A new taxon for Dipteridaceae fronds from the Paso Flores formation, late Triassic, Neuquén basin, Argentina

Abstract

Sterile and fertile fronds of dipteridacean ferns from the Paso Flores Formation (Norian) at Cañadón de Pancho area (Neuquén Basin, Argentina) are described. The morphological characteristics are: fan-shaped fronds dissected in two equal and opposite rachial arms; each rachial arm bearing more than 18 primary segments. The primary segments fused up to 1/3 of the total length of the preserved lamina, and the remaining part is free, linear-lanceolate in shape, showing ondulate to deeply dissected lobes margins (less than 2/3 in length of the secondary vein). Primary and secondary veins are simple, whereas tertiary veins dichotomized and forming irregularly polygonal areoles. Sori are exindusiate, arranged in two regular rows on either side of the primary veins, as well as on both sides of the base of the secondary veins. They are round in outline; each sorus consists of 45-60 or more sporangia. The annulus of the sporangia is oblique and complete. These specimens share some morphological features of the fronds with the fossil genera Clathropteris, Digitopteris, Thaumatopteris and, with some species of the Dictyophyllum as well as in the soral features with one of the current species of Dipteris. The Paso Flores specimens comprise an interesting mixture and unique combination of features that differ from any of the known and most abundant genera of Dipteridaceae. Thus, these dipterid fossil fern fronds suggest that they belong to a new taxonomic entity.