Yaho (archeological site)

Yaho or Yayo is an archeological site 160 kilometers northwest of Koro Toro, Chad. In 1961, Yves Coppens excavated a partial hominin face and erected the taxon Tchadanthropus uxoris. Loxodonta atlantica were also discovered from the site.

Chronology
It is proposed that the middle of the Angamma delta bore Holocene strata dating to 1000 years in the lowest parts and up to 7300 years at the latest. Other parts of the formation reach up to 10,000 years.

Geology
The Angamma Delta is found within the area north of paleolake Megachad. The delta is very well preserved, standing up to 330m tall, as it can be observed sloping into a mudstone and diatomite-filled basin that drops 240m. The delta was fed by a braided fluvial distributary leading from the Tibesti Mountains from the north. They do not cut through the delta, suggesting that the braided rivers dried before the lake did. Delta sediment was visibly disturbed by waves from the lake, and the front was eroded, revealing other sediments within.

Its sediments are very exposed through a series of cliffs and canyons that run perpendicular from the delta. Underneath the delta are volcanic tuffs and breccias overlain with diatomite. The sediment is composed of silts and fine sand interspersed with thin intraformational conglomerates. Strata thicken nearer to the top and have distinct boundaries. It shows evidence of river flooding events that supplied sediment to the delta.

Discovery and Dating
On March 16, 1961, Yves Coppens' wife, Françoise Le Guennec, discovered a hominin fossil 11 kilometers from the western wall of the Angamma cliff and assigned the temporary name Tchadanthropus uxoris based on the country, lake of origin and honoring Le Guennec. Angamma cliff is located north of the west well of Yaho. In association with the hominin were fossils of Loxodonta atlantica, which Coppens suggested might place the hominin within the end Lower or early Middle Pleistocene.

In 1965, Marcel Bleustein organized a conference for the discovery, which scientists were very skeptical of. The press, however, were more interested in the implications of the discovery. The discovery of this fossil made Coppens media famous. Tobias (1973) states that the fossil is probably Homo erectus younger than one million years. In 2010, the specimen was given an updated age estimate of 900-700 kya. According to data proposed by Servant (1983), the specimen may be only 10 ka based on the geology of the site.

Description
The specimen may be a young individual based on the presence of a metopic suture, but this is also present in the adult Zhoukoudian XII so it may not be indicative of age. The face is broad and short, but because the upper jaw is so eroded, its entire height cannot be calculated. The vault is high and intermediate in curvature between Zhoukoudian, Chellean Man, and Australopithecus. Another possible testament to age is slight postorbital constriction. However, the frontal sinus is expanded, indicative of adulthood. The tori are heavier than australopiths but lighter than later hominins. The frontal process bears a posterior obliquity that might signify a high zygomatic root. The sockets are like those of Kabwe, large and rectangular. Substantial prognathism below the nose is present. There are no preserved tooth, but the incisor socket suggests that this tooth was small. No diastema is detected, and the nasal anatomy is like Solo. The brain capacity is difficult to calculate, but it may have been on the smaller end.

Classification
Originally, Coppens provisionally correlated the facial skeleton with australopiths. In 1966, he suggested that the face bore similarities with early and later hominins, thinking that it either represented a late australopith or early "pithecanthropine," probably closer to the latter. He also considered attribution to Homo habilis, which was a recent advancement at the time. He assigned the provisional name Tchadanthropus uxoris to the find, aware that the procedure was not diligent but rather standard in the field. His decision was made as a placeholder until greater understanding of human evolution could allow for taxonomic simplification. In 2017, Coppens admitted in an interview that the fossil was closer to H. erectus than an australopith. A less popular scientific name for the specimen is Homo uxoris. Most regard the specimen as a member of H. habilis or H. erectus. However, Wood (2002) notes that the prognathism may be a product of twisting seen in the fossil caused by winds causing an australopith-like appearance, which would prove Servant (1983)'s hypothesis that the specimen is only 10 ka.