A new taxa for dipteridaceae fronds from the paso flores formation, late triassic, Neuquén basin, Argentina

Abstract

Steril and fertil fronds of dipteridacean ferns from the Paso Flores Formation (Norian) at Cañadón de Pancho area (Neuquén Basin, Argentina) are described. The morphological characteristics are: fanshaped 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 simple, whereas tertiary veins dichotomized and forming irregularly polygonal areoles. Sori 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. Sori are round in outline, each sorus consists of 45-60 or more sporangia. Mixed maturation of sporangia. The annulus of the sporangia is oblique and complete. These specimens share some morphological features of the fronds with the fossil genera Clathropteris Brongniart, 1828, Digitopteris Pott and Bomfleur, 2018, Thaumatopteris Goeppert, 1841 and, with some species of the Dictyophyllum Lindley and Hutton, 1834 as well as in the character soral, with one the current species of Dipteris Reinwardt. The Paso Flores specimens comprise an interesting mixture of features showing a unique combination that do not fit in the circumscription of any of the known and most abundant genera of Dipteridaceae. Thus, these fossil dipterid fern fronds suggest that they belong to a new taxonomic entity.