making behaviours of non-human primates.[9]
The Middle Pliocene of Woranso–Mille featuresgrazingimpalas,alcelaphins, andelephants, as well asbrowsinggiraffes,tragelaphins, and forest-dwellingmonkeys. The feet of thebovid species do not seem to be specialised for any particular type of ground (such as wet, pliable, or hard), and the teeth of hoofed species indicates an equal abundance of grazers, browsers and mixed feeders. These suggest a mixed environment which features both open grasslands as well as forests probably growing on a lake- or riverside. Similar mosaic landscapes were inhabited byA. anamensis andA. afarensis who seem to have had no preferred environment.[10]
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