New species of osmundaceous fertile leaves from the upper Triassic of Argentina

Abstract

A new species of <i>Osmundopsis</i> Harris is described based on several impression-compression fossils from the upper section of the Potrerillos Formation (Uspallata Group) at Cerro Cacheuta Hill, Mendoza Province, Argentina. <i>Osmundopsis zunigai</i> sp. Nov. is characterized by having fertile pinnae with a slender striate rachis, bearing widely separate, opposite to subopposite short falcate pinnules with an entire margin, rounded apex, and a partially reduced lamina. The pinnules bear sporangia loosely disposed in clusters of four or five on the abaxial side. The sporangia are wedge-to heart-shaped, shortly stalked, with cells of the apical region thickened, and have a vertical dehiscence slit. The spores are trilete and laevigate. This is the first record of <i>Osmundopsis</i> in the Triassic of Argentina. The mutual occurrence or co-preservation of <i>Osmundopsis zunigai</i> sp. Nov. with sterile fronds of <i>Cladophlebis kurtzi</i> suggests the possibility that these species formed part of a dimorphic bipinnate frond. The diversity and geographic extent of fertile leaves of the <i>Osmunda</i> lineage in the early Late Triassic, with records in South Africa and Antarctica and now with this new taxon, support the idea of a moist mesothermal climatic belt in southern Gondwana.