Figure 1.

Comparative time courses over most of the Phanerozoic of: (a) estimated atmospheric [CO₂] predicted from a geochemical model of the carbon cycle (GEOCARBSULF, adapted from Berner [13]) and multiple proxies of [CO₂] (stomatal indices and isotope analysis of liverworts, palaeosols, marine boron, phytoplankton and B/Ca, updated from the compilation of Royer [21]), with a dashed line at 1000 ppm indicating the atmospheric [CO₂] above which photosynthesis is saturated in most modern plants [22]; (b) estimated maximum stomatal conductance (adapted from Franks & Beerling [23]), estimated vascular species richness (adapted from Knoll & Niklas [24]), stomatal density (redrawn from Royer et al. [20]), Devonian and Carboniferous leaf size (adapted from Osborne et al. [25]), C₄ grass clade richness (adapted from Edwards et al. [9]) and angiosperm vein density (adapted from Brodribb & Feild [26]), all of which are expressed relative to the maximum value in the individual records of each parameter from the cited studies.