Eupolypod ferns with dryopteroid/thelypteroid traits from Arroyo Chacay (Huitrera Formation, Eocene), Río Negro Province, Argentina

Abstract

The Huitrera Formation is a sequence of volcanic deposits that outcrops in the northwestern region of Patagonia. Several paleofloras have been recognized in this (or in coeval) units, in classical localities named Pichileufu, Confluencia, Pampa de Jones and Laguna del Hunco. These works, focused mostly on the angiosperm and conifer content of the unit, allowed the recognition of a diverse array of taxa. Nevertheless, ferns remain underrepresented in the literature. In this work, three ferns preserved as impressions/compressions are described for this unit, collected from outcrops at the Arroyo Chacay locality. A new genus and species (Tapelrayen helgae gen. et sp. nov.) is designated to encompass fertile remains comparable with Thelypteridaceae and Dryopteridaceae. Another fossil form of ambiguous affinities is left in open nomenclature (Eupolypod incertae sedis) and a third form is referred to Cyclosorus sp. cf. C. interruptus (Willd.) H.Itô of the Thelypteridaceae. A discussion on the complex taxonomical scenario that is presented for fossil leaves comparable with Thelypteridaceae and Dryopteridaceae is presented, in light of the recent published taxonomic schemes.