La séquence Plio-pléistocène d’Ain Boucherit-Ain Hanech (Algérie orientale): biochronologie, environnements, et comportements hominidés

Abstract

The Ain Boucherit-Ain Hanech research area in northeastern Algeria documents evidence of the earliest hominid presence in North Africa. The study area is rich with Plio-Pleistocene fluvio-lacustrine deposits. There are four main fossil and artifact-bearing localities, including Ain Boucherit (Q) and (R), Ain Hanech, and El-Kherba. Ain Boucherit occurrences are encased in Unit P/Q and R of the Ain Hanech Formation, while those from the localities of Ain Hanech and El-Kherba are located higher up in Unit T of the same formation. Normal geomagnetic polarity, evidenced in Units S and T, is correlated to the Olduvai subchron dated to 1.78-1.95 Million years ago (Ma). The stage of evolution of Kolpochoerus and the presence of Anancus suggest that Ain Hanech and El Kherba are dated to circa 1.78 Ma, corroborating the paleomagnetic correlation. The lower units P/Q and R are estimated to date between 2.0-2.3 Ma. The Acheulean material is contained in the calcrete deposits sealing the stratigraphic sequence. There are similarities and differences between the faunas of the different units of the Ain Hanech Formation. Important differences between the faunas from Ain Boucherit and Ain Hanech/El Kherba include the degree of evolution of its Equus and its increase in abundance in the upper levels, the species of large Bovini, the species of Alcelaphini (abundant Oreonagor at Ain Boucherit and abundant numidocapra at Ain Hanech and El Kherba), and the presence and abundance of the small antelope Parantidorcas at Ain Boucherit. The fauna from Unit R is similar to that of Unit Q. All faunas have several of the aquatic elements such as hippopotamus, aquatic turtles, crocodiles, frogs or fish. However, most elements are indicative of relatively dry or open habitats. The increase of abundance in equids and the decrease in small antelopes (Gazella and in particular Parantidorcas) suggest that the environment was more open in Ain Hanech and El Kherba. Furthermore, stable isotope analysis on pedogenic carbonate suggests that the El-Kherba stratigraphic profile may record change in organic matter input over time that is consistent with the general Plio-Pleistocene continental trend of increasing aridification and grassland expansion. In all the localities, the lithic artifact assemblages are primarily made of limestone and flint, and comprise core forms, debitage, and retouched pieces. The assemblages are Oldowan similar to those known at Olduvai Upper Bed I/Lower Bed II in Tanzania. Subsistence analysis indicates that Ain Hanech and El-Kherba hominids were responsible for modifying animal carcasses and documents for the first time evidence of early hominid large animal foraging capabilities in northern Africa during the Plio-Pleistocene.