Diversification of heterosporous water ferns during the Late Cretaceous of Patagonia

DE BENEDETTI FACUNDO; MARÍA DEL C. ZAMALOA; GANDOLFO, MARIA A.; NÉSTOR R. CÚNEO

Tucson, Arizona

Conferencia; Botany 2019; 2019

Botanical Society of America

Heterosporous water ferns constitute a monophyletic group that includes two extant families: Marsileaceae and Salviniaceae. Marsileaceae comprises small, rooted ferns that are usually found on the margins of ponds, lakes, and rivers; whereas Salviniaceae includes small plants that are free floating and form extensive communities on the surface of low energy freshwater environments, such as swamps, ponds, and lakes. The fossil record of water ferns goes back to the Late Jurassic, although the group seems to have diversified highly during the Late Cretaceous together with the flowering plants. Recently, several aquatic fern remains (macro and microfossils) were reported from the Upper Cretaceous La Colonia Formation, Patagonia, Argentina, and some of them are the southernmost records for the group. In the light of new discoveries, we present a review of the megaspores and microspores related to both families. Marsileaceae is represented by Molaspora lobata, M. reticulata, and Crybelosporites cf. C. pannuceus while Salviniaceae by Azolla coloniensis, Azolla sp., Paleoazolla patagonica, cf. Azollopsis coccoides, and cf. Azollopsis intermedia. The spores were recovered from massive to finely laminated sediments, probably deposited by suspension in stagnant freshwater bodies. This spore assemblage is the most diverse so far known for South America and of the Southern Hemisphere, and it is clear evidence of the marked radiation of aquatic ferns at the end-Cretaceous worldwide.