Lycopodiopsids and equisetopsids from the Triassic of Quebrada de los Fósiles Formation, San Rafael Basin, Argentina

In the late 1960s, rests of a low-diversity flora dominated by the lycopsid Pleuromeia were reported. The specimens were recovered from a creek near San Rafael, Mendoza Province, western Argentina, in the lower section of the Puesto Viejo Group, the Quebrada de los Fósiles Formation, considered as Early Triassic in age. Despite the importance of this flora with respect to the end-Permian mass extinction event, it was not yet described nor illustrated. Since then, the age of the Puesto Viejo Group has been revised and the Quebrada de los Fósiles Formation is now considered to be early Middle Triassic. The fossil plants are here first described and interpreted. The most common element, Pleuromeia cf. sternbergii, a species known worldwide that characterizes the post-extinction flora recovery, is accompanied by sphenopsids such as Neocalamites and Equisetostachys, and an herbaceous lycopsid. This community grew up associated with transient water bodies in flood plain environments that developed under warm temperate, strongly seasonal climatic conditions. The landscape was stressed by volcanism, and the conjunction of these factors probably restricted the colonization and development of a full ecosystem, as happened worldwide after the end-Permian mass extinction.