Reniformichnus katikatii (New Ichnogenus and Ichnospecies): Continental Vertebrate Burrows from the Lower Triassic, Main Karoo Basin, South Africa

The formal ichnotaxonomic assignment of a new ichnogenus and ichnospecies, Reniformichnus katikatii, is presented based on the holotype and several field specimens from the Lower Triassic Katberg Formation in the main Karoo Basin of South Africa. The holotype is an inclined, burrow cast with bilobate base and reniform cross-section. Its width ranges from 12.6 to 14.7 cm, and its height is 5 to 7.4 cm resulting in an aspect ratio of 1.89 to 2.74. The surface preserves 70–180 mm long ridges running parallel to the long axis of the burrow on the upper parts of the walls and lower parts of the dorsum and shorter ridges (average length ∼27 mm) are preserved on the more ventral areas in two opposite orientations, cross-cutting each other in a rhomboid pattern. Burrow fills are passive and consist of slightly bedded, laminated, or massive clastic rocks that are coarser than the host mudstones. The burrow casts are isolated, never occurring in clusters. This simple burrow shows no evidence for branching, spiralling, interconnected tunnels, burrow linings, terminal chambers, or entrances. Preserved in fluvial floodplain mudstone units, the burrows were passively filled by layered, laminated, or massive sand and other coarser clastic sediments. The burrow casts are morphologically similar to unnamed Antarctic ichnotaxa that have been attributed to tetrapods (e.g., therapsids, procolophonids), extending the geographic range of the potential producers of Reniformichnus isp. to continental settings in southern Gondwana. Biostratigraphic evidence on the temporal distribution of Reniformichnus isp. suggests that the trace maker emerged in the aftermath of the Permo-Triassic mass extinction event to successfully burrow throughout the Early Triassic.