Sedimentology and taphonomy of a tetrapod fossil accumulation in the Triassic Burgersdorp Formation of the Karoo Basin

Abstract

Field investigations of a rare accumulation of tetrapod fossils in the Triassic Burgersdorp Formation of the Karoo Basin reveal the palaeoenvironmental and behavioural mechanisms that led to its genesis. A total of 140 skulls and skeletons of seven tetrapod taxa and samples of three burrow cast geometries were collected with details of their depositional environment setting. These data are interpreted and integrated to reconstruct the palaeoenvironment and taphonomic pathways leading to accumulation, burial and preservation of this anomalous occurrence. The sedimentological facies analysis reveals a high sinuosity meandering river and floodplain setting. A semi-arid climate, with seasonal rainfall caused periodic rise and fall of the water table and floodplain ponds. Herbivorous tetrapods dominated by procolophonids, with dentitions adapted to browse fibrous reedbeds, congregated around pond margins. The animals scratch-burrowed in the floodplain surface for thermo-regulation and possibly estivation. Combined physical and behavioural factors caused the higher-than-average probability of tetrapod death, burial and preservation at this site