New dicynodonts (Therapsida, Anomodontia) from the Early Triassic of Laos: implications for the tetrapod recovery after the Permian–Triassic mass extinction and the paleobiogeography of Southeast Asian Blocks
Résumé
The dicynodonts are an emblematic group of herbivorous therapsids, which have survived the
Permian–Triassic (PT) crisis. Laotian dicynodonts from stratigraphically well-constrained beds, using U–Pb
on zircon dating, bring new insights into terrestrial faunas of Southeast Asia during the Early Triassic. They
have already briefly been described but their phylogenetic relationships were never been investigated. Reexamination
of the Laotian dicynodonts, three well-preserved skulls, indicates that they belong to two new
species. Our phylogenetic analysis within Dicynodontia indicates that 1) gen. et sp. nov. 1 is closely related
to some ”Dicynodon ”- grade taxa; and 2) gen. et sp. nov. 2 is a stem taxon to Kannemeyeriiformes. The
phylogenetic affinities of these new Laotian dicynodonts allow to discuss about the recovery of the
terrestrial tetrapods during the Early Triassic: the survival of a Permian lineage across the PT crisis and/or a
rapid recovery with a new occurrence in the Early Triassic. The Laotian dicynodonts also shed new light on
the debated paleogeographic issues concerning the evolution of Southeast Asia from the late Paleozoic to
the early Mesozoic, particularly on the timing of the collision between the Indochina, the South China and
the North China blocks. The Early Triassic age of the two new Laotian dicynodonts, their essentially
terrestrial lifestyle, and the phylogenetic affinities between gen. et sp. nov. 2 and Early Triassic Chinese
Kannemeyeriiformes, suppose a land connection between the Indochina Block and other dicynodont
bearing continents as early as the Early Triassic.