The Cenozoic is also known as theAge of Mammals because the terrestrial animals that dominated both hemispheres were mammals – theeutherians (placentals) in the Northern Hemisphere and themetatherians (marsupials, now mainly restricted toAustralia and to some extentSouth America) 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.
Cenozoic derives from theAncient Greek wordskainós (καινός, 'new') andzōḗ (ζωή, 'life').[4] The name was proposed in 1840 by the British geologistJohn Phillips (1800–1874), who originally spelled itKainozoic.[5][6][7] The era is also known as theCænozoic,Caenozoic, orCainozoic (/ˌkaɪ.nəˈzoʊ.ɪk,ˌkeɪ-/).[8][9]
The Cenozoic is divided into three periods: thePaleogene,Neogene, andQuaternary; and sevenepochs: thePaleocene,Eocene,Oligocene,Miocene,Pliocene,Pleistocene, andHolocene. The Quaternary Period was officially recognised by theInternational Commission on Stratigraphy in June 2009.[10] In 2004, theTertiary Period was officially replaced by the Paleogene and Neogene Periods. The common use of epochs during the Cenozoic helpspalaeontologists 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.
ThePaleogene 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 threeepochs: thePaleocene,Eocene andOligocene.
ThePaleocene Epoch lasted from 66 million to 56 million years ago. Modern placental mammals originated during this time.[11] The devastation of theK–Pg extinction event included the extinction of largeherbivores, which permitted the spread of dense but usually species-poor forests.[12][13] 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 was separated by theTethys Sea, and the Americas were separated by the strait of Panama, as theisthmus had not yet formed. This epoch featured a general warming trend, with jungles eventually reaching the poles. The oceans were dominated by sharks[14] as the large reptiles that had once predominated were extinct. Archaic mammals filled the world such ascreodonts (extinct carnivores, unrelated to existingCarnivora).
TheEocene 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. 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 asParacrax. Carbon dioxide levels were approximately 1,400ppm.[15] The temperature was 30 degrees Celsius with little temperature gradient from pole to pole. In the Mid-Eocene, theAntarctic Circumpolar 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 likeAndrewsarchus 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 ofgrasses.[16][17] The end of the Eocene was marked by theEocene–Oligocene extinction event,[18][19][20] the European face of which is known as theGrande Coupure.[21][22]
TheOligocene 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.[23]
TheNeogene spans from 23.03 million to 2.58 million years ago. It features two epochs: the Miocene, and the Pliocene.[24]
TheMiocene Epoch spans from 23.03 to 5.333 million years ago and is a period in whichgrasses spread further, dominating a large portion of the world, at the expense of forests.Kelp forests evolved, encouraging the evolution of new species, such assea otters. During this time,Perissodactyla thrived, and evolved into many different varieties.Apes evolved into 30 species. TheTethys Sea finally closed with the creation of theArabian Peninsula, leaving only remnants as theBlack,Red,Mediterranean andCaspian Seas. This increased aridity. Many new plants evolved: 95% of modernseed plants families were present by the end of the Miocene.[25]
ThePliocene Epoch lasted from 5.333 to 2.58 million years ago. The Pliocene featured dramatic climatic changes, which ultimately led to modern species of flora and fauna. The Mediterranean Sea dried up for several million years (because theice ages reduced sea levels, disconnecting theAtlantic from the Mediterranean, and evaporation rates exceeded inflow from rivers).Australopithecus evolved inAfrica, beginning the human branch. TheIsthmus of Panama formed, and animals migrated betweenNorth andSouth America during thegreat American interchange, wreaking havoc on local ecologies. Climatic changes brought:savannas that are still continuing to spread across the world; Indianmonsoons;deserts in centralAsia; and the beginnings of theSahara desert. The world map has not changed much since, save for changes brought about by theglaciations of the Quaternary, such as theGreat Lakes,Hudson Bay, and theBaltic Sea.[26][27]
TheQuaternary spans from 2.58 million years ago to present day, and is the shortest geological period in thePhanerozoic Eon. It features modern animals, and dramatic changes in the climate. It is divided into two epochs: the Pleistocene and the Holocene.
ThePleistocene lasted from 2.58 million to 11,700 years ago. This epoch was marked byice 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 ofdesiccation which resulted in the creation of theSahara,Namib, andKalahari deserts. Many animals evolved includingmammoths,giant ground sloths,dire wolves, sabre-toothed cats, andHomo 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 asNeanderthals. All the continents were affected, but Africa to a lesser extent. It still retains many large animals, such as hippos.[28]
TheHolocene began 11,700 years ago and lasts to the present day. All recorded history and "theHuman history" lies within the boundaries of the Holocene Epoch.[29] 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 theIndustrial 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,[30][31] but the rate may be as high as 500 vertebrate species alone, the majority of which have occurred after 1900.[32]
India collided with Asia55 to 45 million years ago creating the Himalayas; Arabia collided with Eurasia, closing theTethys Ocean and creating theZagros Mountains, around35 million years ago.[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. This continued for the first 10 million years of the Paleocene, culminating in thePaleocene–Eocene Thermal Maximum about55.5 million years ago. Around50 million years ago, Earth entered a period of long term cooling. This was mainly due to the collision of India with Eurasia, which caused the rise of theHimalayas: the upraised rocks eroded and reacted with CO2 in the air, causing a long-term reduction in the proportion of this greenhouse gas in the atmosphere. Around35 million years ago, permanent ice began to build up on Antarctica.[35] The cooling trend continued in theMiocene, with relatively short warmer periods. When South America became attached to North America creating theIsthmus of Panama around2.8 million years ago, the Arctic region cooled due to the strengthening of theHumboldt andGulf Stream currents,[36] eventually leading to the glaciations of theQuaternary ice age, the currentinterglacial of which is theHolocene 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.[37] The levels of carbonate ions in the ocean fell over the course of the Cenozoic.[38]
Restoration ofPalaeotherium, aPaleogene relative of horses that lived in subtropical climates of Europe during theEocene
Early in the Cenozoic, following theK-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 to greatly diversify in the absence of the dinosaurs that had dominated during the Mesozoic.[39] Birds also diversified rapidly; some flightless birds grew larger than humans. These species are sometimes referred to as "terror birds", and were formidable predators. Mammals came to occupy almost every availableniche (both marine andterrestrial), and some also grew very large, attaining sizes not seen in most of today's terrestrial mammals. 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]
During the Cenozoic,mammals proliferated from a few small, simple, generalised forms into a diverse collection ofterrestrial,marine, andflying animals, giving this period its other name, the Age of Mammals. The Cenozoic is just as much the age ofsavannas, the age of co-dependentflowering plants andinsects, and the age of birds.[41]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 thesnakes. Evolving in the Cenozoic, the variety of snakes increased tremendously, resulting in manycolubrids, following the evolution of their current primary prey source, therodents.
In the earlier part of the Cenozoic, the world was dominated by thegastornithid birds, terrestrialcrocodylians likePristichampsus, large sharks such asOtodus, and a handful of primitive large mammal groups likeuintatheres,mesonychians, andpantodonts. But as the forests began to recede and the climate began to cool, other mammals took over.
Cenozoiccalcareous 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.[44] Diatom diversification was particularly concentrated at the Eocene-Oligocene boundary. A second major pulse of diatom diversification occurred over the course of the Middle and Late Miocene.[45]
^Gallipoli (Map) (2nd ed.). 1:100,000. Carta Geologica d'Italia (Scala 1:100.000). Dipartimento per il Servizio Geologico d'Italia. 1968. Sheet :Foglio 214. Retrieved31 May 2025.
^Phillips, John (1840)."Palæozoic series".Penny Cyclopaedia of the Society for the Diffusion of Useful Knowledge. Vol. 17. London, England: Charles Knight and Co. pp. 153–154. From pp. 153–154: "As many systems or combinations of organic forms as are clearly traceable in the stratified crust of the globe, so many corresponding terms (as Palæozoic, Mesozoic, Kainozoic, &c.) may be made, ... "
^The evolution of the spelling of "Cenozoic" is reviewed in:
Harland, W. Brian; Armstrong, Richard L.; Cox, Allen V.; Craig, Lorraine E.; Smith, David G.; Smith, Alan G. (1990)."The Chronostratic Scale".A Geologic Time Scale 1989. Cambridge, England, U.K.: Cambridge University Press. p. 31.ISBN978-0-521-38765-1.
Although John Phillips originally spelled it as "Kainozoic" in 1840, he spelled it "Cainozoic" a year later:
^O'Leary, Maureen A.; Bloch, Jonathan I.; Flynn, John J.; Gaudin, Timothy J.; Giallombardo, Andres; Giannini, Norberto P.; Goldberg, Suzann L.; Kraatz, Brian P.; Luo, Zhe-Xi; Meng, Jin; Ni, Michael J.; Novacek, Fernando A.; Perini, Zachary S.; Randall, Guillermo; Rougier, Eric J.; Sargis, Mary T.; Silcox, Nancy b.; Simmons, Micelle; Spaulding, Paul M.; Velazco, Marcelo; Weksler, John r.; Wible, Andrea L.; Cirranello, A. L. (8 February 2013). "The Placental Mammal Ancestor and the Post–K-Pg Radiation of Placentals".Science.339 (6120):662–667.Bibcode:2013Sci...339..662O.doi:10.1126/science.1229237.hdl:11336/7302.PMID23393258.S2CID206544776.
^Williams, C. J.; LePage, B. A.; Johnson, A. H.; Vann, D. R. (2009). "Structure, Biomass, and Productivity of a Late Paleocene Arctic Forest".Proceedings of the Academy of Natural Sciences of Philadelphia.158 (1):107–127.Bibcode:2009PANSP.158..107W.doi:10.1635/053.158.0106.S2CID130110536.
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