A BURROW CAST WITH LYSTROSAURUS SKELETAL REMAINS FROM THE LOWER TRIASSIC OF SOUTH AFRICA

We report on a large burrow cast with skeletal contents from Lower Triassic strata of the Palingkloof Member of the Balfour Formation, which forms the lowermost portion of the Lystrosaurus Assemblage Zone (LAZ) of South Africa. The burrow cast is similar to large burrow casts previously described from the LAZ that were identified as large-scale Scoyenia domichnia. It is the first large burrow cast from the LAZ found to contain diagnostic fossil bone. The burrow cast is a relatively straight, subhorizontal (inclined ∼12°), dorsoventrally compressed tube consisting of an entry ramp and living chamber; the entrance to the burrow is not preserved and there is no evidence that the ramp formed a spiral section. The skeletal material comprises a single, partial, disarticulated skeleton of a juvenile animal that can be assigned with confidence to the dicynodont genus Lystrosaurus. Whereas similar large-diameter burrow casts from strata slightly higher in the LAZ have been attributed to Lystrosaurus, we present an alternative hypothesis that a carnivorous tetrapod constructed the burrow. Our preferred hypothesis is supported by the observation that the interred Lystrosaurus skeleton is too small to be the maker of this particular burrow, by the general observation that carnivorous tetrapods construct relatively straight burrows, and by the partial, disarticulated state of the skeleton, which we interpret as the remains of larded prey. We suggest that akidnognathid theriodonts of the genera Moschorhinus or Olivierosuchus, the most conspicuous large predators of the LAZ, were the constructors of large-diameter, subhorizontal burrows.