The structures under study belong to the Pliocene continental formation of the palaeo-lake Chad system. This formation is famous for the discovery, in 1995, of the first australopithecine from Chad associated with a rich fauna of mammals, birds, reptiles and fishes. The analysis of this fauna and the interpretation of the depositional environment reveal a landscape of gallery forest, savannah grasslands, and ephemeral rivers interrupted by lacustrine episodes. The sandstone facies contains sandstone balls of 4 to 12 centimetres in diameter, lightly flattened at the poles. These structures are characterized by an external husk or crust and by a centimetric cavity in the upper part of the ball. Between the husk and the cavity, there exists a number of concave laminae, similar to those of a bulb, whose concavity is directed toward the upper cavity. These balls are associated with a vast metre-scale gallery network. This sandstone balls are interpreted as fossil brood-balls of dung beetles (Coleoptera, Scarabaeidae). Comparisons between these structures and the brood-balls of modern Scarabaeidae reveal great similarity, especially in the external husk, the concave internal laminae, and the chamber for the larva in the upper part of the structures.

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