A new species of Pleuromeia (Lycopsid) from the upper Middle Triassic of Northern China and discussion on the spatiotemporal distribution and evolution of the genus

Pleuromeia Corda is an iconic lycopod genus in the Early Triassic floras of the world. Pleuromeia fossils are very significant in stratigraphy and palaeoenvironmental interpretation and have been regarded as an important Lower Triassic index fossil. Although some recent studies show that the genus occurred in the lower part of the Middle Triassic, no definite Pleuromeia has been reported from the late Middle Triassic and the younger strata so far. In this paper, some reproductive organ fossils of Pleuromeia from the upper Middle Triassic Tongchuan Formation in Shaanxi Province (belonging to the Ordos Basin), North China, are described for the first time, belonging to the new species Pleuromeia obovata Deng nov. sp. Highly accurate dating results of tuff layers indicate that the age of the new species is between 241.06 ± 0.12 Ma and 241.558 ± 0.093 Ma, equivalent to the early Ladinian. This is the youngest species of genus Pleuromeia so far. Spatiotemporal distribution of Pleuromeia indicates that the genus first appeared in the Induan (Early Triassic) in North China, occurred widespread and flourished in both Laurasia and Gondwana during the Olenekian (late Early Triassic), declined from the Anisian (early Middle Triassic), survived in the Ladinian in North China, and may have gone extinct as early as the end of the Middle Triassic. North China may well have included the place of origination and the last habitats of this genus.