Oral Paper

         Paleobotany

First Nothofagus fossil cupules and fruits from South America, earliest Oligocene of northern Patagonia

Presenting Author
Ari Iglesias
Description
Nothofagus fossil pollen, leaves, and woods are abundant in Patagonia, but until now, no reproductive macrofossils have been known, obscuring information about the histories of the subgenera and the appearances of the many types of Nothofagus-dominated forests. Globally, fossil Nothofagus fruiting structures are only known from the Oligocene and Miocene of Tasmania, representing subgenus Lophozonia and two other subgenera. The cooling trend during the late Eocene - early Oligocene transition in southern South America generally correlates with a northward expansion of micro- and mesothermal taxa, but the timing of Nothofagus-dominated forests reaching northern Patagonia remains poorly understood. A new fossil macroflora, informally the “Prem site,” found in northern Patagonia (41° south latitude) is U-Pb dated to ~33.5 Ma, the first from South America that correlates precisely to the first half million years of the Oligocene and the Oi-1 glaciation. The assemblage is dominated by Nothofagus leaves (70 % of   ̴1000 leaf specimens), along with a low-diversity angiosperm and conifer flora. Abundant Nothofagus cupules and fruits (nuts) were found (20 cupules and 30 nut specimens). Three winged fruits are present (two trimerous and one dimerous) on some closed cupules. Many cupules show four well-developed valves, each with several rows of prominent ramified lamellae with multiple-tipped glands, and three fruit scars are visible on the inner cupule base. These features are diagnostic of the subgenus Lophozonia, which is currently distributed in northern Patagonia, Tasmania, New Zealand, and Australia. Other cupules from the Prem site have entire lamellae and different sizes and shapes, which may indicate the presence of other Nothofagus subgenera. The new fossils represent the first record for Nothofagus reproductive structures from South America. Furthermore, the abundant leaves indicate the earliest macrofossil record of a Nothofagus-dominated forest in northern Patagonia, supporting a northward expansion of the genus associated with global cooling and the Oi-1 glaciation.