Fig. 3.

Record of vegetation changes in the North American continental interior based on phytolith assemblages (represented as pie charts) compared with previous work. Areas with oblique hatched pattern represent timing of the spread of grass-dominated habitats according to phytoliths; the height of the areas reflects the degree of uncertainty in timing for each region due to missing data and problems with relative and absolute age assignment (marked as black dashed arrows bracketing phytolith assemblages). Inferred dates for the spread of grasslands from other lines of evidence [macrofossils and palynomorphs, ungulate faunas, and paleosols, respectively (1)] are marked as thick gray lines. “Open/closed(?)-habitat grasses” indicates grasses with unknown autecology but potentially related to pooids or PACCAD grasses [e.g., chionochloids (29)] (Fig. 2F).