The Cenozoic is divided into three periods: the Paleogene, Neogene, and Quaternary; and seven epochs: the Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene.

The common use of epochs during the Cenozoic helps palaeontologists better organise and group the many significant events that occurred during this comparatively short interval of time.

Archaic mammals filled the world such as creodonts (extinct carnivores, unrelated to existing Carnivora).

This disrupted ocean currents worldwide and as a result caused a global cooling effect, shrinking the jungles.

[23] The Miocene Epoch spans from 23.03 to 5.333 million years ago and is a period in which grasses spread further, dominating a large portion of the world, at the expense of forests.

The Pliocene featured dramatic climatic changes, which ultimately led to modern species of flora and fauna.

The Isthmus of Panama formed, and animals migrated between North and South America during the great American interchange, wreaking havoc on local ecologies.

[25][26] The Quaternary spans from 2.58 million years ago to present day, and is the shortest geological period in the Phanerozoic Eon.

Many animals evolved including mammoths, giant ground sloths, dire wolves, sabre-toothed cats, and Homo sapiens.

100,000 years ago marked the end of one of the worst droughts in Africa, and led to the expansion of primitive humans.

As the Pleistocene drew to a close, a major extinction wiped out much of the world's megafauna, including some of the hominid species, such as Neanderthals.

Australia-New Guinea, having split from Pangea during the early Cretaceous, drifted north and, eventually, collided with Southeast Asia; Antarctica moved into its current position over the South Pole; the Atlantic Ocean widened and, later in the era (2.8 million years ago), South America became attached to North America with the isthmus of Panama.

[33] In the Cretaceous, the climate was hot and humid with lush forests at the poles, there was no permanent ice and sea levels were around 300 metres higher than today.

When South America became attached to North America creating the Isthmus of Panama around 2.8 million years ago, the Arctic region cooled due to the strengthening of the Humboldt and Gulf Stream currents,[35] eventually leading to the glaciations of the Quaternary ice age, the current interglacial of which is the Holocene Epoch.

Recent analysis of the geomagnetic reversal frequency, oxygen isotope record, and tectonic plate subduction rate, which are indicators of the changes in the heat flux at the core mantle boundary, climate and plate tectonic activity, shows that all these changes indicate similar rhythms on million years' timescale in the Cenozoic Era occurring with the common fundamental periodicity of ~13 Myr during most of the time.

From a geological perspective, it did not take long for mammals to greatly diversify in the absence of the dinosaurs that had dominated during the Mesozoic.

The ranges of many Cenozoic bird clades were governed by latitude and temperature and have contracted over the course of this era as the world cooled.

[40] Grasses also played a very important role in this era, shaping the evolution of the birds and mammals that fed on them.

Evolving in the Cenozoic, the variety of snakes increased tremendously, resulting in many colubrids, following the evolution of their current primary prey source, the rodents.

The Cenozoic is full of mammals both strange and familiar, including chalicotheres, creodonts, whales, primates, entelodonts, sabre-toothed cats, mastodons and mammoths, three-toed horses, giant rhinoceros like Paraceratherium, the rhinoceros-like brontotheres, various bizarre groups of mammals from South America, such as the vaguely elephant-like pyrotheres and the dog-like marsupial relatives called borhyaenids and the monotremes and marsupials of Australia.

[41][42] Cenozoic calcareous nannoplankton experienced rapid rates of speciation and reduced species longevity, while suffering prolonged declines in diversity during the Eocene and Neogene.

Diatoms, in contrast, experienced major diversification over the Eocene, especially at high latitudes, as the world's oceans cooled.