On the presence of Arcellites disciformis Miner emend. Ellis & Tschudy (Salviniales), and other megaspores, from the Cenomanian of Patagonia, Argentina

SANTAMARINA, P. E.; BARREDA, V. D.; IGLESIAS, A.; VARELA, A.

Salvador

Congreso; XIV International Palynological Congress ? X International Organisation of Palaeobotany Conference; 2016

XIV International Palynological Congress ? X International Organisation of Palaeobotany Conference

We report here the first South American record of Arcellites disciformis from the Cenomanian Cerro Waringsection (S49°31?16.8?? - W71°29?07.7??), Mata Amarilla Formation, Santa Cruz Province, Argentina. Thistaxon corresponds to a heterosporous fern related to Salviniales on the bases of general morphologicalfeatures; it has been widely recorded from the Albian to the Cenomanian (Cretaceous) of North America,but there is no previous record for the Southern Hemisphere. The Mata Amarilla Formation consists of threelithostratigraphic members; the Lower and the Upper Members represent an estuarine paleoenvironmentdeveloped in a shallow marine embayment, and the Middle (radiometrically dated at 96.23 ± 0.71 Ma,middle Cenomanian) a fluvial setting. A. disciformis was recovered from the lower member associatedwith other megaspores assigned to Balmeisporites sp., and at least one other undetermined form. Thesemegaspores were analyzed under light and scanning electronic microscopes. The Patagonian specimensof Arcellites disciformis fit with the original diagnosis; they present a spherical spore body with pittedexoexine and several appendages, and a neck formed by six leaf-like appendages with crenulate margins.Arcellites has previous records only from the Albian of the Santa Cruz province, represented by four species:A. santacrucensis Baldoni, A. humilis Villar de Seoane & Archangelsky, A. pentagonalis Villar de Seoane &Archangelsky and Arcellites sp. A. This new record in the Cenomanian extends the stratigraphic distributionof Arcellites in the Austral Basin and enlarges the importance of these water ferns, probably related to anextinct family of Salviniales, in Late Cretaceous ecosystems of Patagonia; it also supports a bi-hemisphericdistribution for A. disciformis. New studies in yet unexplored areas would help to a better understanding ofthe evolutionary history of this important group of water ferns.