First report of Cordaixylon Grand'Eury in the Permian of South America, Parnaiba Basin, Brazil

摘要

We describe the morphology and anatomy of cordaitalean tree stems preserved in Cisuralian lacustrine deposits of the Pedra de Fogo Formation, Permian of the Parnaiba Basin, northeastern Brazil. The remains consist of seven samples of petrified stems with septate pith (Artisia type) and preserved primary and secondary xylem. The anatomical features of these specimens support their classification in the genus Cordaixylon Grand'Eury, 1877, which is the first evidence of this genus not only in South America, but also in Gondwana. The sedimentological indicators suggest climatic seasonality during the deposition of the Pedra de Fogo unit. However, on a local scale, this area may have had a humid to sub-humid regional climate due to the presence of a large lacustrine system, which would allow these plants to grow in similar habitats to their locations in the Northern Hemisphere. The Parnaiba Basin contains a relatively high number of endemic taxa, but this genus is typical of the Euramerican Province and occurs in at least two areas of this basin. The presence of these trees and some forms of tree-ferns that are also shared with the Euramerican Province suggests the existence of a phytogeographic connection consisting of dispersal through a landscape linkage between the Euramerican tropics and northern Gondwana in the Late Pennsylvanian. This would make it possible for species to migrate between these two floristic provinces, a hypothesis that can be confirmed through further taxonomic and geological data. Finally, the presence of Cordabcylon in the Pedra de Fogo Formation can be considered indicative of a Cisuralian age for these rocks.