Australopithecus bahrelghazali

Australopithecus bahrelghazali Temporal range: Piacenzian
Mandible of "A. bahrelghazali" (KT12 / H1)
KT12/H1 ("Abel") jawbone
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Primates
Suborder:	Haplorhini
Infraorder:	Simiiformes
Family:	Hominidae
Subfamily:	Homininae
Tribe:	Hominini
Genus:	†Australopithecus
Species:	†A. bahrelghazali
Binomial name
†Australopithecus bahrelghazali Brunet et al., 1995
Synonyms
Praeanthropus bahrelghazali

Australopithecus bahrelghazali is an extinct species of australopithecine discovered in Koro Toro, Bahr el Gazel, Chad, probably dating to 3.5–3 million years ago. It is the first and only australopithecine known from Central Africa, and demonstrated that this group was widely distributed across Africa as opposed to being restricted to Eastern and Southern Africa as previously thought. The validity of A. bahrelghazali has not been widely accepted, in favour of synonymising it with the contemporaneous A. afarensis from East Africa because of the anatomical similarity and the fact that A. bahrelghazali is known only from 3 partial jawbones and an isolated premolar. The specimens inhabited a lakeside grassland environment with sparse tree cover, and likewise predominantly ate C₄ savanna foods—such as grasses, sedges, storage organs, or rhizomes—and to a lesser degree also C₃ forest foods—such as fruits, flowers, pods, or insects.

Research history

In 1995, a jawbone preserving the premolars, canines, and the right second incisor (KT12/H1, "Abel") as well as an isolated first upper premolar (KT12/H2) were recovered from Koro Toro, Bahr el Gazel, Chad. They were discovered by the Franco-Chadian Paleoanthropological Mission, and reported by French palaeontologist Michel Brunet, French geographer Alain Beauvilain, Breton anthropologist Yves Coppens, French palaeontologist Emile Heintz, Chadian geochemist engineer Aladji Hamit Elimi Ali Moutaye, and British palaeoanthropologist David Pilbeam. Bahr el Gazel means "River of the Gazelles" in Classical Arabic. Based on the wildlife assemblage, the remains were roughly dated to the middle to late Pliocene 3.5–3 million years ago, so the describers preliminarily assigned the remains to Australopithecus afarensis which inhabited Ethiopia during that time period, barring more detailed anatomical comparisons. In 1996, they allocated it to a new species A. bahrelghazali, denoting KT12/H1 as the holotype and KT12/H2 a paratype. Another jawbone was discovered at the K13 site in 1997, and another from the KT40 site. In 2008, a pelite recovered from the same sediments as Abel was found by radiometrically dated (using the ¹⁰Be/⁹Be ratio) to have been deposited 3.58 million years ago. However, Beauvilain responded that Abel was not found in situ but at the edge of a shallow gulley, and it is impossible to figure out from what stratigraphic section the specimen (or any other fossil from Koro Toro) was first deposited in in order to accurately date it.

A. bahrelghazali was the first australopithecine recovered from Central Africa, and disproved the earlier notion that they were restricted to east of the eastern branch of the East African Rift which formed in the Late Miocene. Koro Toro is situated about 2,500 km (1,600 mi) from the Rift Valley, and the remains suggest australopithecines were widely distributed in grassland and woodland zones across the entire continent. The lack of other Central and West African australopithecines may be due to sampling bias as similarly aged fossil-bearing sediments are more or less unknown beyond East Africa. In 2014, the first australopithecine in the western branch of the East African Rift was reported in Ishango, Democratic Republic of the Congo.

At present, the classification of Australopithecus and Paranthropus species is in disarray. Australopithecus is considered a wastebasket taxon whose members are united by their similar physiology rather than close relations with each other over other hominin genera. In an attempt to resolve this, in 2003, Spanish writer Camilo José Cela Conde and evolutionary biologist Francisco J. Ayala proposed splitting off the genus "Praeanthropus" and including A. bahrelghazali alongside Sahelanthropus (the only other hominin known from Chad), A. anamensis, A. afarensis, and A. garhi.

The validity of A. bahrelghazali has not been widely accepted given how few remains there are and how similar they are to A. afarensis.

African hominin timeline (in mya)
View references

Anatomy

The teeth of KT12/H1 are quite similar to the jawbone of A. afarensis, with large and incisor-like canines and bicuspid premolars. Unlike A. afarensis, the alveolar part of the jawbone where the tooth sockets are is almost vertical as opposed to oblique, poorly developed superior transverse torus and moderate inferior torus (two ridges on the midline of the jaw on the tongue side), and thin enamel on the chewing surface of the premolars. Brunet and colleagues had listed the presence of 3 distinct tooth roots as a distinguishing characteristic, but the third premolar of the A. afarensis LH-24 specimen from Middle Awash, Ethiopia, was described in 2000 having the same feature, which shows that premolar anatomy was highly variable for this species. The mandibular symphysis (at the midline of the jaw) of KT40 especially as well as KT12/H1 have the same dimensions as the symphysis of A. afarensis, though theirs is relatively thick compared to the height.

Palaeoecology

Carbon isotope analysis indicates a diet of predominantly C₄ savanna foods, such as grasses, sedges, storage organs, or rhizomes. The smaller C₃ portion may have comprised more typical ape food items such as fruits, flowers, pods, or insects. This indicates that, like contemporary and future australopiths, A. bahrelghazali was capable of exploiting whatever food was abundant in its environment, whereas most primates (including savanna chimps) avoid C4 foods.

During the Pliocene around the expanded Lake Chad (or "Lake Mega-Chad"), insect trace fossils indicate this was a well-vegetated region, and the abundance of rhizomes may suggest a seasonal climate with wet and dry seasons. Koro Toro has yielded several large mammals, including several antelope of which some were endemic, the elephant Loxodonta exoptata, the white rhinoceros Ceratotherium praecox, the pig Kolpochoerus afarensis, a Hipparion horse, a Sivatherium, and a giraffe. Some of these are also known from contemporary East African sites, implying that animals could freely migrate between east and west of the Great African Rift. The K13 site features, in regard to bovids, an abundance of Reduncinae, Alcelaphinae, and Antilopinae, whereas Tragelaphini is much rarer, which indicates an open environment which was drier than contemporary East African sites. In total, the area seems to have been predominantly grasslands with some tree cover. In addition, the area featured aquatic creatures including predominantly catfish, and also 10 other kinds of fish, the hippo Hexaprotodon protamphibius, an otter, a Geochelone tortoise, a Trionyx softshell turtle, a Tomistoma gharial, and an anatid waterbird. These aquatic animals indicate Koro Toro had open-water lakes or streams with swampy grassy margins, connected to the Nilo-Sudan waterways (including the Nile, Chari, Niger, Senegal, Volta, and Gambia Rivers).

See also

• African archaeology
• Ardipithecus ramidus
• Australopithecus anamensis
• Australopithecus afarensis
• Australopithecus deyiremeda
• Kenyanthropus
• List of fossil sites (with link directory)
• List of human evolution fossils (with images)

Further reading

• Beauvilain, Alain (2003). Toumaï, l'aventure humaine. Paris: La Table Ronde. p. 239.
• Gibbons, Ann (2006). The first human, the race to discover our earliest ancestors. New York: Doubleday. p. 306.
• Reader, John (2011). Missing links. In search of human origins. New York: Oxford University Press. p. 538.

External links

• Australopithecus bahrelghazali, Abel
• Human Timeline (Interactive) – Smithsonian, National Museum of Natural History (August 2016).