Gerardo Cladera

Early Cretaceous riparian vegetation in Patagonia, Argentina

Early Cretaceous riparian vegetation in Patagonia, Argentina. An autochthonous plant as-semblage found at the Bajo Grande locality, Anfiteatro de Tico Formation, Baquero Group, Early Aptian of Santa Cruz province, Argentina, is described. Sedimentological data show an alternation of sandstone and lime-stone, with recurrent fossil levels associated to a fluvial system. The frequent flood in areas close to the levee had an influence on the vegetation growing along the banks of the channels. A plant assemblage composed of Ricciopsis grandensis nov. sp. (bryophyte), Adiantopteris tripinnata nov. sp., Schizaeaceae pinnules (ferns), and the gnetalean fructification Ephedra verticillata nov. sp. was found in this paleoenvironment. The taphonomical studies suggest that the plant assemblage was autochthonous, and it grew and was buried in an area near a levee. This result is congruent with environmental data provided by living representative of the fossil taxa analyzed.

A new early angiosperm leaf from the Anfiteatro de Ticó Formation (Aptian), Santa Cruz Province, Argentina

A new record of angiosperm from Aptian deposits of the Anfiteatro de Tico Formation (basal unit of the Baquero Group), in its type locality, north-center of Santa Cruz province, Argentina is reported. This record integrates the fossiliferous level Williamsonia-Zamites that contains abundant remains of bennettite leaves and was deposited in floodplain facies. The fossil consists of a single leaf imprint, with entire margin and festooned brochidodromous venation of low rank. It has features that define, in part, the nymphaeaphyll morphological type. This type occurs among the most early assemblages having angiosperms (northeastern Brazil, Portugal, South Australia, eastern North America), and is part of a physiognomic-foliar pool associated to taxa considered to be basal within the group. This foliar morphotype, is found in some members of extant angiosperms of usually herbaceous habit, and perhaps, by analogy, this may have been the original habit of our fossil species. The mega floristic record of eocretaceous angiosperms from Southern Hemisphere is scarce. In spite of them, angiosperm foliar remains from other location (Bajo Tigre) of the Anfiteatro de Tico Formation are known. They are different to this new record. This incipient diversity suggests an even (pre-Aptian) presence of the angiosperms in the region.