REGNELLIDIUM (SALVINIALES, MARSILEACEAE) MACROFOSSILS AND ASSOCIATED SPORES FROM THE LATE CRETACEOUS OF SOUTH AMERICA

摘要

Premise of research. Fossils representing aquatic ferns with clear affinities to extant Regnellidium (Salviniales, Marsileaceae) are reported for the first time from Upper Cretaceous sediments of the La Colonia Formation, Chubut Province, Argentina. Methodology. Preserved organs including rhizomes bearing roots, compound leaves, and associated putative sporocarps were collected from the Cerro Bosta and Quebrada del Helecho localities of the La Colonia Formation. Spores were macerated for the macrofossil-bearing sediments of the Cerro Bosta locality and examined with SEM. Pivotal results. The macrofossils are morphologically similar to extant Regnellidium diphyllum. The fossil plants are rhizomatous, with the rhizomes bearing roots and leaves with two leaflets. The leaflets have 'dichotomizing venation and a marginal vein. Associated megaspores attributed to Molaspora lobata and microspores of the Crybeloporites type are also comparable to those of extant Regnellidium. Conclusions. These fossils represent the first report of Regnellidium-like macrofossils and the widespread Cretaceous megaspore taxon Molaspora from South America. Their presence in the La Colonia Formation suggests that Regnellidium may have been present on the continent continuously for more than 65 million years, although Cenozoic reports are necessary to confirm this hypothesis.