 LD-350-1 mandible | |
| Common name | LD 350-1 |
|---|---|
| Species | Homo, species uncertain |
| Age | c. 2.775 million years |
| Place discovered | Afar,Ethiopia |
| Date discovered | 29 January 2013 |
| Discovered by | Chalachew Seyoum |
LD 350-1 is the earliest known specimen of thegenusHomo, dating to 2.75–2.8 million years ago (mya), found in theLedi-Geraru site in theAfar Region ofEthiopia. The specimen was discovered insilts 10 m (33 ft) above the Gurumaha Tuff section of the site[1][2] by Ethiopian palaeoanthropologist Chalachew Seyoum on 29 January 2013. It is currently unassigned to a species, and it is unclear if it represents the ancestor toH. habilis andH. rudolfensis which evolved around 2.4 mya.[1]
LD 350-1 is an adult left jawbone including thecanine, bothpremolars, and all threemolars. In terms of overall size, the specimen is within the range of what is seen in smallAustralopithecus afarensis specimens, and LD 350-1 seems to be atransitional form betweenAustralopithecus andHomo. However, the specimen's anatomy strongly diverges fromaustralopithecines and more closely aligns withHomo: themental foramina are not located on a depression, it has asymphyseal keel (a line of bone jutting out at the midline of the jaws), the jawbone maintains a more or less constant depth whereas it is deepest under the premolars in someAustralopithecus, and there are several differences regarding thetooth crowns. This specimen confirms thatHomo dental and jaw anatomy diverged from those ofAustralopithecus very early on. LD 350-1, like otherarchaic humans, seems to have lacked a distinct chin.[1]
The origin ofHomo 2.8–2.5 mya is accompanied by climatic changes, but because otherHomo specimens are not known from this time period, it is unclear if this was indeed the causal factor.[1] Because of the strong dental divergence exhibited in LD 350-1, it may be that the initial split was caused by a change in diet.[3] The KNM-ER 5431 specimen (comprising left and right premolars and the first two molars) fromKoobi Fora,Kenya, dating to 3–2.7 mya could represent the same species as LD 350-1. The discovery of such an earlyHomo specimen discredits some past hypotheses on the timing of theAustralopithecus/Homo transition, including deriving 2.6 mya fromA. garhi. It is unclear ifA. afarensis, which is known from the same region until 3 mya, was an ancestor to LD 350-1.[1] However, subsequent studies have suggested that the specimen also shares characteristics withAustralopithecus and that it is clearly distinct fromH. habilis.[4][5]
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In 2019, the earliestOldowan stone tools were discovered in Ledi-Geraru dating to 2.6 mya and may have been manufactured by the same species as LD 350-1. The invention of the sharp-edged Oldowan may be tied to unique biological changes inHomo. It is unclear if the Oldowan developed independently or from earlier, simpler australopithecine stone traditions (the only one identified is theLomekwiindustry). In either case, the transition to sharper tools would have allowed different feeding strategies and the ability to process a wider range of foods than australopithecine technology permitted, which would have been advantageous in the changing climate of the time.[6]
LD 350-1 lived in a much drier and more open environment thanA. afarensis typically inhabited.[3] Given the abundance ofgrazing animals the area was likely similar to modern day African open grasslands, such as theSerengeti or theKalahari; but the presence ofDeinotherium bozasi (abrowser) may indicategallery forests; andHippopotamus afarensis,crocodiles and fish indicate river and lake systems.[2]