Fossil pollen records reveal a late rise of open-habitat ecosystems in Patagonia.

The timing of major turnovers in terrestrial ecosystems of the Cenozoic Era has been largely interpreted from the analysis of the assumed feeding preference of extinct mammals. For example, the expansion of open-habitat ecosystems (grasslands or savannas) is inferred to have occurred earlier in Patagonia than elsewhere because of the early advent of high-crowned teeth (hypsodont) mammals ∼26 Ma ago. However, the plant fossil record from Patagonia implies another evolutionary scenario. Here we show that the dominance of key open-habitat species--amaranths, Ephedra, asters and grasses--occurred during the last 10 Ma, about 15 Ma later than previously inferred using feeding/habitat ecology of extinct mammals. This late rise of open-landscapes in southern South America brings into question whether the expansion of open-habitat vegetation could have been the prime factor of high-crowned mammal diversification.