HOW GRASSY WERE LATE PLEISTOCENE HABITATS AT RANCHO LA BREA?: FIRST PHYTOLITH RECORDS FROM THE TAR PITS

Past reconstruction of Late Pleistocene habitat, vegetation types and animal diet at Rancho La Brea (RLB) have been based on dental microwear, mesowear, carbon isotope records from bone collagen and enamel, and analysis of vegetative remains in boluses extracted from herbivore cheek teeth. Together, these records have suggested that habitat and herbivore diets consisted mostly of C3 plants, with woody plants making up a majority of the diet in at least Bison and Camelops. Furthermore, though largely understudied, the macrobotanical record of the RLB deposits has yielded only a handful of grass fossils, suggesting that grass biomass may have been low at the site. But, given that paleobotanical remains from RLB have been largely under-collected and under-studied, the question of how much grass was present during the Late Pleistocene remains unanswered. Therefore, we present new records of vegetation from well-preserved, fossil phytoliths extracted from the asphaltic sediments of Rancho La Brea. Although preliminary, our results suggest that C₃ pooid grasses were a dominant component of the herbaceous plant cover in deposits dating between 55-40kya, and that C₄ PACMAD grasses were present, but extremely rare in agreement with carbon isotope data from tooth enamel. Future phytolith work aims to track changes in grass composition and biomass throughout the Late Pleistocene and Holocene, and to incorporate modern reference collection material to identify grass species to understand more fully the past biomes inhabited by the Rancholabrean megafauna.