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What fossil evidence shows that savanna-like vegetation existed in South America about 20 million years ago?

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Flat savanna plain with scattered acacia trees under a partly cloudy sky in Serengeti National Park, Tanzania. — Savanna A savanna marked with acacia trees in Serengeti National Park, Tanzania. Africa's Serengeti Plain is commonly used as an example of the savanna biome—a hot, seasonally dry ecological region characterized by an open tree canopy (i.e., scattered trees) above an understory of continuous grasses.

The South American fossil record provides evidence that well-developed, grass-rich vegetation—considered equivalent to modern savanna—was established in the region by the early Miocene Epoch, approximately 20 million years ago.1

While specific fossilized plant remains are often used to reconstruct ancient environments, studies of fossilized pollen in sediments from various sites in South America, Africa, and Australia provide strong support for the expansion of these seasonally dry habitats over time. This shift toward savanna-like vegetation occurred as global climates cooled during the Cenozoic Era, leading to reduced precipitation and the subsequent retreat of forests in midlatitude regions.1