Temporal range: Late Triassic–Recent; 225 or 167–0 Ma See discussion of dates in text
Common vampire batTasmanian devilFox squirrelPlatypusHumpback whaleGiant armadilloVirginia opossumHumanTree pangolinColugoStar nosed molePlains zebraEastern grey kangarooNorthern elephant sealAfrican elephantReindeerGiant pandaBlack and rufous elephant shrewMammal Diversity 2011.png
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Scientific classification edit
Linnaeus, 1758
Living subgroups

Mammals are the vertebrates within the class Mammalia (ə/ from Latin mamma "breast"), a clade of endothermic amniotes distinguished from reptiles (including birds) by the possession of a neocortex (a region of the brain), hair, three middle ear bones, and mammary glands. Females of all mammal species nurse their young with milk, secreted from the mammary glands.

Mammals include the largest animal on the planet, the blue whale. The basic body type is a terrestrial quadruped, but some mammals are adapted for life at sea, in the air, in trees, underground or on two legs. The largest group of mammals, the placentals, have a placenta, which enables the feeding of the fetus during gestation.Mammals range in size from the 30–40 mm (1.2–1.6 in) bumblebee bat to the 30-meter (98 ft) blue whale. With the exception of the five species of monotreme (egg-laying mammals), all modern mammals give birth to live young. Most mammals, including the six most species-rich orders, belong to the placental group. The largest orders are the rodents, bats and Soricomorpha (shrews and allies). The next three biggest orders, depending on the biological classification scheme used, are the Primates (apes, monkeys, and allies), the Cetartiodactyla (whales and even-toed ungulates), and the Carnivora (cats, dogs, seals, and allies).

Living mammals are divided into the Yinotheria (platypus and echidnas) and Theriiformes (all other mammals). There are around 5,450 species of mammal, depending on which authority is cited. In some classifications, extant mammals are divided into two subclasses: the Prototheria, that is, the order Monotremata; and the Theria, or the infraclasses Metatheria and Eutheria. The marsupials constitute the crown group of the Metatheria, and include all living metatherians as well as many extinct ones; the placentals are the crown group of the Eutheria. While mammal classification at the family level has been relatively stable, several contending classifications regarding the higher levels—subclass, infraclass and order, especially of the marsupials—appear in contemporaneous literature. Much of the changes reflect the advances of cladistic analysis and molecular genetics. Findings from molecular genetics, for example, have prompted adopting new groups, such as the Afrotheria, and abandoning traditional groups, such as the Insectivora.

The mammals represent the only living Synapsida, which together with the Sauropsida form the Amniota clade. The early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period, this group diverged from the sauropsid line that led to today's reptiles and birds. The line following the stem group Sphenacodontia split-off several diverse groups of non-mammalian synapsids—sometimes referred to as mammal-like reptiles—before giving rise to the proto-mammals (Therapsida) in the early Mesozoic era. The modern mammalian orders arose in the Paleogene and Neogene periods of the Cenozoic era, after the extinction of non-avian dinosaurs, and have been among the dominant terrestrial animal groups from 66 million years ago to the present.

Most mammals are intelligent, with some possessing large brains, self-awareness and tool use. Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals, singing, and echolocation. Mammals can organize themselves into fission-fusion societies, harems, and hierarchies, but can also be solitary and territorial. Most mammals are polygynous, but some can be monogamous or polyandrous.

In human culture, domesticated mammals played a major role in the Neolithic revolution, causing farming to replace hunting and gathering, and leading to a major restructuring of human societies with the first civilizations. They provided, and continue to provide, power for transport and agriculture, as well as various commodities such as meat, dairy products, wool, and leather. Mammals are hunted or raced for sport, and are used as model organisms in science. Mammals have been depicted in art since Palaeolithic times, and appear in literature, film, mythology, and religion. Defaunation of mammals is primarily driven by anthropogenic factors, such as poaching and habitat destruction, though there are efforts to combat this.


The orders Rodentia (blue), Chiroptera (red) and Soricomorpha (yellow) together make up over 70% of mammal species.

Mammal classification has been through several iterations since Carl Linnaeus initially defined the class. No classification system is universally accepted; McKenna & Bell (1997) and Wilson & Reader (2005) provide useful recent compendiums.[1] George Gaylord Simpson's "Principles of Classification and a Classification of Mammals" (AMNH Bulletin v. 85, 1945) provides systematics of mammal origins and relationships that were universally taught until the end of the 20th century. Since Simpson's classification, the paleontological record has been recalibrated, and the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself, partly through the new concept of cladistics. Though field work gradually made Simpson's classification outdated, it remains the closest thing to an official classification of mammals.[2]

Most mammals, including the six most species-rich orders, belong to the placental group. The three largest orders in numbers of species are Rodentia: mice, rats, porcupines, beavers, capybaras and other gnawing mammals; Chiroptera: bats; and Soricomorpha: shrews, moles and solenodons. The next three biggest orders, depending on the biological classification scheme used, are the Primates including the apes, monkeys and lemurs; the Cetartiodactyla including whales and even-toed ungulates; and the Carnivora which includes cats, dogs, weasels, bears, seals and allies.[3] According to Mammal Species of the World, 5,416 species were identified in 2006. These were grouped into 1,229 genera, 153 families and 29 orders.[3] In 2008, the International Union for Conservation of Nature (IUCN) completed a five-year Global Mammal Assessment for its IUCN Red List, which counted 5,488 species.[4] According to a research published in the Journal of Mammalogy in 2018, the number of recognized mammal species is 6,495 species included 96 recently extinct.[5]


The word "mammal" is modern, from the scientific name Mammalia coined by Carl Linnaeus in 1758, derived from the Latin mamma ("teat, pap"). In an influential 1988 paper, Timothy Rowe defined Mammalia phylogenetically as the crown group of mammals, the clade consisting of the most recent common ancestor of living monotremes (echidnas and platypuses) and therian mammals (marsupials and placentals) and all descendants of that ancestor.[6] Since this ancestor lived in the Jurassic period, Rowe's definition excludes all animals from the earlier Triassic, despite the fact that Triassic fossils in the Haramiyida have been referred to the Mammalia since the mid-19th century.[7] If Mammalia is considered as the crown group, its origin can be roughly dated as the first known appearance of animals more closely related to some extant mammals than to others. Ambondro is more closely related to monotremes than to therian mammals while Amphilestes and 167 million years ago in the Middle Jurassic, this is a reasonable estimate for the appearance of the crown group.[8]

T. S. Kemp has provided a more traditional definition: "synapsids that possess a dentarysquamosal jaw articulation and occlusion between upper and lower molars with a transverse component to the movement" or, equivalently in Kemp's view, the clade originating with the last common ancestor of Sinoconodon and living mammals.[9] The earliest known synapsid satisfying Kemp's definitions is 225 Ma, so the appearance of mammals in this broader sense can be given this Late Triassic date.[10][11]

McKenna/Bell classification

In 1997, the mammals were comprehensively revised by Malcolm C. McKenna and Susan K. Bell, which has resulted in the McKenna/Bell classification. Their 1997 book, Classification of Mammals above the Species Level,[12] is a comprehensive work on the systematics, relationships and occurrences of all mammal taxa, living and extinct, down through the rank of genus, though molecular genetic data challenge several of the higher level groupings. The authors worked together as paleontologists at the American Museum of Natural History, New York. McKenna inherited the project from Simpson and, with Bell, constructed a completely updated hierarchical system, covering living and extinct taxa that reflects the historical genealogy of Mammalia.[2]

Extinct groups are represented by a dagger (†).

Class Mammalia

Molecular classification of placentals

Molecular studies based on DNA analysis have suggested new relationships among mammal families over the last few years. Most of these findings have been independently validated by retrotransposon presence/absence data.[14] Classification systems based on molecular studies reveal three major groups or lineages of placental mammals—Afrotheria, Xenarthra and Boreoeutheria—which diverged in the Cretaceous. The relationships between these three lineages is contentious, and all three possible different hypotheses have been proposed with respect to which group is basal. These hypotheses are Atlantogenata (basal Boreoeutheria), Epitheria (basal Xenarthra) and Exafroplacentalia (basal Afrotheria).[15] Boreoeutheria in turn contains two major lineages—Euarchontoglires and Laurasiatheria.

Estimates for the divergence times between these three placental groups range from 105 to 120 million years ago, depending on the type of DNA used (such as nuclear or mitochondrial)[16] and varying interpretations of paleogeographic data.[15]


Monotremata Ornithorhynchus anatinus


Marsupialia Macropodidæ


Afrotheria Elephas maximus Trichechus

Xenarthra Dasypus novemcinctus Myrmecophaga tridactyla


Euarchonta Cebus olivaceusHomo sapiens

Glires RattusLepus


Eulipotyphla Talpidae


Chiroptera Desmodontinae


Cetartiodactyla Capra walieEubalaena glacialis

Perissodactyla Equus quaggaDiceros bicornis


Pholidota Manidae

Carnivora Acinonyx jubatusZalophus californianus

The cladogram above is based on Tarver et al. (2016)[17]

Group I: Superorder Afrotheria[18]

Group II: Superorder Xenarthra[18]

  • Order Pilosa: sloths and anteaters (neotropical)
  • Order Cingulata: armadillos and extinct relatives (Americas)

Group III: Magnaorder Boreoeutheria[18]

Other Languages
Адыгэбзэ: ШэрыпӀхэр
Afrikaans: Soogdier
Alemannisch: Säugetiere
አማርኛ: ጡት አጥቢ
Ænglisc: Sycedēor
العربية: ثدييات
aragonés: Mammalia
asturianu: Mammalia
Avañe'ẽ: Okambúva
Aymar aru: Ñuñuri
azərbaycanca: Məməlilər
تۆرکجه: ممه‌لیلر
Bân-lâm-gú: Chhī-leng tōng-bu̍t
башҡортса: Һөтимәрҙәр
беларуская: Млекакормячыя
беларуская (тарашкевіца)‎: Сысуны
български: Бозайници
Boarisch: Spoviecha
bosanski: Sisari
brezhoneg: Bronneged
буряад: Хүхэтэн
català: Mamífers
Cebuano: Mamipero
čeština: Savci
chiShona: Dzinoyamwisa
corsu: Mammiferu
Cymraeg: Mamal
dansk: Pattedyr
Deutsch: Säugetiere
dolnoserbski: Cycaki
eesti: Imetajad
Ελληνικά: Θηλαστικό
español: Mammalia
Esperanto: Mamuloj
estremeñu: Mamíferu
euskara: Ugaztun
Fiji Hindi: Mammal
føroyskt: Súgdjór
français: Mammifère
Gaeilge: Mamach
Gaelg: Sheeintagh
Gàidhlig: Mamal
galego: Mamíferos
ГӀалгӀай: Дакхадийнаташ
Gĩkũyũ: Mammal
客家語/Hak-kâ-ngî: Sṳ̍t-nen thung-vu̍t
한국어: 포유류
հայերեն: Կաթնասուն
हिन्दी: स्तनधारी
hornjoserbsce: Cycaki
hrvatski: Sisavci
Ilokano: Mamalia
Bahasa Indonesia: Binatang menyusui
interlingua: Mammiferos
Interlingue: Mammiferes
ᐃᓄᒃᑎᑐᑦ/inuktitut: ᐱᓱᒃᑎ
íslenska: Spendýr
italiano: Mammalia
עברית: יונקים
Basa Jawa: Mamalia
ಕನ್ನಡ: ಸಸ್ತನಿ
Kapampangan: Mammal
kernowek: Bronnvil
Kiswahili: Mamalia
Kreyòl ayisyen: Mamifè
kurdî: Şîrmêj
Кыргызча: Сүт эмүүчү
Latina: Mammalia
latviešu: Zīdītāji
Lëtzebuergesch: Mamendéieren
lietuvių: Žinduoliai
Ligure: Mammalia
Limburgs: Zoogdiere
Lingua Franca Nova: Mamal
la .lojban.: mabru
lumbaart: Mamifer
magyar: Emlősök
македонски: Цицачи
മലയാളം: സസ്തനി
Malti: Mammiferu
მარგალური: ძუძუშმაწუალეფი
مصرى: ثدييات
Bahasa Melayu: Mamalia
Baso Minangkabau: Binatang manyusuan
Mìng-dĕ̤ng-ngṳ̄: Buô-ṳ̄ dông-ŭk
монгол: Хөхтөн
မြန်မာဘာသာ: နို့တိုက်သတ္တဝါ
Nederlands: Zoogdieren
Nedersaksies: Zoogdeers
日本語: 哺乳類
Napulitano: Mammifere
Nordfriisk: Tetjdiarten
norsk: Pattedyr
norsk nynorsk: Pattedyr
Nouormand: Mammiféthe
Novial: Mammalia
occitan: Mammalia
олык марий: Шӧр пукшышо
Oromoo: Hoosiftoota
oʻzbekcha/ўзбекча: Sut emizuvchilar
ਪੰਜਾਬੀ: ਥਣਧਾਰੀ
Pälzisch: Säugetiere
پنجابی: ددپلانے
Patois: Mamal
Перем Коми: Нимӧтчиссез
ភាសាខ្មែរ: ថនិកសត្វ
Piemontèis: Mamìfer
Plattdüütsch: Söögdeerten
polski: Ssaki
português: Mamíferos
română: Mamifer
rumantsch: Mammals
Runa Simi: Ñuñuq
русиньскый: Ссавцї
саха тыла: Кыыл
Gagana Samoa: Mamele
संस्कृतम्: सस्तनः
Scots: Mammal
Seeltersk: Suugedierte
shqip: Gjitari
sicilianu: Mammalia
Simple English: Mammal
سنڌي: مئمل
slovenčina: Cicavce
slovenščina: Sesalci
Soomaaliga: Naasley
کوردی: گوانداران
српски / srpski: Сисари
srpskohrvatski / српскохрватски: Sisavac
Basa Sunda: Mamalia
svenska: Däggdjur
Tagalog: Mamalya
தமிழ்: பாலூட்டி
татарча/tatarça: Имезүчеләр
తెలుగు: క్షీరదాలు
tetun: Mamíferu
тоҷикӣ: Ширхӯрон
Türkçe: Memeliler
удмурт: Пӧйшур
українська: Ссавці
اردو: ممالیہ
vèneto: Mamìfari
Tiếng Việt: Lớp Thú
Võro: Imetäjä
West-Vlams: Zoogbêestn
Winaray: Mammalia
吴语: 哺乳動物
ייִדיש: זויגער
粵語: 哺乳動物
Zazaki: Çıçeyıni
Zeêuws: Zoogdieren
žemaitėška: Žvierē
中文: 哺乳动物