The Neogene: When Earth’s Forests Yielded to Grasslands

Space · Published 31 October 2026 Swipe more like this →

In short: During the Neogene, a massive environmental shift transformed the planet's landscape. As global cooling took hold, vast forests were replaced by expansive grasslands and savannahs. This dramatic change didn't just alter the scenery; it forced a radical evolutionary pivot for mammals, birds, and marine life alike.

The Neogene Period, spanning from 23 million to 2.6 million years ago, is defined by significant geological and climatic transitions. It is divided into two primary epochs: the Miocene (roughly 23 to 5.3 million years ago) and the Pliocene (roughly 5.3 to 2.6 million years ago). This era was marked by a general cooling trend that led to more distinctive latitudinal biotic zones and the gradual closing of the Tethys Sea as continents drifted into their modern configurations.

One of the most profound changes was the replacement of forests with grasslands and savannahs. This shift created entirely new ecological niches, favoring animals that could adapt to grazing on grass rather than browsing in meadows. For example, horses transitioned from forest-dwelling browsers to grassland grazers. This period also saw a surge in biodiversity; whales diversified in the oceans, while sharks reached their largest recorded sizes during the Miocene. In the seas, the first known kelp forests appeared as ocean circulations shifted to form large gyres.

The Pliocene specifically showcased these trends toward cooler and drier environments. While terrestrial records suggest a drying trend, marine data from 3.0–3.5 million years ago indicate a relatively warm interval in the North Atlantic. On land, mastodons underwent great evolutionary diversification to suit various habitats, while camels and horses became abundant across different regions. Although faunas in Eurasia and North America showed striking similarities, there was little evidence of direct migration between the two continents during this time.

Ultimately, the Neogene served as a crucible for modern biology. The combination of continental separation and climate cooling drove complex patterns of mammalian evolution, leading to the rise of many of the more modern mammals we recognize today.

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