Abstract

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.

You do not currently have access to this article.