Diverse Fossil Floras from the Paleogene of Patagonia, Argentina: Origins of High Plant and Insect Diversity in South America

0345750

Wilf

Tropical South America has the highest species richness in the world for many groups of terrestrial plants and animals, making this region a top priority for conservation. However, the history of this exceptional biodiversity is poorly understood because rock exposures in northern South America are limited by forest cover and deep weathering. Paleocene and early Eocene fossil floras from middle latitudes of Patagonia are invaluable resources for addressing this problem. Well exposed in modern desert outcrops, these assemblages represent humid subtropical vegetation from the southern reaches of the expanded Neotropical forests that existed during a globally warm time period. One of the most spectacular Patagonian floras comes from Laguna del Hunco (LH), an early Eocene (52 million years ago) site in Chubut Province, Argentina with outstanding preservation equal to the most famous North American Eocene floras, such as Florissant and Republic. In earlier efforts, the investigators recovered more than 155 plant species from fewer than 5,000 specimens. Fewer than 25% of these entities were previously known. Adjusted for sample size, this significantly exceeds the richness of Eocene floras from any other region, yet the potential exists for many more species to be found. On these fossil plants is preserved the highest diversity of well-preserved, insect-mediated leaf damage of any Cenozoic flora, including diverse and previously unrecorded examples of specialized feeding such as galls and mines. These early results support the hypothesis that South American hyperdiversity, usually attributed to relatively recent events of the last 2-10 million years, may have a considerably more ancient history. This study will examine floral diversity, plant and insect systematics, and plant-insect associations at LH and two other floras, one Eocene (Rio Pichileufu, Rio Negro Province) and one Paleocene (Salamanca, Chubut Province). Major questions to be addressed include: (1) Did high plant and insect-feeding diversity exist over a broad area of Paleogene Patagonia? (2) Was there a diversification of plants and insects from the Paleocene to the Eocene with global warming as seen elsewhere in the world? (3) What are the precise Neotropical and 'Australasian' affinities of the floras and their insect herbivores, and what is the importance of these affinities for understanding modern biotas?

The work is expected to have several beneficial impacts with regard to student training, international collaboration, and dissemination of results. Student participation will be central to all phases of the research from field to publication, including the major involvement of two female and one male Argentine doctoral students. The project is an international collaboration among diverse U.S. and Argentine specialists at a time of reduced scientific opportunity in Argentina. Primary inventory data will be permanently available to the research community through monographic treatments, Internet publication of data sets, and the deposition of specimens in the Argentine host repository. Illumination of the deep history of South American biodiversity is expected to have impacts on research and conservation efforts in South America today.