Neogene Period

The Neogene Period lasted from 23.04 to 2.58 million years ago. It is the second period of the Cenozoic Era, between the Palaeogene and Quaternary, and contains the Miocene and Pliocene epochs. During its 20.46 million years, climate passed through a warm optimum and long cooling, grass-dominated open habitats expanded, ocean circulation changed, and early hominins appeared.

The Neogene is often described as the making of the modern world because many living families became conspicuous. That phrase needs caution. Sabre-toothed carnivorans, several proboscidean branches, giant ground sloths and many unfamiliar ungulates shared ecosystems with early members of modern groups.

Name, boundaries and stages

Neogene means “new-born” or “new recent”. It was introduced to distinguish younger Cenozoic faunas from the Palaeogene. Historical schemes extended it into the Pleistocene, but the current international chart ends the period at 2.58 Ma and assigns the Pleistocene to the Quaternary.

The lower boundary is defined in marine rocks near the first appearance of the foraminifer Paragloborotalia kugleri. The upper boundary coincides with the base of the Gelasian Stage and the Matuyama reversed-polarity chron. These independent markers help correlate marine and continental records.

The Miocene climate swing

Early Miocene climates warmed toward the Miocene Climatic Optimum around 17 to 15 Ma. Forests reached high southern latitudes and parts of coastal Antarctica supported tundra-like vegetation and low woodland. The Antarctic ice sheet persisted but changed in size and stability.

After the optimum, cooling resumed and Antarctic ice expanded. Later, Northern Hemisphere ice became increasingly important. Oxygen isotopes from marine shells combine signals from deep-water temperature and global ice volume, so models and independent evidence are needed to separate them.

Grass existed earlier, but landscapes changed

Grasses originated before the Neogene. The major change was the expansion of open grass-dominated biomes in many regions, especially during the later Miocene. C4 grasses, efficient under warm seasonal conditions and low carbon dioxide, became prominent in parts of Africa, Asia and the Americas.

High-crowned teeth, enamel isotopes, pollen, phytoliths and fossil soils record this transition. None alone maps a whole biome. A grazing tooth can reveal an individual’s abrasive diet, while local pollen may be carried from vegetation some distance away.

Miocene plains and preservation at Ashfall

Open woodlands and plains supported horses, rhinocerotoids, camelids, proboscideans and diverse carnivorans, with different combinations on each continent. Nebraska’s Ashfall Fossil Beds preserve animals that died after breathing and ingesting volcanic ash, many around a water source.

Mountains, continents and marine gateways

Continued uplift in the Himalaya, Tibetan Plateau, Andes and other ranges changed rainfall, erosion and regional habitats. Africa approached Eurasia, closing parts of Tethys and opening dispersal routes. Australia moved north, while South America remained isolated until late in the period.

Plate movement works with climate rather than as a single universal cause. Mountain building can create wet windward slopes, dry rain shadows and new river systems. Weathering can also remove atmospheric carbon dioxide over long timescales.

Neogene oceans

Baleen whales diversified as ocean productivity and circulation changed. Toothed whales included many extinct experiments. Pinnipeds spread through coastal habitats, while the giant shark Otodus megalodon hunted large marine vertebrates. Its maximum size remains model-dependent because the skeleton was cartilaginous and is known mainly from teeth and vertebrae.

The Messinian Salinity Crisis

Between about 5.97 and 5.33 Ma, restriction of Atlantic exchange transformed the Mediterranean. Thick gypsum and halite deposits record intense evaporation, while erosion surfaces and deep channels show large water-level changes. The basin did not simply become one completely dry desert for the entire interval.

At 5.333 Ma, Atlantic water again entered the Mediterranean at the start of the Zanclean. Erosion near Gibraltar supports a major inflow, but the precise rate and route are modelled from geology rather than directly observed.

Faunas on separate continents

Africa and Eurasia exchanged proboscideans, bovids, giraffoids, carnivorans and apes as connections changed. North America supported horses, camelids and pronghorn relatives. Long-isolated South America retained sloths, glyptodonts, native ungulates and terror birds. Australia continued its distinctive marsupial radiation.

The Isthmus of Panama and faunal exchange

The Central American connection developed progressively rather than appearing in one day. By the Pliocene, a continuous land route enabled the Great American Biotic Interchange. Proboscideans, cats, dogs and raccoon relatives moved south; sloths, armadillo relatives and porcupines moved north.

Restriction of ocean exchange also reorganised currents and salinity. Its role in Northern Hemisphere glaciation interacts with atmospheric carbon dioxide and orbital forcing and should not be treated as a lone switch.

Early hominin history

Hominins originated in Africa. Late Miocene and Pliocene fossils document varied combinations of upright walking, climbing, teeth and brain size. No fossil species is automatically a direct human ancestor; most belong somewhere on a branching tree.

The Laetoli trackway, about 3.66 million years old, directly records habitual bipedal walking by early hominins across wet volcanic ash. It does not preserve the walkers’ faces, exact species or social relationship.

How the record is tested

The transition at 2.58 Ma begins the Quaternary Period. It marks intensified Northern Hemisphere glaciation within a longer cooling trend, not the first appearance of ice or humans.