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

ARI IGLESIAS; PATRICIO SANTAMARINA; AUGUSTO VARELA; VIVIANA BARREDA

San Salvador de Bahia

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

We report here the first South American record of Arcellites disciformis from the Cenomanian Cerro Waring section (S49º31?16.8??-W71º29?07.7??), Mata Amarilla Formation, Santa Cruz Province, Argentina. This taxon corresponds to a heterosporous fern related to Salviniales on the bases of general morphological features; 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 three lithostratigraphic members; the Lower and the Upper Members represent an estuarine paleoenvironment developed 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 associated with other megaspores assigned to Balmeisporites sp., and at least one other undetermined form. These megaspores were analyzed under light and scanning electronic microscopes. The Patagonian specimens of Arcellites disciformis fit with the original diagnosis; they present a spherical spore body with pitted exoexine 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 distribution of Arcellites in the Austral Basin and enlarges the importance of these water ferns, probably related to an extinct family of Salviniales, in Late Cretaceous ecosystems of Patagonia; it also supports a bi-hemispheric distribution for A. disciformis. New studies in yet unexplored areas would help to a better understanding of the evolutionary history of this important group of water ferns.