The fish assemblage associated with the Late Miocene Chadian hominid (Toros-Menalla, Western Djurab) and its palaeoenvironmental significance

摘要

Chad is a key region for understanding early hominid evolution and the related environmental changes of the Late Miocene. We present an extensive study of the freshwater ichthyofauna associated with Toumai, the oldest hominid known so far, at site 266 of the Late Miocene fossiliferous area of Toros-Menalla, northern Chad. Fish diversity was found to be relatively high and included at least 20 species: Polypteriformes, Polypteridae (Polypterus sp.); Osteoglossiformes, Osteoglossidae (cf. Heterotis niloticus), Mormyriformes, Gymnarchidae (cf. Gymnarchus niloticus); Cypriniformes, Cyprinidae (cf. Labeo sp.); Characiformes, Alestidae (Hydrocynus sp., Alestes/ Brycinus sp., Sindacharax sp., cf. Sindacharax sp. or Bunocharax sp.); Siluriformes Claroteidae (Clarotes sp., Auchenoglanis soye), Clariidae (two Clarias sp.), Mochokidae (two Synodontis sp.), and two Siluriformes indet.; Perciformes incertae sedis (Semlikiichthys darsao), Latidae (Lates niloticus); Tetraodontiformes Tetraodontidae (two Tetraodon sp.). Among the fossil taxa three belong to extinct genera, four to fossil species of extant genera, and two species (Semlikiichthys darsao and Auchenoglanis soye) are only known from Toros-Menalla. The Tetraodon from TM 266 is the oldest known in continental Africa. After estimating the taphonomic bias, we propose a reconstruction of the fossilised aquatic environment. This corresponds to a stream or a lake with open waters, vegetated bank and a flooding regime.