66 - 0 million years ago
The Cenozoic Era (// or //; also Cænozoic, Caenozoic or Cainozoic // or //; meaning "new life", from Greek καινός kainos "new", and ζωή zoe "life") is the current and most recent of the three Phanerozoic geological eras, following the Mesozoic Era and covering the period from 65 million years ago to present day.
The Cenozoic is also known as the Age of Mammals, because the extinction of many groups allowed mammals to greatly diversify.
Early in the Cenozoic, following the K-Pg event, the planet was dominated by relatively small fauna, including small mammals, birds, reptiles, and amphibians. From a geological perspective, it did not take long for mammals and birds to greatly diversify in the absence of the large reptiles that had dominated during the Mesozoic. Some flightless birds grew larger than the average human. These species are sometimes referred to as "terror birds," and were formidable predators. Mammals came to occupy almost every available niche (both marine and terrestrial), and some also grew very large, attaining sizes not seen in most of today's terrestrial mammals.
Climate-wise, the Earth had begun a drying and cooling trend, culminating in the glaciations of the Pleistocene Epoch, and partially offset by the Paleocene-Eocene Thermal Maximum. The continents also began looking roughly familiar at this time and moved into their current positions.
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 Quaternary Period was officially recognized by the International Commission on Stratigraphy in June 2009, and the former Tertiary Period was officially disused in 2004 because of the necessity to divide the Cenozoic into periods more like that of the previous Paleozoic and Mesozoic eras.[why?] The common use of epochs during the Cenozoic helps paleontologists better organize and group the many significant events that occurred during this comparatively short interval of time. There is also more detailed knowledge of this era than any other because of the relatively young strata associated with it.
The Paleogene spans from the extinction of the dinosaurs, some sixty six million years ago, to the dawn of the Miocene twenty three million years ago. It features three epochs: the Paleocene, Eocene and Oligocene.
The Paleocene ranged from 65 million to 55 million years ago. The Paleocene is a transitional point between the devastation that is the K-T extinction, to the rich jungles environment that is the Early Eocene. The Early Paleocene saw the recovery of the earth. The continents begin to take their modern shape, but all continents (and India) are separated from each other. Afro-Eurasia is separated by the Tethys Sea, and the Americas are separated by the strait of Panama, as the isthmus has not yet formed. This epoch features a general warming trend, with jungles eventually reaching the poles. Archaic mammals filled the world such as creodonts and early primates that evolved during the Mesozoic, and as a result, there was nothing over 10 kilograms. Mammals are still quite small.
The Eocene Epoch ranged from 55 million years to 33 million years ago. In the Early-Eocene, life was small and living in cramped jungles, much like the Paleocene. There was nothing over the weight of 10 kilograms. Among them were early primates, whales and horses along with many other early forms of mammals. At the top of the food chains were huge birds, such as Gastornis. It is the only time in recorded history that birds ruled the world (excluding their ancestors, the dinosaurs). The temperature was 30 degrees Celsius with little temperature gradient from pole to pole. In the Mid-Eocene, the circum-Antarctic current between Australia and Antarctica formed which disrupted ocean currents worldwide and as a result causes a global cooling effect, shrinking the jungles. This allowed mammals to grow to mammoth proportions, such as whales which are, by now, fully aquatic. Mammals like Andrewsarchus were now at the top of the food-chain. The Late-Eocene saw the rebirth of seasons, which caused the expansion of savanna-like areas, along with the evolution of grass.
The Oligocene Epoch spans from 33 million to 23 million years ago. The expansion of grass led to many new species to evolve, including the first elephants, cats, dogs, marsupials and many other species still prevalent today. Many other species of plants evolved in this period to, such as the evergreen trees. A cooling period was still in effect and seasonal rains were as well. Mammals still continued to grow larger and larger. Paraceratherium, the largest land mammal to ever live evolved during this period, along with many other perissodactyls in an event known as the Grand coupre.
The Miocene spans from 23 to 5 million years ago and is a period in which grass spreads further across, effectively dominating a large portion of the world, diminishing forests in the process. Kelp forests evolved, leading to new species such as sea otters to evolve. During this time, perissodactyls thrived, and evolved into many different varieties. Alongside them were the apes, which evolved into a staggering 30 species. Overall, arid and mountainous land dominated most of the world, as did grazers. The Tethys Sea finally closed with the creation of the Arabian Peninsula and in its wake left the Black, Red, Mediterranean and Caspian Seas. This only increased aridity. Many new plants evolved, and 95% of modern seed plants evolved in the mid-Miocene.
The Pliocene ranges from 5 to 2 million years ago. The Pliocene features dramatic climactic changes, which ultimately leads to modern species and plants. The most dramatic are the formation of Panama, and the accumulation of ice at the poles, leading to a massive die-off, India and Asia collide forming the Himalayas, the Rockies and Appalachian mountain ranges were formed, and the Mediterranean Sea dried up for the next several million years. Along with these major geological events, the Australopithecus evolves in Africa, beginning the human branch. Also, with the isthmus of Panama, animals migrate across North and South America, wreaking havoc on the local ecology. Climactic changes bring along savannas that are still continuing to spread across the world, Indian monsoons, deserts in East Asia, and the beginnings of the Sahara desert. The earth's continents and seas move into their present shapes, and the world map hasn't changed much since. 
The Quaternary ranges from 3 million to present day, and features modern animals, and dramatic climate changes and features two epochs: the Pleistocene and the Holocene.
The Pleistocene lasted from 3 million to 12,000 years ago. This epoch features the ice ages which is a result from the cooling effect that started in the Mid-Eocene. As the ice progressively migrated towards the equator, the areas north and south of the tropic line featured intense winters yet mild summers. Meanwhile, Africa experienced terrible droughts which resulted in the creation of the Sahara, Namib, and Kalahari deserts. To cope, many animals evolved including Mammoths, Giant ground sloths, Dire wolves and most famously Homo sapiens. 100,000 years ago marked the end of one of he worst droughts of Africa, and the expansion of primitive man. As the Pleistocene draws to a close, one of the largest die-outs causes many mega-fauna to die off, including the last hominid species (excluding Homo sapiens). All continents are effected, but Africa isn't hit quite as hard.
The Holocene ranges from 12,000 years ago to present day. Also known as "the Age of Man", the Holocene features the rise of man on his path to sentience. All recorded history lies within the boundaries of the Holocene epoch. Human activity, however are being blamed for a die-out that has been going on since 10,000 B.C.E. commonly referred to as "the Sixth Extinction" with an estimated extinction rate of 140,000 species per year. The most famous extinct species include: the Quagga, the Aurochs, the Passenger Pigeon, and the Moa.
Geologically, the Cenozoic is the era when the continents moved into their current positions. Australia-New Guinea, having split from Pangea during the early Cretaceous, drifted north and, eventually, collided with South-east Asia; Antarctica moved into its current position over the South Pole; the Atlantic Ocean widened and, later in the era, South America became attached to North America with the isthmus of Panama.
The Paleocene–Eocene Thermal Maximum of was a significant global warming event; however, since the Azolla event of , the Cenozoic Era has been a period of long-term cooling. After the tectonic creation of Drake Passage, when South America fully detached from Antarctica during the Oligocene, the climate cooled significantly due to the advent of the Antarctic Circumpolar Current which brought cool deep Antarctic water to the surface. The cooling trend continued in the Miocene, with relatively short warmer periods. When South America became attached to North America creating the Isthmus of Panama, the Arctic region cooled due to the strengthening of the Humboldt and Gulf Stream currents, eventually leading to the glaciations of the Quaternary ice age, the current interglacial of which is the Holocene Epoch.
During the Cenozoic, mammals proliferated from a few small, simple, generalized forms into a diverse collection of terrestrial, marine, and flying animals, giving this period its other name, the Age of Mammals, despite the fact that birds still outnumbered mammals two to one. The Cenozoic is just as much the age of savannas, the age of co-dependent flowering plants and insects, and the age of birds. Grass also played a very important role in this era, shaping the evolution of the birds and mammals that fed on it. One group that diversified significantly in the Cenozoic as well were the snakes. 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.
In the earlier part of the Cenozoic, the world was dominated by the gastornid birds, terrestrial crocodiles like Pristichampsus, and a handful of primitive large mammal groups like uintatheres, mesonychids, and pantodonts. But as the forests began to recede and the climate began to cool, other mammals took over.
The Cenozoic is full of mammals both strange and familiar, including chalicotheres, creodonts, whales, primates, entelodonts, saber-toothed cats, mastodons and mammoths, three-toed horses, giant rhinoceros like Indricotherium, 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.
|Wikisource has the text of the 1911 Encyclopædia Britannica article Cainozoic.|
|Wikimedia Commons has media related to Cenozoic.|
- Cretaceous–Paleogene boundary (K–T boundary)
- Geologic time scale
- Phanerozoic Eon
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- International Stratigraphic Chart
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|Preceded by Proterozoic Eon||Phanerozoic Eon|
|Paleozoic Era||Mesozoic Era||Cenozoic Era|