Professor of Geosciences, Pennsylvania State University
Fossil Plants and Global Change: The Past Can Save the Future
Abstract: Fossils directly reveal the responses of life through time to the dynamic Earth system, providing invaluable insights for the modern world. We make extensive, well-dated collections of fossil plants to investigate intervals of global change, concentrating on the ca. 20 million years encompassing the end-Cretaceous extinction and recovery followed by Paleocene-Eocene global warming. Fossil leaves with abundant, diverse insect-feeding damage show positive correlations of feeding intensity and diversity with temperature, a significant end-Cretaceous plant and insect extinction followed by a bizarre interval of decoupled plant and insect diversity, and the earliest records of several trophic associations. The significant responses of the plant-insect system to past temperature shifts are highly relevant to anthropogenic warming, whereas the suddenness and severity of the end-Cretaceous extinction make it an especially informative analog for modern extinctions. In Patagonia, Cretaceous to Eocene floras exhibit high biodiversity and rich biogeographic links to modern-day West Pacific rainforests via the ancient Gondwanan connection. Spectacular examples include early Eocene fossils of Eucalyptus (gums), Castanopsis (Asian chinquapin), and Agathis (kauris), all long extinct in South America due to post-Gondwanan cooling and aridification. Many Patagonian fossils are older than corresponding molecular age estimates and physically demonstrate Gondwanan history for their lineages. Fossils spotlight the need to conserve living analogs, and paleontological values contribute to the establishment of reserves around the world that protect living-fossil organisms, including World Heritage sites. However, the living rainforests that harbor the Gondwanan diaspora flora are under severe anthropogenic pressure. Southeast Asia faces the most severe extinction risks on the planet, yet its fossil history remains poorly known. To unravel the complex biogeographic origins of the region, we are engaged in new paleobotanical efforts in Malesia and areas that have contributed to its flora through earth-history events (Indochina, India-Pakistan, Patagonia, Australia). To propel this work, and to unlock a large sector of paleobotanical ‘dark data’ more generally, we are developing new computer vision tools to rapidly increase the quality and quantity of fossil-leaf identifications.