Thaumatopteris paucipinnata sp. nov. (Gleicheniales): First fertile Dipteridaceae from the Middle Triassic of Southwestern Gondwana

Abstract

In the present study, a morphological and systematic analysis is carried out on fossil leaves of Dipteridaceae from the Don Raúl Member, Cortaderita Formation, Sorocayense Group, Middle Triassic, Cuyana Basin, in the southwestern region of San Juan Province, west-central Argentina. The examined specimens are preserved as impressions–compressions. The material is assigned to a new species of the genus Thaumatopteris and consists of sterile leaves with petiole, rachis, well-preserved pinnae, and dispersed fragments of monomorphic fertile leaves with leptosporangiate sporangia grouped into rounded sori and positioned on the abaxial surface. Thaumatopteris paucipinnata sp. nov. is characterized by small leaves, few pinnae per leaf, absence of a central pinna, triangular elongated secondary segments with entire margins, hexagonal areoles, and 5–6 sporangium per sorum. Although the morphology of the new species combines features of both Dictyophyllum and Thaumatopteris, their overall traits are more consistent with the latter. Until now, fertile Dipteridaceae leaves had only been found from the Late Triassic onward; therefore, the specimens described here represent the oldest known record.