Australopithecus bahrelghazali

Australopithecus bahrelghazali Temporal range: Middle Pliocene
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 a hominin species that inhabited the Bahr el Ghazal region in Central Africa around 3.6 million years ago. It was discovered in 1995 by a Franco-Chadian team led by the paleontologist Michel Brunet. All four fossils that have been found since 1995 are jaw (mandibular or maxillar) fragments.

A. bahrelghazali is the only australopithecine species found in Central Africa. It is also of great importance as it is the first fossil to show that there is a geographical "third window", that is, beyond East Africa and South Africa, of early hominin evolution. The locality is roughly 2,500 km (1,600 mi) west of the East African Great Rift Valley, making it far removed from what is broadly thought to be the "cradle" area of human evolution.

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. In 2008, the sediments the specimens were found in were radiometrically dated (using beryllium) to 3.58 million years ago. Another jawbone was discovered at the K13 site in 1997, and another from the KT40 site.

A. bahrelghazali was the first australopithecine recovered from Central Africa, and disproved the earlier notion that they were restricted to east of the Great Rift Valley 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.

The validity of this species has not been widely accepted given how few remains there are, with the remains that do exist being quite similar 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 thin 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

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. At the K12 site, the remains were found alongside the fossils of a large silurid catfish, a Geochelone tortoise, a Trionyx softshell turtle, a Tomistoma gharial, the elephant Loxodonta exoptata, a giraffe, the white rhinoceros Ceratotherium praecox, a Hipparion horse, a Sivatherium, antelope of which some were endemic, a Kolpochoerus afarensis pig, the hippo Hexaprotodon protamphibius, an anatid waterbird, and an otter. Some of these are also known from contemporary East African sites, implying that animals could freely migrate from east to west of the Great African Rift. This wildlife assemblage indicates a lakeside environment featuring perennial streams and a mosaic environment of gallery forest, wooded savanna, and open patches of grassland. 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.

Carbon isotope analysis indicates a diet of predominantly C₄ 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.

See also

• List of fossil sites (with link directory)
• List of human evolution fossils (with images)

Bibliography

• 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.
• Leakey, Mary; Walker, A (1997). Antiguos fósiles de homínidos en África. Investigación y Ciencia. p. 75.
• Reader, John (2011). Missing links. In search of human origins. New York: Oxford University Press. p. 538.

External links

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