The Cenozoic ( ; ) is Earth's current geological

era An era is a span of time defined for the purposes of chronology or historiography, as in the regnal eras in the history of a given monarchy, a calendar era used for a given calendar, or the geological eras defined for the history of Earth. Compa ...

, representing the last 66million years of Earth's history. It is characterised by the dominance of

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

s, birds and flowering plants, a cooling and drying climate, and the current configuration of continents. It is the latest of three geological eras since complex life evolved, preceded by the Mesozoic and Paleozoic. It started with the Cretaceous–Paleogene extinction event, when many species, including the non-avian

dinosaurs Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

, became extinct in an event attributed by most experts to the impact of a large asteroid or other celestial body, the Chicxulub impactor. The Cenozoic is also known as the Age of Mammals because the terrestrial animals that dominated both hemispheres were

sthe eutherians (placentals) in the northern hemisphere and the metatherians (marsupials, now mainly restricted to Australia) in the southern hemisphere. The extinction of many groups allowed mammals and birds to greatly diversify so that large mammals and birds dominated life on Earth. The continents also moved into their current positions during this era. The climate during the early Cenozoic was warmer than today, particularly during the

Paleocene–Eocene Thermal Maximum The Paleocene–Eocene thermal maximum (PETM), alternatively (ETM1), and formerly known as the "Initial Eocene" or "", was a time period with a more than 5–8 °C global average temperature rise across the event. This climate event o ...

. However, the Eocene to

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

transition and the Quaternary glaciation dried and cooled Earth.

Nomenclature

''Cenozoic'' derives from the Greek words ( 'new') and ( 'life'). The name was proposed in 1840 by the British geologist John Phillips (1800–1874), who originally spelled it ''Kainozoic''. The era is also known as the ''Cænozoic'', ''Caenozoic'', or ''Cainozoic'' (). In name, the Cenozoic () is comparable to the preceding Mesozoic ('middle life') and Paleozoic ('old life') Eras, as well as to the Proterozoic ('earlier life') Eon.

Divisions

The Cenozoic is divided into three periods: the

Paleogene The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...

Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...

, and

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

; and seven epochs: the Paleocene, Eocene,

, Miocene, Pliocene, Pleistocene, and Holocene. The Quaternary Period was officially recognised by the International Commission on Stratigraphy in June 2009. In 2004, the Tertiary Period was officially replaced by the Paleogene and Neogene Periods. 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. Knowledge of this era is more detailed than any other era because of the relatively young, well-preserved rocks associated with it.

Paleogene

The Paleogene spans from the extinction of non-avian dinosaurs, 66 million years ago, to the dawn of the Neogene, 23.03 million years ago. It features three epochs: the Paleocene, Eocene and

The

Paleocene Epoch The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''palaiós ...

lasted from 66 million to 56 million years ago. Modern placental mammals originated during this time. The devastation of the K–Pg extinction event included the extinction of large herbivores, which permitted the spread of dense but usually species-poor forests. The Early Paleocene saw the recovery of Earth. The continents began to take their modern shape, but all the continents and the subcontinent of India were separated from each other.

Afro-Eurasia Afro-Eurasia (also Afroeurasia, Eurafrasia or the Old World) is a landmass comprising the continents of Africa, Asia, and Europe. The terms are compound words of the names of its constituent parts. Its mainland is the largest and most populou ...

was separated by the Tethys Sea, and the Americas were separated by the strait of Panama, as the isthmus had not yet formed. This epoch featured a general warming trend, with jungles eventually reaching the poles. The oceans were dominated by sharks as the large reptiles that had once predominated were extinct. Archaic mammals filled the world such as creodonts (extinct carnivores, unrelated to existing

Carnivora Carnivora is a Clade, monophyletic order of Placentalia, placental mammals consisting of the most recent common ancestor of all felidae, cat-like and canidae, dog-like animals, and all descendants of that ancestor. Members of this group are f ...

). The Eocene Epoch ranged from 56 million years to 33.9 million years ago. In the Early-Eocene, species living in dense forest were unable to evolve into larger forms, as in the Paleocene. All known mammals were under 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 Paracrax. The temperature was 30 degrees Celsius with little temperature gradient from pole to pole. In the Mid-Eocene, the Circumpolar-Antarctic current between Australia and Antarctica formed. This disrupted ocean currents worldwide and as a result caused a global cooling effect, shrinking the jungles. This allowed mammals to grow to mammoth proportions, such as whales which, by that time, had become almost fully aquatic. Mammals like ''

Andrewsarchus ''Andrewsarchus'' () is an extinct genus of mammal that lived during the middle Eocene epoch in what is now Inner Mongolia, China. Only one species is usually recognized, ''A. mongoliensis'', known from a single skull of great size discovered in ...

'' were 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 grasses. The end of the Eocene was marked by the Eocene-Oligocene extinction event, the European face of which is known as the

Grande Coupure Grande means "large" or "great" in many of the Romance languages. It may also refer to: Places * Grande, Germany, a municipality in Germany *Grande Communications, a telecommunications firm based in Texas *Grande-Rivière (disambiguation) *Arroi ...

. The

Oligocene Epoch The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but th ...

spans from 33.9 million to 23.03 million years ago. The Oligocene featured the expansion of grasslands which had 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 too. A cooling period featuring seasonal rains was still in effect. Mammals still continued to grow larger and larger.

Neogene

The Neogene spans from 23.03 million to 2.58 million years ago. It features 2 epochs: the Miocene, and the Pliocene. 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. Kelp forests evolved, encouraging the evolution of new species, such as

sea otter The sea otter (''Enhydra lutris'') is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adult sea otters typically weigh between , making them the heaviest members of the weasel family, but among the small ...

s. During this time, perissodactyla thrived, and evolved into many different varieties.

Apes Apes (collectively Hominoidea ) are a clade of Old World simians native to sub-Saharan Africa and Southeast Asia (though they were more widespread in Africa, most of Asia, and as well as Europe in prehistory), which together with its sister g ...

evolved into 30 species. The Tethys Sea finally closed with the creation of the

Arabian Peninsula The Arabian Peninsula, (; ar, شِبْهُ الْجَزِيرَةِ الْعَرَبِيَّة, , "Arabian Peninsula" or , , "Island of the Arabs") or Arabia, is a peninsula of Western Asia, situated northeast of Africa on the Arabian Plate ...

, leaving only remnants as the Black, Red, Mediterranean and Caspian Seas. This increased aridity. Many new plants evolved: 95% of modern seed plants evolved in the mid-Miocene. The

Pliocene Epoch The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58ice ages reduced sea levels, disconnecting the Atlantic from the Mediterranean, and evaporation rates exceeded inflow from rivers). '' Australopithecus'' evolved in Africa, beginning the human branch. The

isthmus of Panama The Isthmus of Panama ( es, Istmo de Panamá), also historically known as the Isthmus of Darien (), is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North and South America. It contains the country ...

formed, and animals migrated between North and South America during the

great American interchange The Great American Biotic Interchange (commonly abbreviated as GABI), also known as the Great American Interchange and the Great American Faunal Interchange, was an important late Cenozoic paleozoogeographic biotic interchange event in which lan ...

, wreaking havoc on local ecologies. Climatic changes brought: savannas that are still continuing to spread across the world; Indian monsoons;

desert A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About on ...

s in central Asia; and the beginnings of the

Sahara , photo = Sahara real color.jpg , photo_caption = The Sahara taken by Apollo 17 astronauts, 1972 , map = , map_image = , location = , country = , country1 = , ...

desert. The world map has not changed much since, save for changes brought about by the

glaciations A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betwe ...

of the Quaternary, such as the Great Lakes,

Hudson Bay Hudson Bay ( crj, text=ᐐᓂᐯᒄ, translit=Wînipekw; crl, text=ᐐᓂᐹᒄ, translit=Wînipâkw; iu, text=ᑲᖏᖅᓱᐊᓗᒃ ᐃᓗᐊ, translit=Kangiqsualuk ilua or iu, text=ᑕᓯᐅᔭᕐᔪᐊᖅ, translit=Tasiujarjuaq; french: b ...

, and the Baltic sea.

Quaternary

The

spans from 2.58 million years ago to present day, and is the shortest geological period in the Phanerozoic Eon. It features modern animals, and dramatic changes in the climate. It is divided into two epochs: the Pleistocene and the Holocene. Ice age fauna of northern Spain - Mauricio Antón

Ice age fauna of northern Spain - Mauricio Antón

The Pleistocene lasted from 2.58 million to 11,700 years ago. This epoch was marked by ice ages as a result of the cooling trend that started in the Mid-Eocene. There were at least four separate glaciation periods marked by the advance of ice caps as far south as 40° N in mountainous areas. Meanwhile, Africa experienced a trend of

desiccation Desiccation () is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its local vicinity in a moderately sealed container. ...

which resulted in the creation of the

Sahara , photo = Sahara real color.jpg , photo_caption = The Sahara taken by Apollo 17 astronauts, 1972 , map = , map_image = , location = , country = , country1 = , ...

, Namib, and Kalahari deserts. Many animals evolved including mammoths,

giant ground sloths ''Megatherium'' ( ; from Greek () 'great' + () 'beast') is an extinct genus of ground sloths endemic to South America that lived from the Early Pliocene through the end of the Pleistocene. It is best known for the elephant-sized type species ' ...

dire wolves The dire wolf (''Aenocyon dirus'' ) is an extinct canine. It is one of the most famous prehistoric carnivores in North America, along with its extinct competitor ''Smilodon''. The dire wolf lived in the Americas and eastern Asia during the L ...

, sabre-toothed cats, and most famously '' 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. All the continents were affected, but Africa to a lesser extent. It still retains many large animals, such as hippos. The Holocene began 11,700 years ago and lasts to the present day. All recorded history and "the

Human history Human history, also called world history, is the narrative of humanity's past. It is understood and studied through anthropology, archaeology, genetics, and linguistics. Since the invention of writing, human history has been studied throug ...

" lies within the boundaries of the Holocene Epoch. Human activity is blamed for a mass extinction that began roughly 10,000 years ago, though the species becoming extinct have only been recorded since the Industrial Revolution. This is sometimes referred to as the " Sixth Extinction". It is often cited that over 322 recorded species have become extinct due to human activity since the Industrial Revolution, but the rate may be as high as 500 vertebrate species alone, the majority of which have occurred after 1900.

Tectonics

Geologically, the Cenozoic is the era when the continents moved into their current positions.

Australia-New Guinea The continent of Australia, sometimes known in technical contexts by the names Sahul (), Australia-New Guinea, Australinea, Meganesia, or Papualand to distinguish it from the country of Australia, is located within the Southern and East ...

, 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 (2.8 million years ago), South America became attached to

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

with the

. India collided with Asia creating the Himalayas; Arabia collided with Eurasia, closing the Tethys Ocean and creating the Zagros Mountains, around . The break-up of Gondwana in Late Cretaceous and Cenozoic times led to a shift in the river courses of various large African rivers including the

Congo Congo or The Congo may refer to either of two countries that border the Congo River in central Africa: * Democratic Republic of the Congo, the larger country to the southeast, capital Kinshasa, formerly known as Zaire, sometimes referred to a ...

, Niger, Nile, Orange, Limpopo and Zambezi.

Climate

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. This continued for the first 10 million years of the Paleocene, culminating in the

about . Around Earth entered a period of long term cooling. This was mainly due to the collision of India with Eurasia, which caused the rise of the Himalayas: the upraised rocks eroded and reacted with in the air, causing a long-term reduction in the proportion of this greenhouse gas in the atmosphere. Around permanent ice began to build up on Antarctica. 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 Isthmus of Panama ( es, Istmo de Panamá), also historically known as the Isthmus of Darien (), is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North and South America. It contains the country ...

around , the Arctic region cooled due to the strengthening of the Humboldt and

Gulf Stream The Gulf Stream, together with its northern extension the North Atlantic Current, North Atlantic Drift, is a warm and swift Atlantic Ocean, Atlantic ocean current that originates in the Gulf of Mexico and flows through the Straits of Florida a ...

currents, eventually leading to the glaciations of the

Quaternary ice age The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

, the current

interglacial An interglacial period (or alternatively interglacial, interglaciation) is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene in ...

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.

Life

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 dinosaurs that had dominated during the Mesozoic. Some flightless birds grew larger than humans. These species are sometimes referred to as "

terror bird Phorusrhacids, colloquially known as terror birds, are an extinct clade of large carnivorous flightless birds that were one of the largest species of apex predators in South America during the Cenozoic era; their conventionally accepted temporal ...

s", and were formidable predators. Mammals came to occupy almost every available

niche Niche may refer to: Science *Developmental niche, a concept for understanding the cultural context of child development *Ecological niche, a term describing the relational position of an organism's species *Niche differentiation, in ecology, the ...

(both marine and terrestrial), and some also grew very large, attaining sizes not seen in most of today's terrestrial mammals. During the Cenozoic, mammals proliferated from a few small, simple, generalised forms into a diverse collection of terrestrial,

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

, and

flying Flying may refer to: * Flight, the process of flying * Aviation, the creation and operation of aircraft Music Albums * ''Flying'' (Grammatrain album), 1997 * ''Flying'' (Jonathan Fagerlund album), 2008 * ''Flying'' (UFO album), 1971 * ''Fl ...

animals, giving this period its other name, the Age of Mammals. The Cenozoic is just as much the age of savannas, the age of co-dependent flowering plants and insects, and the age of birds. Grasses also played a very important role in this era, shaping the evolution of the birds and mammals that fed on them. 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 gastornithid birds, terrestrial

crocodile Crocodiles (family (biology), family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to inclu ...

s like ''

Pristichampsus ''Pristichampsus'' ("saw crocodile") is a non-diagnostic extinct genus of crocodylian from France and possibly also Kazakhstan that is part of the monotypic Pristichampsidae family. As the type species, ''Pristichampsus rollinatii'', was based o ...

'', and a handful of primitive large mammal groups like

uintathere Uintatheriidae is a family of extinct ungulate mammals that includes ''Uintatherium''. Uintatheres belong to the order Dinocerata, one of several extinct orders of primitive hoofed mammals that are sometimes united in the Condylarthra. Uintathe ...

s, 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

chalicothere Chalicotheres (from Greek '' chalix'', "gravel" and '' therion'', "beast") are an extinct clade of herbivorous, odd-toed ungulate (perissodactyl) mammals that lived in North America, Eurasia, and Africa from the Middle Eocene until the Early Plei ...

s, creodonts, whales, primates, entelodonts,

sabre-toothed cat Machairodontinae is an extinct subfamily of carnivoran mammals of the family Felidae (true cats). They were found in Asia, Africa, North America, South America, and Europe from the Miocene to the Pleistocene, living from about 16 million until ...

s, mastodons and mammoths,

three-toed horse ''Miohippus'' (meaning "small horse") was a genus of prehistoric horse existing longer than most Equidae. ''Miohippus'' lived in what is now North America from 32 to 25 million years ago, during the late Eocene to late Oligocene. ''Miohippus'' ...

s, giant rhinoceros like '' Paraceratherium'', the rhinoceros-like brontotheres, various bizarre groups of mammals from South America, such as the vaguely elephant-like

pyrothere Pyrotheria is an order of extinct meridiungulate mammals. These mastodon-like ungulates include the genera ''Baguatherium'', ''Carolozittelia'', ''Colombitherium'', ''Griphodon'', ''Propyrotherium'', ''Proticia'', and ''Pyrotherium''. They had ...

s and the dog-like marsupial relatives called

borhyaenids Borhyaenidae is an extinct metatherian family (biology), family of low-slung, heavily built predatory mammals in the order Sparassodonta. Borhyaenids are not true marsupials, but members of a sister taxon, Sparassodonta. Like most metatherians, ...

and the

monotreme Monotremes () are prototherian mammals of the order Monotremata. They are one of the three groups of living mammals, along with placentals (Eutheria), and marsupials (Metatheria). Monotremes are typified by structural differences in their brain ...

s and marsupials of Australia.

References

External links

Western Australian Museum – The Age of the Mammals

{{Authority control Geological eras