Neogene is the second stage of the Cenozoic Era. It begins approximately 23 million years ago and ends 2.6 million years ago.
We can divide the Neogene into two stages:
Mioceno, starts 23M of years and ends 5’3M of years.
Plioceno, starts 5.3M of years and ends 2.6M of years.
The global climate of the Neogene is one of a decrease in temperatures at a global level, creating gradients between North and South and the beginning of the diversification of hot, temperate and cold climates. These are the first steps of the glaciation.
In the Miocene, there is a rapid evolution and adaptation of land animals to a new changing environment. The climate cools down more and more quickly, there is a drop in the level of the oceans, an increase in mountain ranges due to tectonic movements, part of the Earth freezes (in the Miocene the Antarctic begins to freeze, it could be indicated as “the first cooling stage” before the Quaternary glaciation) and the humid forests that were in areas far from the tropics are lost.
Large landscapes of grasslands and extensions of herbaceous plants with some trees appear, an early savannah where there used to be rainforests, forcing herbivores to evolve before two aspects: getting food and avoiding being food.
In the forests the plants were more watery and less hard, while now in the prairies the plants are harder because they have to retain water, so herbivores develop a series of adaptations such as a very specialized stomach in the case of ruminants, or much more specialized teeth to crush and grind the cellulose of the leaves in order to better extract their nutrients in the subsequent digestion.
But the problem that arises is that they are now much more exposed, not protected by dense vegetation. The herbivores become easier prey and a coevolutionary race of predator-prey survival begins (although it always existed, but now it becomes more striking in the case of mammals), in which the herbivores will develop defense systems (speed of escape, spikes, hard plates…) to avoid the carnivores, while the carnivores will do the same but in order to be able to hunt (sharper claws, stronger muscles, that are even faster…).
From this period are the first ruminants such as buffaloes and camels, as well as more specialized equines such as Merychippus.
One of the main origins of the change in climate and vegetation is due to plate tectonics. The continents move to positions very similar to the present ones, but some are still connected creating bridges of access to different areas, such as the connection between North and South America with Antarctica and Australia, and between Africa and Eurasia, allowing access and transport of large carnivores such as sabre teeth and also herbivores such as elephants, rhinos, equids and primates.
Together with the separation of Antarctica and its freezing, it allowed the flow of ocean water to change, causing the warm water of the Equator to cool down as it travelled to the South Pole and then to return to the Equator to warm up, creating a gradient from the equatorial zones to the polar zones, increasing the change in global temperature.
At the end of the Miocene only ice existed in Antarctica and mountain peaks, the rest of the continents did not yet begin to freeze, but they began to present a climatic variation (hot and arid climates near the equator of the globe, which became warmer as they approached the poles), but it was still a climate of warm temperature.
The climate of the Pliocene is cooler than that of the Miocene, dominated by savannahs and wide expanses of herbaceous plants. The global temperature is falling and the planet was getting colder, especially in parts of the Northern Hemisphere, when at the end of the Pliocene the frost and glaciers began to advance.
A very important fact of the Pliocene is the origin of the Panama Canal, a bridge connecting North and South America that did not exist in the Miocene, which led to the disappearance of almost all the marsupials in the southern subcontinent. North America was previously connected to Eurasia, but it allowed the exchange of placental species and its expansion. When North America separated from Eurasia, it soon joined South America, which implied new movements of placentals from the north to the south where marsupials were found, almost eradicating them as they were better prepared for such environments.
In general, the world was very similar to the present one but with less ice. Savannas became more abundant, and grasslands with herbaceous plants spread widely. This could have led to early hominids like the Austrolopithecus becoming more bipedal in their build, so that they could walk long distances in treeless grasslands. Some date Homo habilis, the first primate in the genus Homo, and we can indicate that it was the first clear ancestor of modern-day humans, at the end of the Pliocene and beginning of the Pleistocene, without reaching any agreement as to the point in time at which it originated (although recent data date it to around 2?4Ma, which introduces it to the Pleistocene).
In the Pliocene, there is also a great specialization of perissodactyls (placental ungulate herbivores with an odd number of hooves), among which we find horses, rhinos and tapirs, such as the reduction of the number of hooves towards the current single hooves as it is the case for current horses.
In the Pliocene, we begin to see that the central hoof of the perissodactyls acquires greater importance, supporting more weight than the rest. This can be observed because it increases in size with respect to the other two that become more vestigial.
One of the hypotheses on how the climate cooled down along the Neogene is that due to plate tectonics that gave rise to the formation of large mountain ranges such as the Himalayas because of the collision of the Indian and Eurasian plates, and together with the separation of South America-Antarctic-Australia, they produced a reorganization of the ocean currents and together with this a reorganization of temperatures throughout the globe.
Another hypothesis is an increase in the amount of gases that were released into the atmosphere due to the increase of forests in earlier times (Paleogene and early Neogene), which made our atmosphere more unstable and caused fluctuations throughout the Pliocene, which succumbed to a global cooling that would precede the subsequent Pleistocene ice age (early Quaternary).