An emended diagnosis of Gangamopteris buriadica Feistmantel from the Permian of Gondwana

Abstract

This study aims mainly to revaluate the diagnostic characters of Gangamopteris (?) buriadica Feistmantel based on the analysis of the type material, housed at the collection of the Geological Survey of India, Calcutta, and other specimens, housed in distinct collections of southeastern (São Paulo, Rio de Janeiro) and southern Brazil (Porto Alegre). A recent reexamination of the type material revealed an unusual taphonomic feature which is characterized by the lateral folding of the leaf lamina under itself. This fact leads to a new interpretation of the leaf shape from a lanceolate-spathulate to a more ovate to obovate outline. Additionally, the partial view of the lamina hinders the observation of the true lateral veins pattern in their full extent, which inclines towards the lateral margins. As a consequence of this reinterpretation, we propose an amendment to the species original diagnosis, to include the curled lamina and lateral venation pattern of leaf margins as diagnostic characters of the species. Some specimens from the Early Permian strata of the Paraná Basin also show the same diagnostic characters and therefore have been included in this fossil-species. Consequently, the occurrence of G. buriadica Feistm. emend. is confirmed and extended to the Paraná Basin, being stratigraphically (e.g., Itararé Group and Rio Bonito Formation) and geographically (e.g., São Paulo and Rio Grande do Sul states) spread over southeast-southern Brazil. Finally, the taxonomic, taphonomic and ecological implications of the presence of curled leaves are briefly discussed.