Abstract

Intensive exploration of the northern borders of the ancient Magallanes Basin resulted in the discovery of a Maastrichtian tidally-controlled delta system at Las Chinas - Cerro Guido complex with 20 km of outcrops and five plant-bearing units containing Nothofagus leaf imprints, associated with and underlying partiallyarticulated hadrosaur remains. The presence of Nothofagus, key genus of the modern sub Antarctic forests of Oceania and South America, is the oldest record of the genus in the Americas, and is interpreted to indicate a terrestrial connection between South America and the Antarctic Peninsula, leading to an exchange of terrestrial biota. The abundance of Nothofagus in Maastrichtian sediments in the Magallanes basin of Chile is interpreted here to provide evidence for floral exchange during-the Maastrichtian. Unfortunately, the physical evidence for these intermittent bridges is lost today due to subduction at the southwestern margins of Gondwana. However, the geographic continuity of Patagonia and the Antarctic Peninsula, currently disjointed by the Drake Passage, may partly explain the vicariant pattern and areas of endemism, although weather patterns differing between the western and eastern side of the isthmus may also have been important. We hypothesize that Nothofagus-dominated flora, previously successful in Antarctica, successfully invaded Patagonia during the Late Maastrichtian, and could explain the record of ornithopods in Maastrichtian rocks of Antarctica. The formation of land bridges during the Maastrichtian may be causally related to a cool episodes and consequent fall in sea level.