Was Araucaria Sec. Eutacta living in Eocene Patagonia? Systematic revision of Araucaria pichileufensis indicates an Australasian rainforest connection .

ROSSETTO, GABRIELA; ESCAPA, IGNACIO; WILF, PETER

Rochester

Congreso; Botany 2018; 2018

Botanical Society of America

The iconic conifer genus Araucaria was prolific worldwide during the Mesozoic, but it has been restricted to the Southern Hemisphere since the Early Paleogene. During the early Cenozoic, globally warm climate and a close connection between South America, Antarctica, and Australia allowed for Araucaria to flourish in trans-Antarctic rainforests. Biotic interchange through this southern corridor continued until Antarctic separation and cooling began in the mid-late Eocene, causing large shifts in the genus? distribution that are still apparent in its modern biogeography. Of the nineteen living species of Araucaria, fifteen belong to Section Eutacta, restricted to Australasia. Characters that diagnose Sec. Eutacta include differentiation of leaves into juvenile and adult states, univeined leaves with curved apices, and samara-like bract-scale complexes with a single seed embedded in the tissues. The remaining three sections of Araucaria are divided between Australia, Papua New Guinea, and South America. Although it has been reported, it remains unclear what the evolutionary age and history of Eutacta are in Gondwanan South America due to lack of multiple organ preservation in the fossil record to definitively diagnose the section. Araucaria pichileufensis Berry 1938 fossils from Patagonia have the potential to greatly clarify Eutacta?s evolutionary timeline. This fossil species is abundant from Laguna del Hunco (LH; 52.2 Ma) and Rio Pichileufu, Argentina (RP; 47.8 Ma), two exceptionally diverse and well-dated Eocene rainforest floras recovered from fossil caldera lake deposits in the modern-day steppe of Patagonia. These fossil floras represent vegetation that was present before opening of the Drake Passage and thus include lineages that evolved prior to the final break up of Gondwana. Araucaria pichileufensis was described from its type locality RP 80 years ago, but its apparent relation to Australasian Eutacta species has not been tested with modern phylogenetic methods. Large new collections of A. pichileufensis including leafy branches, bract-scale complexes, and pollen cone organs represent the most complete multi-organ fossil preservation of Eutacta and provide the first strong fossil evidence that Australasian Sec. Eutacta once had a South American history. The objectives of this research are to use systematics and phylogenetics to test for the evolutionary relationships of the fossils with living Araucaria and to examine how a Gondwanan connection, and subsequent Antarctic isolation, may have been critical in shaping the modern distributions of the genus.