New dicynodonts (Therapsida, Anomodontia) from near the Permo-Triassic boundary of Laos: implications for dicynodont survivorship across the Permo-Triassic mass extinction and the paleobiogeography of Southeast Asian blocks

International audience; The dicynodonts are an emblematic group of herbivorous therapsids that survived the Permo-Triassic (P-Tr)crisis. Laotian dicynodonts from stratigraphically constrained beds, recently dated using the U-Pb zircon method, yield newinsights into terrestrial faunas of Southeast Asia during the latest Permian and earliest Triassic. Summarily described, theywere originally attributed to the genus Dicynodon. We provide a new phylogenetic analysis for Laotian dicynodonts, basedon three well-preserved skulls, indicating that they belong to two new taxa: Counillonia superoculis, gen. et sp. nov., andRepelinosaurus robustus, gen. et sp. nov. Our phylogenetic analysis of Dicynodontia indicates that (1) Counillonia is closelyrelated to some ‘Dicynodon’-grade taxa and (2) Repelinosaurus is a kannemeyeriiform. The phylogenetic affinities of thesenew Laotian dicynodonts allow discussion of the survivorship of multiple lineages (Kannemeyeriiformes and ‘Dicynodon’-grade dicynodontoids) across the P-Tr crisis. The Laotian dicynodonts also shed new light on the paleobiogeography ofSoutheast Asia from the late Paleozoic to the early Mesozoic, particularly the timing of collisions between the Indochina,the South China, and the North China blocks. The presence of dicynodonts in Laos, most likely in the Early Triassic, thusimplies that the connection between the Indochina Block and the South China Block occurred no later than the latestPermian or earliest Triassic (i.e., when the dicynodonts provide direct evidence for a connection).