Taoheodon baizhijuni, gen. et sp. nov. (Anomodontia, Dicynodontoidea), from the upper Permian Sunjiagou Formation of China and its implications

Abstract

ABSTRACT Recently, Repelinosaurus robustus from Laos was proposed as the basal-most member of Kannemeyeriiformes and regarded as Early Triassic in age. A new dicynodont specimen from the Sunjiagou Formation of Shanxi, China, is described and named as Taoheodon baizhijuni, gen. et sp. nov. It is characterized by autapomorphies such as a shallow fossa on a triangular region at the proximal side of the postorbital bar, a basisphenoid contribution to the basisphenoid-basioccipital tubera that slopes anterodorsally at a shallow angle, and the absence of a pterygoid keel. It is further differentiated from other dicynodontoids by the combination of characters such as a narrow median pterygoid plate, a pterygoid that does not contact the maxilla, an occipital condyle that is wide and arc-like in posterior view, and without a circular central depression or fossa, and the lateral dentary shelf that is thin but with distinct dorsal and ventral surfaces. A phylogenetic analysis recovers T. baizhijuni as sister taxon of the Laotian Counillonia superoculis plus Repelinosaurus robustus, a ‘core-Dicynodon’ clade that includes species from Africa, Russia, China, and Laos. Based on the current phylogenetic and geological evidence, the Laotian dicynodonts should be late Permian rather than Early Triassic in age. The migration route of the Laotian clade should have passed through the east margin of the South China Block.