Mammal

A mammal is a <a href="/facts/Vertebrate/tT54FSTT">vertebrate</a> animal of the <a href="/facts/Class_(biology)/a7MrgFu3">class</a> Mammalia (/məˈmeɪli.ə/). Mammals are characterised by the presence of <a href="/facts/Milk/wDJBUHvy">milk</a>-producing <a href="/facts/Mammary_gland/6fVBnNSA">mammary glands</a> for feeding their young, a broad <a href="/facts/Neocortex/YEVjPgGK">neocortex</a> region of the brain, <a href="/facts/Fur/4hVxpDQ0">fur</a> or <a href="/facts/Hair/L7vt9FL3">hair</a>, and three <a href="/facts/Evolution_of_mammalian_auditory_ossicles/QaIQKcRu">middle ear bones</a>. These characteristics distinguish them from <a href="/facts/Reptile/04n1uKf1">reptiles</a> and <a href="/facts/Bird/RJF6zwLP">birds</a>, from which their ancestors <a href="/facts/Genetic_divergence/s4Hl2oe2">diverged</a> in the <a href="/facts/Carboniferous/BRKlkYyd">Carboniferous</a> Period over 300 million years ago. Around 6,640 <a href="/facts/Neontology/YK8uj7qU">extant</a> species of mammals have been described and divided into 27 <a href="/facts/Order_(biology)/GKLJvIpt">orders</a>. The study of mammals is called <a href="/facts/Mammalogy/C9d4Me2Q">mammalogy</a>.
The largest orders of mammals, by number of <a href="/facts/Species/oDg6b96r">species</a>, are the <a href="/facts/Rodent/mT4m8QJq">rodents</a>, <a href="/facts/Bat/CJudzNt1">bats</a>, and <a href="/facts/Eulipotyphla/aRE1FC8P">eulipotyphlans</a> (including <a href="/facts/Hedgehog/t0B8ft9X">hedgehogs</a>, <a href="/facts/Mole_(animal)/tunKPGPu">moles</a> and <a href="/facts/Shrew/FqIA64gX">shrews</a>). The next three are the <a href="/facts/Primate/Hl8RNE2X">primates</a> (including <a href="/facts/Human/rlcTENsr">humans</a>, <a href="/facts/Monkey/ARjd5RRr">monkeys</a> and <a href="/facts/Lemur/lgLEmFnr">lemurs</a>), the <a href="/facts/Artiodactyl/LS4ra9ET">even-toed ungulates</a> (including <a href="/facts/Pig/b5wxwdDY">pigs</a>, <a href="/facts/Camel/UGvEayFf">camels</a>, and <a href="/facts/Whale/EMJBgXfb">whales</a>), and the <a href="/facts/Carnivora/4wWDW8RY">Carnivora</a> (including <a href="/facts/Felidae/Fryfw7gm">cats</a>, <a href="/facts/Canidae/5Fj02eeS">dogs</a>, and <a href="/facts/Pinniped/8ya4Lzek">seals</a>).
Mammals are the only living members of <a href="/facts/Synapsida/uzYVtB0F">Synapsida</a>; this <a href="/facts/Clade/XefyYmWn">clade</a>, together with <a href="/facts/Sauropsida/70F7LGbt">Sauropsida</a> (reptiles and birds), constitutes the larger <a href="/facts/Amniote/TeLtDTrJ">Amniota</a> clade. Early synapsids are referred to as "<a href="/facts/Pelycosaur/hXU6TAxB">pelycosaurs</a>." The more advanced <a href="/facts/Therapsida/P4ERDjA2">therapsids</a> became dominant during the <a href="/facts/Guadalupian/rsksJLtV">Guadalupian</a>. Mammals originated from <a href="/facts/Cynodontia/8Trvx14s">cynodonts</a>, an advanced group of therapsids, during the Late <a href="/facts/Triassic/r6CNxKXC">Triassic</a> to Early <a href="/facts/Jurassic/o5Cy4KzX">Jurassic</a>. Mammals achieved their modern diversity in the <a href="/facts/Paleogene/CNsEpdA4">Paleogene</a> and <a href="/facts/Neogene/zUJxvjuH">Neogene</a> periods of the <a href="/facts/Cenozoic/yFslcz6n">Cenozoic</a> era, after the <a href="/facts/Cretaceous%25E2%2580%2593Paleogene_extinction_event/HNyDuEcx">extinction of non-avian dinosaurs</a>, and have been the <a href="/facts/Dominance_(ecology)/uqRC9f4s">dominant</a> terrestrial animal group from 66 million years ago to the present.
The basic mammalian body type is <a href="/facts/Quadrupedalism/KMVYdsYf">quadrupedal</a>, with most mammals using four <a href="/facts/Limb_(anatomy)/AqasUdSC">limbs</a> for <a href="/facts/Terrestrial_locomotion/HR8wosRh">terrestrial locomotion</a>; but in some, the limbs are adapted for life <a href="/facts/Marine_mammal/WCoC2ye8">at sea</a>, <a href="/facts/Flying_and_gliding_animals/dzTJgy86">in the air</a>, <a href="/facts/Arboreal_locomotion/6C5AeQ2y">in trees</a> or <a href="/facts/Fossorial/98TbrC3h">underground</a>. The <a href="/facts/Bipedalism/tvLMG77t">bipeds</a> have adapted to move using only the two lower limbs, while the rear limbs of <a href="/facts/Cetacea/rtC33h63">cetaceans</a> and the <a href="/facts/Sirenia/6KaaDKu5">sea cows</a> are mere internal <a href="/facts/Vestigiality/sYfUsCQX">vestiges</a>. Mammals range in size from the 30–40 millimetres (1.2–1.6 in) <a href="/facts/Bumblebee_bat/G9V4EDz7">bumblebee bat</a> to the 30 metres (98 ft) <a href="/facts/Blue_whale/CSlRTeCf">blue whale</a>—possibly the largest animal to have ever lived. Maximum lifespan varies from two years for the shrew to 211 years for the <a href="/facts/Bowhead_whale/JswW9AsW">bowhead whale</a>. All modern mammals give birth to live young, except the five species of <a href="/facts/Monotreme/fLMJM4JU">monotremes</a>, which lay eggs. The most species-rich group is the <a href="/facts/Viviparity/EEMn4rVx">viviparous</a> <a href="/facts/Placentalia/xegVWIRG">placental mammals</a>, so named for the temporary organ (<a href="/facts/Placenta/7XUoks1b">placenta</a>) used by offspring to draw nutrition from the mother during <a href="/facts/Gestation/QKgkykw5">gestation</a>.
Most mammals are <a href="/facts/Animal_cognition/LpP3H18I">intelligent</a>, with some possessing large brains, <a href="/facts/Self-awareness/e3Wh7bFx">self-awareness</a>, and <a href="/facts/Tool_use_by_non-humans/F0RnHLJj">tool use</a>. Mammals can communicate and vocalise in several ways, including the production of <a href="/facts/Ultrasound/31Pa5IH9">ultrasound</a>, <a href="/facts/Territory_(animal)/T15S7XeD">scent marking</a>, <a href="/facts/Alarm_signal/oWWJWhbU">alarm signals</a>, <a href="/facts/Animal_song/YAnwQhXp">singing</a>, <a href="/facts/Animal_echolocation/2hggutJV">echolocation</a>; and, in the case of humans, complex <a href="/facts/Language/IRcTok2q">language</a>. Mammals can organise themselves into <a href="/facts/Fission%25E2%2580%2593fusion_society/L21HWIeB">fission–fusion societies</a>, <a href="/facts/Harem_(zoology)/V4dCP2kP">harems</a>, and <a href="/facts/Hierarchy/mYJyqFrG">hierarchies</a>—but can also be solitary and <a href="/facts/Territory_(animal)/T15S7XeD">territorial</a>. Most mammals are <a href="/facts/Polygyny_in_animals/9QVUtGHj">polygynous</a>, but some can be <a href="/facts/Monogamy_in_animals/AvmMepzc">monogamous</a> or <a href="/facts/Polyandry_in_animals/5G7wxRme">polyandrous</a>.
<a href="/facts/Domestication/tWB5s52s">Domestication</a> of many types of mammals by humans played a major role in the <a href="/facts/Neolithic_Revolution/P5tLdcgU">Neolithic Revolution</a>, and resulted in <a href="/facts/Agriculture/TGztqzJs">farming</a> replacing <a href="/facts/Hunter-gatherer/ghnjoNbJ">hunting and gathering</a> as the primary source of food for humans. This led to a major restructuring of human societies from nomadic to sedentary, with more co-operation among larger and larger groups, and ultimately the development of the first <a href="/facts/Civilisation/xvGpjDPj">civilisations</a>. Domesticated mammals provided, and continue to provide, power for transport and agriculture, as well as food (<a href="/facts/Meat/DUHTTM1d">meat</a> and <a href="/facts/Dairy_product/rGVJUHVb">dairy products</a>), <a href="/facts/Fur/4hVxpDQ0">fur</a>, and <a href="/facts/Leather/kvQtwHPH">leather</a>. Mammals are also <a href="/facts/Hunting/z1XhJdB2">hunted</a> and raced for sport, kept as <a href="/facts/Pet/vE9Qj8dR">pets</a> and <a href="/facts/Working_animal/LRENovAW">working animals</a> of various types, and are used as <a href="/facts/Model_organism/vNv6q4yb">model organisms</a> in science. Mammals have been depicted in <a href="/facts/Art/ILbnQHHb">art</a> since <a href="/facts/Paleolithic/I48SMHo5">Paleolithic</a> times, and appear in literature, film, mythology, and religion. Decline in numbers and <a href="/facts/Extinction/24p5NP2q">extinction</a> of many mammals is primarily driven by human <a href="/facts/Poaching/UgYKJV0E">poaching</a> and <a href="/facts/Habitat_destruction/pyPMkBCY">habitat destruction</a>, primarily <a href="/facts/Deforestation/L1TNhN9p">deforestation</a>.

Mammal open-in-new

Mammal