New gymnospermous woods from the Permian of the Parnaíba Basin, Northeastern Brazil, Part I: Ductoabietoxylon, Scleroabietoxylon and Parnaiboxylon

New gymnospermous woods from the Permian of the Parnaíba Basin, Northeastern Brazil, Part I: Ductoabietoxylon, Scleroabietoxylon and Parnaiboxylon