Carbon isotope evidence for CAM photosynthesis in the Mesozoic

Crassulacean acid metabolism (CAM) photosynthesis, a flexible adaptation to water-stress, has not been shown to occur before the Pleistocene, despite suggestions that CAM first evolved in the Mesozoic or earlier. Here we report on multiple (>= 7) positive organic carbon isotope excursions (delta C-13(org) > -20%) in Late Triassic and Early Jurassic (c. 200 Ma) sedimentary rocks from an arid terrestrial ecosystem in South Africa. These excursions are interpreted as evidence of the episodic dominance of CAM plants in response to heightened aridity in the heartland of Gondwana, and hint at climatic instability in a greenhouse world.