An austral fern assemblage from the Upper Cretaceous (Campanian) beds of Cerro Guido, Magallanes Basin, Chilean Patagonia

Abstract

The Campanian–Maastrichtian succession of Cerro Guido, Southern Chile, is known by its plant fossils, vertebrates bones, including those of dinosaurs, and marine faunas that can be critical in the better understanding of the processes involved in the Western Gondwana break-up in the southernmost paleolatitudes and their effects over life, paleoclimate and paleogeography. As part of the retroarc foreland deposits of the Magallanes or Austral Basin, the Upper Cretaceous rocks from Tres Pasos and Dorotea formations, source of the fossil ferns here discussed, are exposed at the southern side of the Cerro Guido hill. The leaves of pteridophytes were identified in a macroflora dominated by primitive angiosperms, conifers and Taeniopteris, where they represented a secondary component of the understory. The data obtained show terrestrial fern populations, dominated by Cladophlebis, the cosmopolitan ‘Mesozoic’ taxa, accompanied by forms related to Alsophila, Alamatus, and the extant genus Anogramma, similarly to other Southern Hemisphere areas, and especially with those from the lower Upper Cretaceous of New Zealand. Their scarcity in the Upper Cretaceous assemblages of the Tres Pasos and Dorotea formations supports the inferred near-coastal environmental context and contrasts with their abundance and diversity in the Aptian to Coniacian deposits of the northern Antarctic Peninsula. Additional evidence suggesting that these remains were remobilized corroborates with the idea that they are a part of the vegetation that grew around interdistributary rivers or bays.