First discovery of fossil dung beetle brood balls and nests in the ChadianPliocene Australopithecine levels

The Pliocene continental formations of the paleo-lake Chad system are known because of the recent discovery of the first australopithecine known west of the Rift Valley. The structures under study are found in sandstone level s associated with a rich fauna, including mammals, birds, reptiles and fish es. Analysis of the depositional environment and fauna indicates a mosaic l andscape of gallery forest, savannah, grassland and ephemeral rivers interr upted by lacustrine episodes. This sandstone facies contains bioturbation i n the form of sandstone balls 4-12 cm in diameter, slightly flattened at th e poles. These structures are characterized by an external husk or crust an d by a decimetric cavity in the upper part of the ball. Between the husk an d the cavity are a number of concave laminae similar to those of a bulb, wh ose concavity is directed toward the upper cavity. The comparison between t hese structures and the brood balls of modern Scarabaeidae shows great simi larity, especially in the external husk, the concave internal laminae and t he chamber of the grub in the upper part of the structures. This bioturbati un is interpreted as fossil brood balls of dung beetles (Coleoptera, Scarab aeidae). Fossil dung beetle brood balls are generally rare, but have been k nown since the 1940s. They can be very abundant in any series, as described by several authors in South America. The first fossil dung balls were desc ribed in this area in 1938 by Frenguelli and by Roselli. These authors desc ribe elementary spherical forms of 35 mm in diameter on average, flattened at the poles and with an upper cavity. The fossil dung beetle brood balls d iscovered in Chad are the first in which all the internal characteristic st ructures are preserved. Many of them are connected by a remarkably large ne t of tunnels which has no parallel in the past or the present.