The Neogene Period spanned from approximately 23.03 million years ago (Ma) to about 2.58 Ma. It represents the second of three periods within the Cenozoic Era, following the Paleogene and preceding the current Quaternary Period. Scientists divide the Neogene into two epochs: the Miocene (23.03 Ma to 5.33 Ma) and the Pliocene (5.33 Ma to 2.58 Ma). This timeframe was characterized by global transformations in both the planet’s physical landscape and the evolution of life.
Earth’s Dynamic Transformation
During the Neogene Period, Earth’s continents continued their slow drift, moving closer to their present-day configurations. This tectonic activity led to the formation and uplift of major mountain ranges. The Indian subcontinent’s collision with Asia contributed to the Himalayas, while the Alps emerged as Italy moved northward. The Pyrenees also formed, alongside significant uplift in the Rocky Mountains and Andes.
The ancient Tethys Ocean progressively closed, severing its eastern connections in two phases (around 20 Ma and 14 Ma). This closure contributed to shifts in ocean circulation and influenced global climate patterns.
The formation of the Isthmus of Panama, a land bridge that emerged late in the Pliocene Epoch, approximately 2.8 to 4 million years ago. This geological connection between North and South America reshaped oceanic circulation. It cut off the warm ocean currents that previously flowed between the Pacific and Atlantic Oceans.
The formation of this land bridge intensified the Gulf Stream, directing more warm water northward. This alteration, combined with other factors, contributed to a global cooling trend underway since the Paleogene. As the Neogene progressed, polar ice caps expanded, leading to a drop in global sea levels and setting the stage for subsequent glacial periods.
Life’s Terrestrial Journey
The changing Neogene environment influenced terrestrial life, leading to evolution and diversification, particularly among mammals and birds. A significant ecological shift was the widespread expansion of grasslands, which increasingly replaced vast forested areas, especially in the Northern Hemisphere. This expansion was driven by the cooler and drier climatic conditions.
The proliferation of grasses created new food sources and habitats. This spurred the evolution of grazing mammals, which adapted to consume these plant resources. For example, ancestors of modern horses transitioned from a browsing diet in forests to grazing on grasslands, developing specialized teeth for grinding tough grasses.
The Neogene saw a diversification of large grazing mammals, including early forms of horses, rhinos, and elephants, alongside their predators. While small grazing mammals were present, by the Late Miocene, medium to large-sized grazers became prevalent. This evolutionary response to the expanding grasslands created dynamic ecosystems across continents.
This period also marks a pivotal time in the evolution of primates, including the emergence of early hominids. Early apes, for instance, evolved from monkeys in Africa around 20 million years ago. More significantly, the fossil record indicates that hominins, the group that includes human ancestors, began to appear in Africa approximately 6 to 7 million years ago.
By the Pliocene, early hominids, such as Australopithecus afarensis (famously represented by “Lucy”), are found in African deposits. The earliest documented representatives of the genus Homo, such as Homo habilis, appeared toward the very end of the Neogene, around 2.8 to 2.4 million years ago, showcasing the beginning of bipedal locomotion.
Oceans Teeming with New Life
Marine ecosystems also underwent substantial changes during the Neogene Period, with a notable diversification of marine mammals. Various groups of whales, dolphins, seals, walruses, and sea cows evolved and spread, adapting to the shifting oceanic conditions. These adaptations allowed them to thrive in new environments and exploit different food sources.
Sharks, already ancient inhabitants of the oceans, continued to evolve and diversify. Many modern shark species can trace their lineage back to the Miocene and Pliocene Epochs. The Miocene, in particular, was a time when some sharks reached immense sizes, including the formidable Otodus megalodon, one of the largest predatory sharks known to have ever lived. The distinctive hammerhead sharks also evolved during the Cenozoic, with their appearance possibly occurring within the Neogene.
Coral reefs, important centers of marine biodiversity, experienced periods of significant development during the Neogene, particularly due to the flourishing of Scleractinia corals. However, these ecosystems were also affected by the period’s environmental changes. For example, Caribbean coral faunas experienced accelerated rates of both extinction and the emergence of new species between 4 and 1 million years ago, indicating dynamic shifts in their communities. The Miocene also saw the appearance of the first kelp forests, creating new complex habitats in coastal waters.
Changes in ocean currents played a significant role in shaping marine biodiversity and distribution. These changes affected nutrient distribution, water temperatures, and migratory routes, contributing to the distinct marine ecosystems observed today.