Salviniales from the Late Cretaceous of the Golfo San Jorge Basin

- Maastrichtian Salviniales are reported from the Golfo San Jorge Basin.
- A new species of Azolla is described in the Lago Colhué Huapi Formation.
- Azolla is diversified in the uppermost levels of the Chubut Group.
- Marsileaceaephyllum is recorded for the first time in Argentina.
- The plant fossils in the Lago Colhué Huapi Formation indicate freshwater conditions.

The freshwater ferns (Salviniales) are well represented in the Maastrichtian deposits of Cerro de los Fragmentos in the headwaters of the Río Chico, Golfo San Jorge Basin. The fossil material of Salviniaceae includes complete megaspore apparatuses with attached microspore massulae and dispersed megaspores, float systems and microspore massulae of Azolla. The new species Azolla colhuehuapensis displays distinctive morphological characters including relative small megaspore apparatuses with easily detached floats and usually attached eglochidiate massulae. The Marsileaceae are represented by the megaspore Molaspora lobata, microspores of Crybelosporites and vegetative remains of Marsileaceaephyllum sp. The assemblage also includes zygospores of the green filamentous algae Zygnemataceae, spores of Marchantiophyta and Monilophyta (Schizaeales), megaspores of Isoetalean affinity and Palm-type angiosperm pollen grains. All these organic microfossils and the associated palynomorphs indicate the presence of a freshwater environment where abundant water ferns were developing and reproducing.