Animal

Animals are <a href="/facts/Multicellular/rk8QBF7o">multicellular</a>, <a href="/facts/Eukaryotic/SkwyPLMA">eukaryotic</a> <a href="/facts/Organism/j8JkL09u">organisms</a> in the <a href="/facts/Biology/1M1ee3pB">biological</a> <a href="/facts/Kingdom_(biology)/QGRKbHos">kingdom</a> Animalia (/ˌænɪˈmeɪliə/). With few exceptions, animals <a href="/facts/Heterotroph/wtzlgBtz">organic material</a>, <a href="/facts/Cellular_respiration/kb6gpsvL">breathe oxygen</a>, have <a href="/facts/Myocyte/cP7Jea3q">myocytes</a> and are <a href="/facts/Motility/Df5BECHL">able to move</a>, can <a href="/facts/Reproduce_sexually/hmsXy53s">reproduce sexually</a>, and grow from a hollow sphere of <a href="/facts/Cell_(biology)/bLM9UQvy">cells</a>, the <a href="/facts/Blastula/sJVSBmbH">blastula</a>, during <a href="/facts/Embryonic_development/1lFY4EoW">embryonic development</a>. Animals form a <a href="/facts/Clade/XefyYmWn">clade</a>, meaning that they arose from a single <a href="/facts/Common_ancestor/bwEgMu7F">common ancestor</a>. Over 1.5 million <a href="/facts/Extant_taxon/YK8uj7qU">living</a> animal <a href="/facts/Species/oDg6b96r">species</a> have been <a href="/facts/Species_description/JyFpxSvJ">described</a>, of which around 1.05 million are <a href="/facts/Insect/IgDNvnUL">insects</a>, over 85,000 are <a href="/facts/Mollusc/1elgknsQ">molluscs</a>, and around 65,000 are <a href="/facts/Vertebrate/tT54FSTT">vertebrates</a>. It has been estimated there are as many as 7.77 million animal species on Earth. Animal body lengths range from 8.5 μm (0.00033 in) to 33.6 m (110 ft). They have complex <a href="/facts/Ecologies/YE8upuJU">ecologies</a> and <a href="/facts/Biological_interaction/uhcg3EaM">interactions</a> with each other and their environments, forming intricate <a href="/facts/Food_web/YaakLo08">food webs</a>. The scientific study of animals is known as <a href="/facts/Zoology/6Kj13mBt">zoology</a>, and the study of animal behaviour is known as <a href="/facts/Ethology/dM3CpysA">ethology</a>.
The animal kingdom is divided into five major clades, namely <a href="/facts/Porifera/E9T2WFWA">Porifera</a>, <a href="/facts/Ctenophora/3eGCj2e8">Ctenophora</a>, <a href="/facts/Placozoa/F9NcYdAz">Placozoa</a>, <a href="/facts/Cnidaria/d0HRc6w0">Cnidaria</a> and <a href="/facts/Bilateria/nfUwVYrx">Bilateria</a>. Most living animal species belong to the clade Bilateria, a highly proliferative clade whose members have a <a href="/facts/Bilaterally_symmetric/FSv5Sv4y">bilaterally symmetric</a> and significantly <a href="/facts/Cephalization/Ekw4Nd0a">cephalised</a> <a href="/facts/Body_plan/TykqU5bY">body plan</a>, and the vast majority of bilaterians belong to two large clades: the <a href="/facts/Protostome/XLtWYdt8">protostomes</a>, which includes organisms such as <a href="/facts/Arthropod/JKJLTFzp">arthropods</a>, <a href="/facts/Mollusc/1elgknsQ">molluscs</a>, <a href="/facts/Flatworm/lvqbrb2V">flatworms</a>, <a href="/facts/Annelid/PQvb7NAM">annelids</a> and <a href="/facts/Nematode/yLMJ43Eu">nematodes</a>; and the <a href="/facts/Deuterostome/Uc3V9mGA">deuterostomes</a>, which include <a href="/facts/Echinoderm/j2rd8qwt">echinoderms</a>, <a href="/facts/Hemichordate/51nn9BUX">hemichordates</a> and <a href="/facts/Chordate/AldL6ARm">chordates</a>, the latter of which contains the <a href="/facts/Vertebrate/tT54FSTT">vertebrates</a>. The much smaller <a href="/facts/Basal_(phylogenetics)/JQPQXpYg">basal</a> <a href="/facts/Phylum/ELT3Jyax">phylum</a> <a href="/facts/Xenacoelomorpha/TVSoSjU7">Xenacoelomorpha</a> have an uncertain position within Bilateria.
Animals first appeared in the fossil record in the late <a href="/facts/Cryogenian/5NxvCx4r">Cryogenian</a> period and diversified in the subsequent <a href="/facts/Ediacaran/z8jSUITT">Ediacaran</a> period in what is known as the <a href="/facts/Avalon_explosion/YCLcTMsW">Avalon explosion</a>. Earlier evidence of animals is still controversial; the <a href="/facts/Sponge/E9T2WFWA">sponge</a>-like organism <a href="/facts/Otavia/Qsq041rK">Otavia</a> has been dated back to the <a href="/facts/Tonian/qkGE6hCf">Tonian</a> period at the start of the <a href="/facts/Neoproterozoic/89NsnsM1">Neoproterozoic</a>, but its identity as an animal is heavily contested. Nearly all modern animal phyla first appeared in the fossil record as <a href="/facts/Marine_species/TF5MGzFb">marine species</a> during the <a href="/facts/Cambrian_explosion/Wg29M7PN">Cambrian explosion</a>, which began around 539 <a href="/facts/Million_years_ago/DXcnXuAw">million years ago</a> (Mya), and most <a href="/facts/Class_(biology)/a7MrgFu3">classes</a> during the <a href="/facts/Ordovician_radiation/z6wbnBnq">Ordovician radiation</a> 485.4 Mya. Common to all living animals, 6,331 groups of <a href="/facts/Gene/e1swwPY6">genes</a> have been identified that may have arisen from a single common ancestor that lived about 650 Mya during the <a href="/facts/Cryogenian/5NxvCx4r">Cryogenian</a> period.
Historically, <a href="/facts/Aristotle/U2bDlBFW">Aristotle</a> divided animals <a href="/facts/Aristotle%2527s_biology/jc8E4MBx">into those with blood and those without</a>. <a href="/facts/Carl_Linnaeus/gy5HWkHS">Carl Linnaeus</a> created the first hierarchical <a href="/facts/Biological_classification/Qkg8wuyw">biological classification</a> for animals in 1758 with his <a href="/facts/Systema_Naturae/8o4rU1DD">Systema Naturae</a>, which <a href="/facts/Jean-Baptiste_Lamarck/3lxaPmqM">Jean-Baptiste Lamarck</a> expanded into 14 phyla by 1809. In 1874, <a href="/facts/Ernst_Haeckel/osqrW7hB">Ernst Haeckel</a> divided the animal kingdom into the multicellular Metazoa (now <a href="/facts/Synonym_(taxonomy)/BHLdox7E">synonymous</a> with Animalia) and the <a href="/facts/Protozoa/JczTf25H">Protozoa</a>, single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as <a href="/facts/Molecular_phylogenetics/FysplHP5">molecular phylogenetics</a>, which are effective at demonstrating the <a href="/facts/Evolution/qE5amP6a">evolutionary</a> relationships between <a href="/facts/Taxa/caQC1e87">taxa</a>.
<a href="/facts/Human/rlcTENsr">Humans</a> make <a href="/facts/Human_uses_of_animals/zeo21evD">use of</a> many other animal species for <a href="/facts/Human_food/RgNq6NAK">food</a> (including <a href="/facts/Meat/DUHTTM1d">meat</a>, <a href="/facts/Eggs_as_food/dRLxAGev">eggs</a>, and <a href="/facts/Dairy_product/rGVJUHVb">dairy products</a>), for <a href="/facts/Animal_product/AFHGIGk8">materials</a> (such as <a href="/facts/Leather/kvQtwHPH">leather</a>, <a href="/facts/Fur/4hVxpDQ0">fur</a>, and <a href="/facts/Wool/AENKRTYl">wool</a>), as <a href="/facts/Pet/DIG0CzQ8">pets</a> and as <a href="/facts/Working_animal/LRENovAW">working animals</a> for <a href="/facts/Transportation/npstdhvc">transportation</a>, and <a href="/facts/Service_(economics)/B7L4tR8r">services</a>. <a href="/facts/Dog/DvQVRVzy">Dogs</a>, the first <a href="/facts/Domesticate/tWB5s52s">domesticated</a> animal, have been used <a href="/facts/Hunting_dog/Q2pjF4GF">in hunting</a>, <a href="/facts/Guard_dog/U75ECs59">in security</a> and <a href="/facts/Dogs_in_warfare/B2q0hX50">in warfare</a>, as have <a href="/facts/Equestrianism/F13lkV3E">horses</a>, <a href="/facts/Pigeon_post/JGwgAuEY">pigeons</a> and <a href="/facts/Falconry/GPvDJpkT">birds of prey</a>; while other <a href="/facts/Terrestrial_animal/AhP2mont">terrestrial</a> and <a href="/facts/Aquatic_animal/tY7gyRWl">aquatic animals</a> are <a href="/facts/Hunt/z1XhJdB2">hunted</a> for sports, trophies or profits. Non-human animals are also an important <a href="/facts/Cultural/c5JgMqpX">cultural</a> element of <a href="/facts/Human_evolution/DNzlDyKe">human evolution</a>, having appeared in <a href="/facts/Cave_art/yv2BehGH">cave arts</a> and <a href="/facts/Totem/I9YJhRSr">totems</a> since the earliest times, and are frequently featured in <a href="/facts/Mythology/kG8UTfem">mythology</a>, <a href="/facts/Religion/cxntrD0R">religion</a>, <a href="/facts/Art/6snb7Ixz">arts</a>, <a href="/facts/Literature/CmUDxokU">literature</a>, <a href="/facts/Heraldry/cmkn0H85">heraldry</a>, <a href="/facts/Politics/1gDNy3RP">politics</a>, and <a href="/facts/Sport/0NazHJMC">sports</a>.

Animal open-in-new

Animal