A fertile Dicksoniaceae in the Eocene beds of King George Island, Antarctic Peninsula

Abstract

A fertile pinnule is described to King George Island, South Shetland Islands, northern Antarctic Peninsula. Preserved by its adaxial side, it shows a straight raquis that bears alternate and falcate segments where a unique oval and marginal sori appears in the upper margin, tridimensionally preserved. These morphological characters allow the association of this form with the modern genus Dicksonia L. Hérit. (Dicksoniaceae). It is the first record of fertile ferns of this genus to this island and to the Cenozoic of Antarctic Peninsula, where it was only known by sterile fronds and dispersed spores. Dicksonia related forms were registered on other islands of the western Antarctic Peninsula during the Lower Cretaceous and after the beginning of the Cenozoic, are exclusive from the King George Island. The sample comes from restricted levels composed by reworked volcanic grains deposited in shallow lakes, in a thick lava succession that was attributed to the Viéville Glacier Fm., Point Hennequin Group and considered as Eocene in age. The associated taphoflora is composed of other kinds of ferns, angiosperms dominated by Nothofagus, and Araucariaceae and Podocarpaceaea conifers. Nowadays Dicksonia is a relictual tree fern that grows in the rain forests coincident with the highlands created by the Gondwana drift-apart.

Key words: Dicksoniaceae, King George Island, Antarctic Peninsula, Middle Eocene.