Animal#History of classification

The word animal comes from the Latin noun {{Wikt-lang|la|animal}} of the same meaning, which is itself derived from Latin {{Wikt-lang|la|animalis}} 'having breath or soul'.{{cite dictionary |last=Cresswell |first=Julia |dictionary=The Oxford Dictionary of Word Origins |year=2010 |publisher=Oxford University Press |location=New York |edition=2nd |isbn=978-0-19-954793-7 |entry=Animal |quote='having the breath of life', from anima 'air, breath, life'.}} The biological definition includes all members of the kingdom Animalia.{{cite dictionary |title=Animal |dictionary=The American Heritage Dictionary |publisher=Houghton Mifflin |year=2006 |edition=4th}} In colloquial usage, the term animal is often used to refer only to nonhuman animals.{{cite dictionary |dictionary=English Oxford Living Dictionaries |title=Animal |url=https://en.oxforddictionaries.com/definition/animal |access-date=26 July 2018 |archive-url=https://web.archive.org/web/20180726233938/https://en.oxforddictionaries.com/definition/animal |archive-date=26 July 2018 |url-status=dead}}{{cite journal |last1=Boly |first1=Melanie |last2=Seth |first2=Anil K. |last3=Wilke |first3=Melanie |last4=Ingmundson |first4=Paul |last5=Baars |first5=Bernard |last6=Laureys |first6=Steven |last7=Edelman |first7=David |last8=Tsuchiya |first8=Naotsugu |display-authors=5 |year=2013 |title=Consciousness in humans and non-human animals: recent advances and future directions |journal=Frontiers in Psychology |volume=4 |page=625 |doi=10.3389/fpsyg.2013.00625 |pmc=3814086 |pmid=24198791 |doi-access=free}}{{Cite web |website=Royal Society |url=https://royalsociety.org/topics-policy/publications/2004/non-human-animals/ |title=The use of non-human animals in research |access-date=7 June 2018 |archive-url=https://web.archive.org/web/20180612140908/https://royalsociety.org/topics-policy/publications/2004/non-human-animals/ |archive-date=12 June 2018 |url-status=live}}{{Cite dictionary |url=https://www.collinsdictionary.com/dictionary/english/nonhuman |title=Nonhuman |dictionary=Collins English Dictionary |access-date=7 June 2018 |archive-url=https://web.archive.org/web/20180612142932/https://www.collinsdictionary.com/dictionary/english/nonhuman |archive-date=12 June 2018 |url-status=live}} The term metazoa is derived from Ancient Greek {{lang|grc|μετα}} {{tlit|grc|meta}} 'after' (in biology, the prefix meta- stands for 'later') and {{lang|grc|ζῷᾰ}} {{tlit|grc|zōia}} 'animals', plural of {{lang|grc|ζῷον}} {{tlit|grc|zōion}} 'animal'.{{cite dictionary |title=Metazoan |dictionary=Merriam-Webster |url=https://www.merriam-webster.com/dictionary/metazoan |access-date=6 July 2022 |archive-date=6 July 2022 |archive-url=https://web.archive.org/web/20220706115538/https://www.merriam-webster.com/dictionary/metazoan |url-status=live}}{{cite dictionary |title=Metazoa |dictionary=Collins |url=https://www.collinsdictionary.com/ko/dictionary/english/metazoa |access-date=6 July 2022 |archive-date=30 July 2022 |archive-url=https://web.archive.org/web/20220730091429/https://www.collinsdictionary.com/ko/dictionary/english/metazoa |url-status=live}} and further [https://www.collinsdictionary.com/ko/dictionary/english/meta meta- (sense 1)] {{Webarchive|url=https://web.archive.org/web/20220730091429/https://www.collinsdictionary.com/ko/dictionary/english/meta |date=30 July 2022 }} and [https://www.collinsdictionary.com/ko/dictionary/english/zoa -zoa] {{Webarchive|url=https://web.archive.org/web/20220730091429/https://www.collinsdictionary.com/ko/dictionary/english/zoa |date=30 July 2022 }}.

File:Blastulation.png (1) develop into a hollow ball or blastula (2).]]

Animals have several characteristics that they share with other living things. Animals are eukaryotic, multicellular, and aerobic, as are plants and fungi.{{cite book |last=Avila |first=Vernon L. |title=Biology: Investigating Life on Earth |url={{GBurl |id=B_OOazzGefEC |p=767}} |year=1995 |publisher=Jones & Bartlett |isbn=978-0-86720-942-6 |page=767}} Unlike plants and algae, which produce their own food,{{cite web |last=Davidson |first=Michael W. |title=Animal Cell Structure |url=https://micro.magnet.fsu.edu/cells/animalcell.html |access-date=20 September 2007 |archive-url=https://web.archive.org/web/20070920235924/https://micro.magnet.fsu.edu/cells/animalcell.html |archive-date=20 September 2007 |url-status=live}} animals cannot produce their own food{{cite web |title=Palaeos:Metazoa |url=https://palaeos.com/metazoa/metazoa.html |website=Palaeos |access-date=25 February 2018 |archive-url=https://web.archive.org/web/20180228005641/https://palaeos.com/metazoa/metazoa.html |archive-date=28 February 2018 |url-status=dead}}{{cite web |last=Bergman |first=Jennifer |title=Heterotrophs |url=https://www.windows.ucar.edu/tour/link=/earth/Life/heterotrophs.html&edu=high |access-date=30 September 2007 |archive-url=https://web.archive.org/web/20070829051950/https://www.windows.ucar.edu/tour/link%3D/earth/Life/heterotrophs.html%26edu%3Dhigh |archive-date=29 August 2007 |url-status=dead}} a feature they share with fungi. Animals ingest organic material and digest it internally.{{cite journal |last1=Douglas |first1=Angela E. |last2=Raven |first2=John A. |title=Genomes at the interface between bacteria and organelles |journal=Philosophical Transactions of the Royal Society B |volume=358 |issue=1429 |pages=5–17 |date=January 2003 |pmid=12594915 |pmc=1693093 |doi=10.1098/rstb.2002.1188}}

Animals have structural characteristics that set them apart from all other living things:

• cells surrounded by an extracellular matrix composed of
• collagen{{cite book |last1=Alberts |first1=Bruce |last2=Johnson |first2=Alexander |last3=Lewis |first3=Julian |last4=Raff |first4=Martin |last5=Roberts |first5=Keith |last6=Walter |first6=Peter |title=Molecular Biology of the Cell |edition=4th |year=2002 |publisher=Garland Science |url=https://www.ncbi.nlm.nih.gov/books/NBK26810/ |isbn=978-0-8153-3218-3 |access-date=29 August 2017 |archive-url=https://web.archive.org/web/20161223074013/https://www.ncbi.nlm.nih.gov/books/NBK26810/ |archive-date=23 December 2016 |url-status=live}} and
• elastic glycoproteins{{cite journal |last1=Heino |first1=Jyrki |last2=Huhtala |first2=Mikko |last3=Käpylä |first3=Jarmo |last4=Johnson |first4=Mark S. |title=Evolution of collagen-based adhesion systems |journal=The International Journal of Biochemistry & Cell Biology |date=February 2009 |volume=41 |issue=2 |pages=341–348 |doi=10.1016/j.biocel.2008.08.021|pmid=18790075 }}{{cite book |last1=Alberts |first1=Bruce |last2=Johnson |first2=Alexander |last3=Lewis |first3=Julian |last4=Raff |first4=Martin |last5=Roberts |first5=Keith |last6=Walter |first6=Peter |title=Molecular Biology of the Cell |edition=4th |year=2002 |publisher=Garland Science |url=https://www.ncbi.nlm.nih.gov/books/NBK26810/ |isbn=978-0-8153-3218-3 |access-date=29 August 2017 |archive-url=https://web.archive.org/web/20161223074013/https://www.ncbi.nlm.nih.gov/books/NBK26810/ |archive-date=23 December 2016 |url-status=live}}

• motility{{cite web |url=https://employees.csbsju.edu/SSAUPE/biol116/Zoology/digestion.htm |last=Saupe |first=S. G. |title=Concepts of Biology |access-date=30 September 2007 |archive-url=https://web.archive.org/web/20071121084100/https://employees.csbsju.edu/SSAUPE/biol116/Zoology/digestion.htm |archive-date=21 November 2007 |url-status=live}} i.e. able to spontaneously move their bodies during at least part of their life cycle.

• a blastula stage during embryonic development{{cite book |last=Minkoff |first=Eli C. |title=Barron's EZ-101 Study Keys Series: Biology |year=2008 |publisher=Barron's Educational Series |isbn=978-0-7641-3920-8 |edition=2nd, revised |page=48}}

Typically, there is an internal digestive chamber with either one opening (in Ctenophora, Cnidaria, and flatworms) or two openings (in most bilaterians).{{cite book |last1=Hillmer |first1=Gero |last2=Lehmann |first2=Ulrich |translator-first=J. |translator-last=Lettau |title=Fossil Invertebrates |year=1983 |publisher=Cambridge University Press Archive |isbn=978-0-521-27028-1 |page=54 |url={{GBurl |id=9jE4AAAAIAAJ |p=54}} |access-date=8 January 2016}}

Animal development is controlled by Hox genes, which signal the times and places to develop structures such as body segments and limbs.{{cite journal |last1=Ryan |first1=Joseph F. |last2=Mazza |first2=Maureen E. |last3=Pang |first3=Kevin |last4=Matus |first4=David Q. |last5=Baxevanis |first5=Andreas D. |last6=Martindale |first6=Mark Q. |last7=Finnerty |first7=John R. |title=Pre-Bilaterian Origins of the Hox Cluster and the Hox Code: Evidence from the Sea Anemone, Nematostella vectensis |journal=PLOS ONE |volume=2 |issue=1 |date=24 January 2007 |doi=10.1371/journal.pone.0000153 |doi-access=free |page=e153|pmid=17252055 |pmc=1779807 |bibcode=2007PLoSO...2..153R }}{{cite journal |last1=de Rosa |first1=Renaud |last2=Grenier |first2=Jennifer K. |last3=Andreeva |first3=Tatiana |last4=Cook |first4=Charles E. |last5=Adoutte |first5=André |last6=Akam |first6=Michael |last7=Carroll |first7=Sean B. |last8=Balavoine |first8=Guillaume |title=Hox genes in brachiopods and priapulids and protostome evolution |journal=Nature |volume=399 |issue=6738 |date=1999 |issn=0028-0836 |doi=10.1038/21631 |pages=772–776|pmid=10391241 |bibcode=1999Natur.399..772D }}

During development, the animal extracellular matrix forms a relatively flexible framework upon which cells can move about and be reorganised into specialised tissues and organs, making the formation of complex structures possible, and allowing cells to be differentiated.{{cite book |last=Minkoff |first=Eli C. |title=Barron's EZ-101 Study Keys Series: Biology |year=2008 |publisher=Barron's Educational Series |isbn=978-0-7641-3920-8 |edition=2nd, revised |page=48}} The extracellular matrix may be calcified, forming structures such as shells, bones, and spicules.{{cite book |last=Sangwal |first=Keshra |title=Additives and crystallization processes: from fundamentals to applications |url=https://archive.org/details/additivescrystal00sang |url-access=limited |year=2007 |publisher=John Wiley & Sons |isbn=978-0-470-06153-4 |page=[https://archive.org/details/additivescrystal00sang/page/n228 212]}} In contrast, the cells of other multicellular organisms (primarily algae, plants, and fungi) are held in place by cell walls, and so develop by progressive growth.{{cite book |last=Becker |first=Wayne M. |title=The world of the cell |year=1991 |publisher=Benjamin Cummings |isbn=978-0-8053-0870-9 |url=https://archive.org/details/worldofcell00beck_0}}

{{see also|Sexual reproduction#Animals|Asexual reproduction#Examples in animals}}

File:Odonata copulation.jpg is nearly universal in animals, such as these dragonflies.]]

Nearly all animals make use of some form of sexual reproduction.{{cite book |last=Knobil |first=Ernst |title=Encyclopedia of reproduction |volume=1 |year=1998 |publisher=Academic |isbn=978-0-12-227020-8 |page=[https://archive.org/details/encyclopediaofre0000unse_f1r2/page/315 315] |url=https://archive.org/details/encyclopediaofre0000unse_f1r2/page/315}} They produce haploid gametes by meiosis; the smaller, motile gametes are spermatozoa and the larger, non-motile gametes are ova.{{cite book |last=Schwartz |first=Jill |title=Master the GED 2011 |year=2010 |publisher=Peterson's |isbn=978-0-7689-2885-3 |page=[https://archive.org/details/petersonsmasterg0000stew_x3f1/page/371 371] |url=https://archive.org/details/petersonsmasterg0000stew_x3f1/page/371}} These fuse to form zygotes,{{cite book |last=Hamilton |first=Matthew B. |title=Population genetics |url=https://archive.org/details/populationgeneti00hami |url-access=limited |year=2009 |publisher=Wiley-Blackwell |isbn=978-1-4051-3277-0 |page=[https://archive.org/details/populationgeneti00hami/page/n69 55]}} which develop via mitosis into a hollow sphere, called a blastula. In sponges, blastula larvae swim to a new location, attach to the seabed, and develop into a new sponge.{{cite book |last1=Ville |first1=Claude Alvin |last2=Walker |first2=Warren Franklin |last3=Barnes |first3=Robert D. |title=General zoology |year=1984 |publisher=Saunders College |isbn=978-0-03-062451-3 |page=467}} In most other groups, the blastula undergoes more complicated rearrangement.{{cite book |last1=Hamilton |first1=William James |last2=Boyd |first2=James Dixon |last3=Mossman |first3=Harland Winfield |title=Human embryology: (prenatal development of form and function) |year=1945 |publisher=Williams & Wilkins |page=330}} It first invaginates to form a gastrula with a digestive chamber and two separate germ layers, an external ectoderm and an internal endoderm.{{cite book |last=Philips |first=Joy B. |title=Development of vertebrate anatomy |year=1975 |publisher=Mosby |isbn=978-0-8016-3927-2 |page=[https://archive.org/details/developmentofver0000phil/page/176 176] |url=https://archive.org/details/developmentofver0000phil/page/176}} In most cases, a third germ layer, the mesoderm, also develops between them.{{cite book |title=The Encyclopedia Americana |volume=10 |year=1918 |page=281}} These germ layers then differentiate to form tissues and organs.{{cite book |last1=Romoser |first1=William S. |author-link1=William S. Romoser |last2=Stoffolano |first2=J. G. |title=The science of entomology |year=1998 |publisher=WCB McGraw-Hill |isbn=978-0-697-22848-2 |page=156}}

Repeated instances of mating with a close relative during sexual reproduction generally leads to inbreeding depression within a population due to the increased prevalence of harmful recessive traits.{{cite journal |last1=Charlesworth |first1=D. |last2=Willis |first2=J. H. |title=The genetics of inbreeding depression |journal=Nature Reviews Genetics |volume=10 |issue=11 |pages=783–796 |year=2009 |pmid=19834483 |doi=10.1038/nrg2664 |s2cid=771357}}{{cite book |last1=Bernstein |first1=H. |last2=Hopf |first2=F. A. |last3=Michod |first3=R. E. |chapter=The Molecular Basis of the Evolution of Sex |title=Molecular Genetics of Development |series=Advances in Genetics |volume=24 |pages=323–370 |year=1987 |pmid=3324702 |doi=10.1016/s0065-2660(08)60012-7 |isbn=978-0-12-017624-3}} Animals have evolved numerous mechanisms for avoiding close inbreeding.{{cite journal |last1=Pusey |first1=Anne |last2=Wolf |first2=Marisa |title=Inbreeding avoidance in animals |journal=Trends Ecol. Evol. |volume=11 |issue=5 |pages=201–206 |year=1996 |pmid=21237809 |doi=10.1016/0169-5347(96)10028-8 |bibcode=1996TEcoE..11..201P}}

Some animals are capable of asexual reproduction, which often results in a genetic clone of the parent. This may take place through fragmentation; budding, such as in Hydra and other cnidarians; or parthenogenesis, where fertile eggs are produced without mating, such as in aphids.{{cite book |last1=Adiyodi |first1=K. G. |title=Reproductive Biology of Invertebrates|last2=Hughes |first2=Roger N. |last3=Adiyodi |first3=Rita G. |date=July 2002 |publisher=Wiley |isbn=978-0-471-48968-9 |volume=11, Progress in Asexual Reproduction|page=116}}{{cite web |last1=Schatz |first1=Phil |title=Concepts of Biology: How Animals Reproduce |url=https://philschatz.com/biology-concepts-book/contents/m45547.html |publisher=OpenStax College |access-date=5 March 2018 |archive-url=https://web.archive.org/web/20180306022745/https://philschatz.com/biology-concepts-book/contents/m45547.html |archive-date=6 March 2018 |url-status=live}}

File:Ultramarine Flycatcher (Ficedula superciliaris) Naggar, Himachal Pradesh, 2013 (cropped).JPGs, such as this ultramarine flycatcher (Ficedula superciliaris), feed on other animals.]]

Animals are categorised into ecological groups depending on their trophic levels and how they consume organic material. Such groupings include carnivores (further divided into subcategories such as piscivores, insectivores, ovivores, etc.), herbivores (subcategorised into folivores, graminivores, frugivores, granivores, nectarivores, algivores, etc.), omnivores, fungivores, scavengers/detritivores,{{cite book |last1=Marchetti |first1=Mauro |last2=Rivas |first2=Victoria |title=Geomorphology and environmental impact assessment |year=2001 |publisher=Taylor & Francis |isbn=978-90-5809-344-8 |page=84}} and parasites.{{cite book |last=Levy |first=Charles K. |title=Elements of Biology |year=1973 |publisher=Appleton-Century-Crofts |isbn=978-0-390-55627-1 |page=108}} Interactions between animals of each biome form complex food webs within that ecosystem. In carnivorous or omnivorous species, predation is a consumer–resource interaction where the predator feeds on another organism, its prey,{{cite book |last1=Begon |first1=M. |last2=Townsend |first2=C. |last3=Harper |first3=J. |date=1996 |title=Ecology: Individuals, populations and communities |edition=3rd |publisher=Blackwell |isbn=978-0-86542-845-4 |url=https://archive.org/details/ecology00mich}} who often evolves anti-predator adaptations to avoid being fed upon. Selective pressures imposed on one another lead to an evolutionary arms race between predator and prey, resulting in various antagonistic/competitive coevolutions.{{cite book |last1=Allen |first1=Larry Glen |last2=Pondella |first2=Daniel J. |last3=Horn |first3=Michael H. |title=Ecology of marine fishes: California and adjacent waters |year=2006 |publisher=University of California Press |isbn=978-0-520-24653-9 |page=428}}{{cite book |last=Caro |first=Tim |author-link=Tim Caro |title=Antipredator Defenses in Birds and Mammals |year=2005 |publisher=University of Chicago Press |pages=1–6 and passim}} Almost all multicellular predators are animals.{{cite journal |last1=Simpson |first1=Alastair G. B. |last2=Roger |first2=Andrew J. |doi=10.1016/j.cub.2004.08.038 |pmid=15341755 |title=The real 'kingdoms' of eukaryotes |journal=Current Biology |volume=14 |issue=17 |pages=R693–R696 |year=2004 |s2cid=207051421 |doi-access=free |bibcode=2004CBio...14.R693S}} Some consumers use multiple methods; for example, in parasitoid wasps, the larvae feed on the hosts' living tissues, killing them in the process,{{cite journal |last=Stevens |first=Alison N. P. |title=Predation, Herbivory, and Parasitism |journal=Nature Education Knowledge |year=2010 |volume=3 |issue=10 |page=36 |url=https://www.nature.com/scitable/knowledge/library/predation-herbivory-and-parasitism-13261134 |access-date=12 February 2018 |archive-url=https://web.archive.org/web/20170930230324/https://www.nature.com/scitable/knowledge/library/predation-herbivory-and-parasitism-13261134 |archive-date=30 September 2017 |url-status=live}} but the adults primarily consume nectar from flowers.{{Cite journal |last1=Jervis |first1=M. A. |last2=Kidd |first2=N. A. C. |date=November 1986 |title=Host-Feeding Strategies in Hymenopteran Parasitoids |journal=Biological Reviews |volume=61 |issue=4 |pages=395–434 |doi=10.1111/j.1469-185x.1986.tb00660.x |s2cid=84430254}} Other animals may have very specific feeding behaviours, such as hawksbill sea turtles which mainly eat sponges.{{cite journal |last=Meylan |first=Anne |title=Spongivory in Hawksbill Turtles: A Diet of Glass |journal=Science |volume=239 |issue=4838 |pages=393–395 |date=22 January 1988 |doi=10.1126/science.239.4838.393 |pmid=17836872 |jstor=1700236 |bibcode=1988Sci...239..393M |s2cid=22971831}}

File:Expl0072 - Flickr - NOAA Photo Library.jpg mussels and shrimps]]

Most animals rely on biomass and bioenergy produced by plants and phytoplanktons (collectively called producers) through photosynthesis. Herbivores, as primary consumers, eat the plant material directly to digest and absorb the nutrients, while carnivores and other animals on higher trophic levels indirectly acquire the nutrients by eating the herbivores or other animals that have eaten the herbivores. Animals oxidise carbohydrates, lipids, proteins and other biomolecules, which allows the animal to grow and to sustain basal metabolism and fuel other biological processes such as locomotion.{{cite book |title=Understanding Science: Upper Primary |last=Clutterbuck |first=Peter |year=2000 |publisher=Blake |isbn=978-1-86509-170-9 |page=9}}{{cite book |last1=Garrett |first1=Reginald |last2=Grisham |first2=Charles M. |title=Biochemistry |url=https://archive.org/details/biochemistry00rhga |url-access=limited |year=2010 |publisher=Cengage |isbn=978-0-495-10935-8 |page=[https://archive.org/details/biochemistry00rhga/page/n572 535]}} Some benthic animals living close to hydrothermal vents and cold seeps on the dark sea floor consume organic matter produced through chemosynthesis (via oxidising inorganic compounds such as hydrogen sulfide) by archaea and bacteria.{{cite book |last1=Castro |first1=Peter |last2=Huber |first2=Michael E. |title=Marine Biology |publisher=McGraw Hill |year=2007 |edition=7th |page=376 |isbn=978-0-07-722124-9}}

Animals evolved in the sea. Lineages of arthropods colonised land around the same time as land plants, probably between 510 and 471 million years ago during the Late Cambrian or Early Ordovician.{{cite journal |last1=Rota-Stabelli |first1=Omar |last2=Daley |first2=Allison C. |last3=Pisani |first3=Davide |title=Molecular Timetrees Reveal a Cambrian Colonization of Land and a New Scenario for Ecdysozoan Evolution |journal=Current Biology |volume=23 |issue=5 |pages=392–398 |year=2013 |doi-access=free |doi=10.1016/j.cub.2013.01.026 |pmid=23375891 |bibcode=2013CBio...23..392R}} Vertebrates such as the lobe-finned fish Tiktaalik started to move on to land in the late Devonian, about 375 million years ago.{{cite journal |last1=Daeschler |first1=Edward B. |last2=Shubin |first2=Neil H. |last3=Jenkins |first3=Farish A. Jr. |title=A Devonian tetrapod-like fish and the evolution of the tetrapod body plan |journal=Nature |volume=440 |pages=757–763 |date=6 April 2006 |doi=10.1038/nature04639 |pmid=16598249 |issue=7085 |bibcode=2006Natur.440..757D |doi-access=free}}{{cite journal |author-link=Jennifer A. Clack |last=Clack |first=Jennifer A. |journal=Scientific American |volume=293 |issue=6 |pages=100–107 |title=Getting a Leg Up on Land |date=21 November 2005 |bibcode=2005SciAm.293f.100C |doi=10.1038/scientificamerican1205-100 |pmid=16323697}} Animals occupy virtually all of earth's habitats and microhabitats, with faunas adapted to salt water, hydrothermal vents, fresh water, hot springs, swamps, forests, pastures, deserts, air, and the interiors of other organisms.{{cite book |last=Margulis |first=Lynn |author1-link=Lynn Margulis |author2=Schwartz, Karlene V. |author3=Dolan, Michael |title=Diversity of Life: The Illustrated Guide to the Five Kingdoms |url={{GBurl |id=8wJXWBMsEOkC |p=115}} |year=1999 |publisher=Jones & Bartlett |isbn=978-0-7637-0862-7 |pages=115–116}} Animals are however not particularly heat tolerant; very few of them can survive at constant temperatures above {{convert|50|°C|0|abbr=on}}{{cite journal |last=Clarke |first=Andrew |title=The thermal limits to life on Earth |journal=International Journal of Astrobiology |volume=13 |issue=2 |pages=141–154 |year=2014 |bibcode=2014IJAsB..13..141C |url=https://nora.nerc.ac.uk/id/eprint/507274/1/Clarke.pdf |archive-url=https://web.archive.org/web/20190424155004/https://nora.nerc.ac.uk/id/eprint/507274/1/Clarke.pdf |archive-date=24 April 2019 |url-status=live |doi=10.1017/S1473550413000438 |doi-access=free}} or in the most extreme cold deserts of continental Antarctica.{{cite web |title=Land animals |url=https://www.bas.ac.uk/about/antarctica/wildlife/land-animals/ |publisher=British Antarctic Survey |access-date=7 March 2018 |archive-url=https://web.archive.org/web/20181106225451/https://www.bas.ac.uk/about/antarctica/wildlife/land-animals/ |archive-date=6 November 2018 |url-status=live}}

The collective global geomorphic influence of animals on the processes shaping the Earth's surface remains largely understudied, with most studies limited to individual species and well-known exemplars.{{Cite journal |last1=Harvey |first1=Gemma L. |last2=Khan |first2=Zareena |last3=Albertson |first3=Lindsey K. |last4=Coombes |first4=Martin |last5=Johnson |first5=Matthew F. |last6=Rice |first6=Stephen P. |last7=Viles |first7=Heather A. |date=2025-02-25 |title=Global diversity and energy of animals shaping the Earth's surface |url=https://pubmed.ncbi.nlm.nih.gov/39964729/ |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=122 |issue=8 |pages=e2415104122 |doi=10.1073/pnas.2415104122 |issn=1091-6490 |pmid=39964729|pmc=11874378 |pmc-embargo-date=August 18, 2025 }}

{{further|Largest organisms|Smallest organisms}}

The blue whale (Balaenoptera musculus) is the largest animal that has ever lived, weighing up to 190 tonnes and measuring up to {{convert|33.6|m|ft}} long.{{cite book |last=Wood |first=Gerald |title=The Guinness Book of Animal Facts and Feats |year=1983 |isbn=978-0-85112-235-9 |url=https://archive.org/details/guinnessbookofan00wood |publisher=Guinness Superlatives |location=Enfield, Middlesex}}{{cite news |last1=Davies |first1=Ella |title=The longest animal alive may be one you never thought of |url=https://www.bbc.com/earth/story/20160420-the-longest-animal-alive-may-not-be-the-blue-whale |work=BBC Earth |access-date=1 March 2018 |date=20 April 2016 |archive-url=https://web.archive.org/web/20180319073808/https://www.bbc.com/earth/story/20160420-the-longest-animal-alive-may-not-be-the-blue-whale |archive-date=19 March 2018 |url-status=live}} The largest extant terrestrial animal is the African bush elephant (Loxodonta africana), weighing up to 12.25 tonnes and measuring up to {{convert|10.67|m|ft}} long. The largest terrestrial animals that ever lived were titanosaur sauropod dinosaurs such as Argentinosaurus, which may have weighed as much as 73 tonnes, and Supersaurus which may have reached 39 metres.{{cite journal |last1=Mazzetta |first1=Gerardo V. |last2=Christiansen |first2=Per |last3=Fariña |first3=Richard A. |year=2004 |title=Giants and Bizarres: Body Size of Some Southern South American Cretaceous Dinosaurs |journal=Historical Biology |volume=16 |issue=2–4 |pages=71–83 |doi=10.1080/08912960410001715132 |bibcode=2004HBio...16...71M |citeseerx=10.1.1.694.1650 |s2cid=56028251}}{{Cite conference |last=Curtice |first=Brian |year=2020 |conference=Society of Vertebrate Paleontology |url=https://vertpaleo.org/wp-content/uploads/2021/10/SVP_2021_VirtualBook_final.pdf#page=92 |title=Dinosaur Systematics, Diversity, & Biology |access-date=30 December 2022 |archive-date=19 October 2021 |archive-url=https://web.archive.org/web/20211019192436/https://vertpaleo.org/wp-content/uploads/2021/10/SVP_2021_VirtualBook_final.pdf#page=92 |url-status=live |page=92}} Several animals are microscopic; some Myxozoa (obligate parasites within the Cnidaria) never grow larger than 20 μm,{{cite web |url=https://tolweb.org/Myxozoa/2460/2008.07.10 |title=Myxozoa |last=Fiala |first=Ivan |date=10 July 2008 |publisher=Tree of Life Web Project |access-date=4 March 2018 |archive-url=https://web.archive.org/web/20180301225416/https://tolweb.org/Myxozoa/2460/2008.07.10 |archive-date=1 March 2018 |url-status=live}} and one of the smallest species (Myxobolus shekel) is no more than 8.5 μm when fully grown.{{cite journal |last1=Kaur |first1=H. |last2=Singh |first2=R. |title=Two new species of Myxobolus (Myxozoa: Myxosporea: Bivalvulida) infecting an Indian major carp and a cat fish in wetlands of Punjab, India |pmc=3235390 |pmid=23024499 |doi=10.1007/s12639-011-0061-4 |volume=35 |issue=2 |year=2011 |journal=Journal of Parasitic Diseases |pages=169–176}}

File:Anim1754 - Flickr - NOAA Photo Library (1).jpg|The blue whale is the largest animal that has ever lived; it can be up to {{convert|33.6|m|ft}} long.

File:Fdl17-9-grey.jpg|Myxozoans such as Myxobolus cerebralis are single-celled parasites, never more than 20 μm across.

The following table lists estimated numbers of described extant species for the major animal phyla,{{cite journal |last=Zhang |first=Zhi-Qiang |title=Animal biodiversity: An update of classification and diversity in 2013 |publisher=Magnolia Press |journal=Zootaxa |volume=3703 |issue=1 |date=30 August 2013 |doi=10.11646/zootaxa.3703.1.3 |url=https://biotaxa.org/Zootaxa/article/download/zootaxa.3703.1.3/4273 |page=5 |access-date=2 March 2018 |archive-url=https://web.archive.org/web/20190424154926/https://biotaxa.org/Zootaxa/article/download/zootaxa.3703.1.3/4273 |archive-date=24 April 2019 |url-status=live |doi-access=free}} along with their principal habitats (terrestrial, fresh water,{{cite book |last1=Balian |first1=E. V. |last2=Lévêque |first2=C. |last3=Segers |first3=H. |first4=K. |last4=Martens |title=Freshwater Animal Diversity Assessment |url={{GBurl |id=Dw4H6DBHnAgC |p=628}} |year=2008 |publisher=Springer |isbn=978-1-4020-8259-7 |page=628}} and marine),{{cite web |last1=Hogenboom |first1=Melissa |title=There are only 35 kinds of animal and most are really weird |url=https://www.bbc.co.uk/earth/story/20150325-all-animal-life-in-35-photos |publisher=BBC Earth |access-date=2 March 2018 |archive-url=https://web.archive.org/web/20180810141811/https://www.bbc.co.uk/earth/story/20150325-all-animal-life-in-35-photos |archive-date=10 August 2018 |url-status=live}} and free-living or parasitic ways of life.{{cite book |last=Poulin |first=Robert |author-link=Robert Poulin (zoologist) |title=Evolutionary Ecology of Parasites |publisher=Princeton University Press |year=2007 |isbn=978-0-691-12085-0 |page=[https://archive.org/details/evolutionaryecol0000poul/page/6 6] |url=https://archive.org/details/evolutionaryecol0000poul/page/6}} Species estimates shown here are based on numbers described scientifically; much larger estimates have been calculated based on various means of prediction, and these can vary wildly. For instance, around 25,000–27,000 species of nematodes have been described, while published estimates of the total number of nematode species include 10,000–20,000; 500,000; 10 million; and 100 million.{{cite book |last1=Felder |first1=Darryl L. |last2=Camp |first2=David K. |title=Gulf of Mexico Origin, Waters, and Biota: Biodiversity |url={{GBurl |id=CphA8hiwaFIC |pg=RA1-PA1111}} |year=2009 |publisher=Texas A&M University Press |isbn=978-1-60344-269-5 |page=1111}} Using patterns within the taxonomic hierarchy, the total number of animal species—including those not yet described—was calculated to be about 7.77 million in 2011.{{cite web |title=How many species on Earth? About 8.7 million, new estimate says |url=https://www.sciencedaily.com/releases/2011/08/110823180459.htm |access-date=2 March 2018 |date=24 August 2011 |archive-url=https://web.archive.org/web/20180701164954/https://www.sciencedaily.com/releases/2011/08/110823180459.htm |archive-date=1 July 2018 |url-status=live}}{{cite journal |last1=Mora |first1=Camilo |last2=Tittensor |first2=Derek P. |last3=Adl |first3=Sina |last4=Simpson |first4=Alastair G. B. |last5=Worm |first5=Boris |editor-last=Mace |editor-first=Georgina M. |title=How Many Species Are There on Earth and in the Ocean? |journal=PLOS Biology |volume=9 |issue=8 |date=23 August 2011 |doi=10.1371/journal.pbio.1001127 |page=e1001127 |pmid=21886479 |pmc=3160336 |doi-access=free}}{{efn|The application of DNA barcoding to taxonomy further complicates this; a 2016 barcoding analysis estimated a total count of nearly 100,000 insect species for Canada alone, and extrapolated that the global insect fauna must be in excess of 10 million species, of which nearly 2 million are in a single fly family known as gall midges (Cecidomyiidae).{{cite journal |last1=Hebert |first1=Paul D. N. |last2=Ratnasingham |first2=Sujeevan |last3=Zakharov |first3=Evgeny V. |last4=Telfer |first4=Angela C. |last5=Levesque-Beaudin |first5=Valerie |last6=Milton |first6=Megan A. |last7=Pedersen |first7=Stephanie |last8=Jannetta |first8=Paul |last9=deWaard |first9=Jeremy R. |display-authors=5 |title=Counting animal species with DNA barcodes: Canadian insects |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |date=1 August 2016 |volume=371 |issue=1702 |pages=20150333 |doi=10.1098/rstb.2015.0333 |pmid=27481785 |pmc=4971185}}}}

{{Further|Urmetazoan}}

Evidence of animals is found as long ago as the Cryogenian period. 24-Isopropylcholestane (24-ipc) has been found in rocks from roughly 650 million years ago; it is only produced by sponges and pelagophyte algae. Its likely origin is from sponges based on molecular clock estimates for the origin of 24-ipc production in both groups. Analyses of pelagophyte algae consistently recover a Phanerozoic origin, while analyses of sponges recover a Neoproterozoic origin, consistent with the appearance of 24-ipc in the fossil record.{{cite journal |last1=Gold |first1=David |display-authors=et al. |title=Sterol and genomic analyses validate the sponge biomarker hypothesis |journal=PNAS |date=22 February 2016 |volume=113 |issue=10 |pages=2684–2689 |doi=10.1073/pnas.1512614113 |doi-access=free |pmid=26903629 |pmc=4790988 |bibcode=2016PNAS..113.2684G}}{{cite journal |last1=Love |first1=Gordon |display-authors=et al. |title=Fossil steroids record the appearance of Demospongiae during the Cryogenian period |journal=Nature |date=5 February 2009 |volume=457 |issue=7230 |pages=718–721 |doi=10.1038/nature07673 |pmid=19194449 |bibcode=2009Natur.457..718L|url=https://resolver.caltech.edu/CaltechAUTHORS:20090807-101203081 }}

The first body fossils of animals appear in the Ediacaran, represented by forms such as Charnia and Spriggina. It had long been doubted whether these fossils truly represented animals,{{cite journal |last1=Shen |first1=Bing |last2=Dong |first2=Lin |last3=Xiao |first3=Shuhai |last4=Kowalewski |first4=Michał |year=2008 |title=The Avalon Explosion: Evolution of Ediacara Morphospace |journal=Science |volume=319 |issue=5859 |pages=81–84 |doi=10.1126/science.1150279 |pmid=18174439 |bibcode=2008Sci...319...81S |s2cid=206509488}}{{cite journal |title=Late Ediacaran trackways produced by bilaterian animals with paired appendages |first1=Zhe |last1=Chen |first2=Xiang |last2=Chen |first3=Chuanming |last3=Zhou |first4=Xunlai |last4=Yuan |first5=Shuhai |last5=Xiao |date=1 June 2018 |journal=Science Advances |volume=4 |issue=6 |pages=eaao6691 |doi=10.1126/sciadv.aao6691 |pmid=29881773 |pmc=5990303 |bibcode=2018SciA....4.6691C}}{{cite book |last=Schopf |first=J. William |title=Evolution!: facts and fallacies |year=1999 |publisher=Academic Press |isbn=978-0-12-628860-5 |page=[https://archive.org/details/evolutionfactsfa0000unse/page/7 7] |url=https://archive.org/details/evolutionfactsfa0000unse/page/7}} but the discovery of the animal lipid cholesterol in fossils of Dickinsonia establishes their nature. Animals are thought to have originated under low-oxygen conditions, suggesting that they were capable of living entirely by anaerobic respiration, but as they became specialised for aerobic metabolism they became fully dependent on oxygen in their environments.{{cite journal |last1=Zimorski |first1=Verena |last2=Mentel |first2=Marek |last3=Tielens |first3=Aloysius G. M. |last4=Martin |first4=William F. |title=Energy metabolism in anaerobic eukaryotes and Earth's late oxygenation |journal=Free Radical Biology and Medicine |volume=140 |pages=279–294 |year=2019 |doi=10.1016/j.freeradbiomed.2019.03.030 |pmid=30935869 |pmc=6856725}}

Many animal phyla first appear in the fossil record during the Cambrian explosion, starting about 539 million years ago, in beds such as the Burgess shale.{{cite web |title=Stratigraphic Chart 2022 |url=https://stratigraphy.org/ICSchart/ChronostratChart2022-02.pdf |publisher=International Stratigraphic Commission |date=February 2022 |access-date=25 April 2022 |archive-date=2 April 2022 |archive-url=https://web.archive.org/web/20220402100018/https://stratigraphy.org/ICSchart/ChronostratChart2022-02.pdf |url-status=live}} Extant phyla in these rocks include molluscs, brachiopods, onychophorans, tardigrades, arthropods, echinoderms and hemichordates, along with numerous now-extinct forms such as the predatory Anomalocaris. The apparent suddenness of the event may however be an artefact of the fossil record, rather than showing that all these animals appeared simultaneously.{{cite journal |last1=Maloof |first1=A. C. |last2=Porter |first2=S. M. |last3=Moore |first3=J. L. |last4=Dudas |first4=F. O. |last5=Bowring |first5=S. A. |last6=Higgins |first6=J. A. |last7=Fike |first7=D. A. |last8=Eddy |first8=M. P. |s2cid=6694681 |title=The earliest Cambrian record of animals and ocean geochemical change |journal=Geological Society of America Bulletin |year=2010 |volume=122 |issue=11–12 |pages=1731–1774 |doi=10.1130/B30346.1 |bibcode=2010GSAB..122.1731M}}{{cite web |title=New Timeline for Appearances of Skeletal Animals in Fossil Record Developed by UCSB Researchers |url=https://www.ia.ucsb.edu/pa/display.aspx?pkey=2364 |publisher=The Regents of the University of California |access-date=1 September 2014 |date=10 November 2010 |archive-url=https://web.archive.org/web/20140903062054/https://www.ia.ucsb.edu/pa/display.aspx?pkey=2364 |archive-date=3 September 2014 |url-status=live}}{{cite journal |last=Conway-Morris |first=Simon |author-link=Simon Conway Morris |title=The Cambrian "explosion" of metazoans and molecular biology: would Darwin be satisfied? |journal=The International Journal of Developmental Biology |year=2003 |volume=47 |issue=7–8 |pages=505–515 |pmid=14756326 |url=https://ijdb.ehu.eus/article/pdf/14756326 |access-date=28 September 2024 |archive-url=https://web.archive.org/web/20231114204853if_/https://ijdb.ehu.eus/article/pdf/14756326 |archive-date=14 November 2023 |url-status=live}}{{cite journal |last1=Morris |first1=Simon Conway |author-link=Simon Conway Morris |title=Darwin's dilemma: the realities of the Cambrian 'explosion'. |journal=Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences |date=29 June 2006 |volume=361 |issue=1470 |pages=1069–83 |doi=10.1098/rstb.2006.1846 |pmid=16754615 |pmc=1578734}}{{cite web |title=The Tree of Life |url=https://burgess-shale.rom.on.ca/en/science/origin/01-life-tree.php |website=The Burgess Shale |publisher=Royal Ontario Museum |access-date=28 February 2018 |archive-url=https://web.archive.org/web/20180216054845/https://burgess-shale.rom.on.ca/en/science/origin/01-life-tree.php |archive-date=16 February 2018 |url-status=dead |date=10 June 2011}} That view is supported by the discovery of Auroralumina attenboroughii, the earliest known Ediacaran crown-group cnidarian (557–562 mya, some 20 million years before the Cambrian explosion) from Charnwood Forest, England. It is thought to be one of the earliest predators, catching small prey with its nematocysts as modern cnidarians do.{{cite journal |last1=Dunn |first1=F. S. |last2=Kenchington |first2=C. G. |last3=Parry |first3=L. A. |last4=Clark |first4=J. W. |last5=Kendall |first5=R. S. |last6=Wilby |first6=P. R. |title=A crown-group cnidarian from the Ediacaran of Charnwood Forest, UK |journal=Nature Ecology & Evolution |date=25 July 2022 |volume=6 |issue=8 |pages=1095–1104 |doi=10.1038/s41559-022-01807-x |pmid=35879540 |pmc=9349040 |bibcode=2022NatEE...6.1095D}}

Some palaeontologists have suggested that animals appeared much earlier than the Cambrian explosion, possibly as early as 1 billion years ago.{{cite book |last1=Campbell |first1=Neil A. |last2=Reece |first2=Jane B. |title=Biology |year=2005 |publisher=Pearson, Benjamin Cummings |isbn=978-0-8053-7171-0 |edition=7th |page=526}} Early fossils that might represent animals appear for example in the 665-million-year-old rocks of the Trezona Formation of South Australia. These fossils are interpreted as most probably being early sponges.{{cite journal |title=Possible animal-body fossils in pre-Marinoan limestones from South Australia |journal=Nature Geoscience |volume=3 |pages=653–659 |date=17 August 2010 |doi=10.1038/ngeo934 |issue=9 |bibcode=2010NatGe...3..653M |last1=Maloof |first1=Adam C. |last2=Rose |first2=Catherine V. |last3=Beach |first3=Robert |last4=Samuels |first4=Bradley M. |last5=Calmet |first5=Claire C. |last6=Erwin |first6=Douglas H. |last7=Poirier |first7=Gerald R. |last8=Yao |first8=Nan |last9=Simons |first9=Frederik J.}}

Trace fossils such as tracks and burrows found in the Tonian period (from 1 gya) may indicate the presence of triploblastic worm-like animals, roughly as large (about 5 mm wide) and complex as earthworms.{{cite journal |last1=Seilacher |first1=Adolf |author1-link=Adolf Seilacher |last2=Bose |first2=Pradip K. |last3=Pfluger |first3=Friedrich |title=Triploblastic animals more than 1 billion years ago: trace fossil evidence from india |journal=Science |volume=282 |pages=80–83 |date=2 October 1998 |doi=10.1126/science.282.5386.80 |pmid=9756480 |issue=5386 |bibcode=1998Sci...282...80S}} However, similar tracks are produced by the giant single-celled protist Gromia sphaerica, so the Tonian trace fossils may not indicate early animal evolution.{{cite journal |last1=Matz |first1=Mikhail V. |last2=Frank |first2=Tamara M. |last3=Marshall |first3=N. Justin |last4=Widder |first4=Edith A. |last5=Johnsen |first5=Sönke |title=Giant Deep-Sea Protist Produces Bilaterian-like Traces |journal=Current Biology |volume=18 |issue=23 |pages=1849–54 |date=9 December 2008 |doi=10.1016/j.cub.2008.10.028 |pmid=19026540 |s2cid=8819675 |doi-access=free |bibcode=2008CBio...18.1849M}}{{cite news |last=Reilly |first=Michael |title=Single-celled giant upends early evolution |newspaper=NBC News |date=20 November 2008 |url=https://www.nbcnews.com/id/wbna27827279 |access-date=5 December 2008 |archive-url=https://web.archive.org/web/20130329062924/https://www.nbcnews.com/id/27827279/ |archive-date=29 March 2013 |url-status=live}} Around the same time, the layered mats of microorganisms called stromatolites decreased in diversity, perhaps due to grazing by newly evolved animals.{{Cite encyclopedia |last=Bengtson |first=S. |year=2002 |chapter=Origins and early evolution of predation |encyclopedia=The Paleontological Society Papers |volume=8 |title=The fossil record of predation |editor-last=Kowalewski |editor-first=M. |editor-last2=Kelley |editor-first2=P. H. |pages=289–317 |publisher=The Paleontological Society |chapter-url=https://www.nrm.se/download/18.4e32c81078a8d9249800021552/Bengtson2002predation.pdf |access-date=3 March 2018 |archive-date=30 October 2019 |archive-url=https://web.archive.org/web/20191030140248/https://www.nrm.se/download/18.4e32c81078a8d9249800021552/Bengtson2002predation.pdf |url-status=live}} Objects such as sediment-filled tubes that resemble trace fossils of the burrows of wormlike animals have been found in 1.2 gya rocks in North America, in 1.5 gya rocks in Australia and North America, and in 1.7 gya rocks in Australia. Their interpretation as having an animal origin is disputed, as they might be water-escape or other structures.{{cite book |last=Seilacher |first=Adolf |author-link=Adolf Seilacher |title=Trace fossil analysis |date=2007 |publisher=Springer |isbn=978-3-540-47226-1 |publication-place=Berlin |pages=176–177 |oclc=191467085}}{{cite journal |last=Breyer |first=J. A. |year=1995 |title=Possible new evidence for the origin of metazoans prior to 1 Ga: Sediment-filled tubes from the Mesoproterozoic Allamoore Formation, Trans-Pecos Texas |journal=Geology |volume=23 |issue=3 |pages=269–272 |doi=10.1130/0091-7613(1995)023<0269:PNEFTO>2.3.CO;2 |bibcode=1995Geo....23..269B}}

File:DickinsoniaCostata.jpg|Dickinsonia costata from the Ediacaran biota (c. 635–542 mya) is one of the earliest animal species known.{{cite journal |last1=Bobrovskiy |first1=Ilya |last2=Hope |first2=Janet M. |last3=Ivantsov |first3=Andrey |last4=Nettersheim |first4=Benjamin J. |last5=Hallmann |first5=Christian |last6=Brocks |first6=Jochen J. |title=Ancient steroids establish the Ediacaran fossil Dickinsonia as one of the earliest animals |journal=Science |volume=361 |issue=6408 |date=20 September 2018 |doi=10.1126/science.aat7228 |pmid=30237355 |pages=1246–1249 |bibcode=2018Sci...361.1246B |doi-access=free}}

File:Auroralumina attenboroughii reconstruction.jpg|Auroralumina attenboroughii, an Ediacaran predator (c. 560 mya)

File:20191203 Anomalocaris canadensis.png|Anomalocaris canadensis is one of the many animal species that emerged in the Cambrian explosion, starting some 539 mya, and found in the fossil beds of the Burgess shale.

{{further|Lists of animals}}

Animals are monophyletic, meaning they are derived from a common ancestor. Animals are the sister group to the choanoflagellates, with which they form the Choanozoa.{{cite journal |doi=10.1111/brv.12239 |pmid=26588818 |title=The origin of the animals and a 'Savannah' hypothesis for early bilaterian evolution |journal=Biological Reviews |volume=92 |issue=1 |pages=446–473 |year=2017 |last1=Budd |first1=Graham E. |last2=Jensen |first2=Sören |doi-access=free}}

Ros-Rocher and colleagues (2021) trace the origins of animals to unicellular ancestors, providing the external phylogeny shown in the cladogram. Uncertainty of relationships is indicated with dashed lines. The animal clade had certainly originated by 650 mya, and may have come into being as much as 800 mya, based on molecular clock evidence for different phyla.{{cite journal |last1=Ros-Rocher |first1=Núria |last2=Pérez-Posada |first2=Alberto |last3=Leger |first3=Michelle M. |last4=Ruiz-Trillo |first4=Iñaki |title=The origin of animals: an ancestral reconstruction of the unicellular-to-multicellular transition |journal=Open Biology |publisher=The Royal Society |volume=11 |issue=2 |year=2021 |page=200359 |doi=10.1098/rsob.200359 |pmid=33622103 |pmc=8061703}}

{{Clade |style=font-size:100%; line-height:100%

|label1=Opisthokonta |sublabel1=

|1={{Clade

|1=Holomycota (inc. fungi) 60 px

|label2=Holozoa |sublabel2=

|2={{Clade |state=dashed

|1=Ichthyosporea 50 px

|2=Pluriformea 50 px

|label3=Filozoa

|3={{Clade

|1=Filasterea 60 px

|label2=Choanozoa |sublabel2=

|2={{Clade

|label1=Choanoflagellatea |1=60 px

|label2 =Animalia |sublabel2=over 650 mya |2= 60 px

}}

}}

}}

}}

}}

{{anchor|basal}}

The relationships at the base of the animal tree have been debated.{{Cite journal |last1=Erives |first1=Albert |last2=Fritzsch |first2=Bernd |date=2019-07-17 |title=A screen for gene paralogies delineating evolutionary branching order of early Metazoa |url=https://www.biorxiv.org/content/10.1101/704551v1 |journal=bioRxiv |pages=704551 |doi=10.1101/704551 |doi-access=free}}{{cite journal |last1=Kapli |first1=Paschalia |last2=Telford |first2=Maximilian J. |title=Topology-dependent asymmetry in systematic errors affects phylogenetic placement of Ctenophora and Xenacoelomorpha |journal=Science Advances |date=11 December 2020 |volume=6 |issue=10 |pages=eabc5162 |doi=10.1126/sciadv.abc5162 |pmid=33310849 |pmc=7732190 |bibcode=2020SciA....6.5162K |doi-access=free}} Other than Ctenophora, the Bilateria and Cnidaria are the only groups with symmetry, and other evidence shows they are closely related.{{cite book |last1=Giribet |first1=G. |last2=Edgecombe |first2=G.D. |title=The Invertebrate Tree of Life |year=2020 |publisher=Princeton University Press |url={{GBurl |id=YHetDwAAQBAJ |p=21}} |page=21 |isbn=978-0-6911-7025-1 |access-date=27 May 2023}} In addition to sponges, Placozoa has no symmetry and was often considered a "missing link" between protists and multicellular animals. The presence of hox genes in Placozoa shows that they were once more complex.{{cite journal |last=Wanninger |first=Andreas |date=2024 |title=Hox, homology, and parsimony: An organismal perspective |journal=Seminars in Cell & Developmental Biology |volume=152-153 |pages=16–23 |doi=10.1016/j.semcdb.2023.01.007 |doi-access=free |pmid=36670036 }}

The Porifera (sponges) have long been assumed to be sister to the rest of the animals, but there is evidence that the Ctenophora may be in that position. Molecular phylogenetics has supported both the sponge-sister and ctenophore-sister hypotheses. In 2017, Roberto Feuda and colleagues, using amino acid differences, presented both, with the following cladogram for the sponge-sister view that they supported (their ctenophore-sister tree simply interchanging the places of ctenophores and sponges):{{Cite journal |last1=Feuda |first1=Roberto |last2=Dohrmann |first2=Martin |last3=Pett |first3=Walker |last4=Philippe |first4=Hervé |last5=Rota-Stabelli |first5=Omar |last6=Lartillot |first6=Nicolas |last7=Wörheide |first7=Gert |last8=Pisani |first8=Davide |display-authors=5 |title=Improved Modeling of Compositional Heterogeneity Supports Sponges as Sister to All Other Animals |journal=Current Biology |volume=27 |issue=24 |pages=3864–3870.e4 |doi=10.1016/j.cub.2017.11.008 |pmid=29199080 |year=2017 |doi-access=free |bibcode=2017CBio...27E3864F |hdl=10449/43929 |hdl-access=free}}

{{clade |style = font-size:100%; line-height:100%

|label1=Animalia |sublabel1=multicellular

|1={{clade

|1=Porifera 50 px

|label2=Eumetazoa

|2={{clade

|1=Ctenophora 60 px

|label2=ParaHoxozoa |sublabel2=hox genes

|2={{clade

|1=Placozoa 60 px

|sublabel2=symmetry

|2={{clade

|1=Cnidaria 70px

|2=Bilateria 50 px

}}

}}

}}

}}

}}

Conversely, a 2023 study by Darrin Schultz and colleagues uses ancient gene linkages to construct the following ctenophore-sister phylogeny:{{Cite journal |last1=Schultz |first1=Darrin T. |last2=Haddock |first2=Steven H. D. |author2-link=Steven Haddock |last3=Bredeson |first3=Jessen V. |last4=Green |first4=Richard E. |last5=Simakov |first5=Oleg |last6=Rokhsar |first6=Daniel S. |date=2023-05-17 |title=Ancient gene linkages support ctenophores as sister to other animals |url=https://rdcu.be/dcJSY |journal=Nature |volume=618 |issue=7963 |pages=110–117 |doi=10.1038/s41586-023-05936-6 |pmid=37198475 |pmc=10232365 |bibcode=2023Natur.618..110S}}

{{clade |style = font-size:100%; line-height:100%

|label1=Animalia |sublabel1=multicellular

|1={{clade

|1=Ctenophora 60 px

|label2=Myriazoa

|2={{clade

|1=Porifera 50 px

|label2=ParaHoxozoa |sublabel2=hox genes

|2={{clade

|1={{clade

|1=Placozoa 60 px

|2=Cnidaria 70px

}}

|label2= |sublabel2=symmetry

|2=Bilateria 50 px

}}

}}

}}

}}

File:Elephant-ear-sponge.jpg

Sponges are physically very distinct from other animals, and were long thought to have diverged first, representing the oldest animal phylum and forming a sister clade to all other animals.{{cite book |last1=Bhamrah |first1=H. S. |last2=Juneja |first2=Kavita |title=An Introduction to Porifera |year=2003 |publisher=Anmol Publications |isbn=978-81-261-0675-2 |page=58}} Despite their morphological dissimilarity with all other animals, genetic evidence suggests sponges may be more closely related to other animals than the comb jellies are.{{Cite journal |last1=Schultz |first1=Darrin T. |last2=Haddock |first2=Steven H. D. |last3=Bredeson |first3=Jessen V. |last4=Green |first4=Richard E. |last5=Simakov |first5=Oleg |last6=Rokhsar |first6=Daniel S. |date=17 May 2023 |title=Ancient gene linkages support ctenophores as sister to other animals |url=https://rdcu.be/dcJSY |journal=Nature |volume=618 |issue=7963 |pages=110–117 |doi=10.1038/s41586-023-05936-6 |pmid=37198475 |s2cid=258765122 |pmc=10232365 |bibcode=2023Natur.618..110S}}{{Cite journal |last1=Whelan |first1=Nathan V. |last2=Kocot |first2=Kevin M. |last3=Moroz |first3=Tatiana P. |last4=Mukherjee |first4=Krishanu |last5=Williams |first5=Peter |last6=Paulay |first6=Gustav |last7=Moroz |first7=Leonid L. |last8=Halanych |first8=Kenneth M. |display-authors=5 |date=9 October 2017 |title=Ctenophore relationships and their placement as the sister group to all other animals |url=https://rdcu.be/dcJS3 |journal=Nature Ecology & Evolution |volume=1 |issue=11 |pages=1737–1746 |doi=10.1038/s41559-017-0331-3 |pmid=28993654 |pmc=5664179 |bibcode=2017NatEE...1.1737W}} Sponges lack the complex organisation found in most other animal phyla;{{cite book |last=Sumich |first=James L. |title=Laboratory and Field Investigations in Marine Life |year=2008 |publisher=Jones & Bartlett Learning |isbn=978-0-7637-5730-4 |page=67}} their cells are differentiated, but in most cases not organised into distinct tissues, unlike all other animals.{{cite book |last=Jessop |first=Nancy Meyer |title=Biosphere; a study of life |year=1970 |publisher=Prentice-Hall |page=428}} They typically feed by drawing in water through pores, filtering out small particles of food.{{cite book |last=Sharma |first=N. S. |title=Continuity And Evolution Of Animals |year=2005 |publisher=Mittal Publications |isbn=978-81-8293-018-6 |page=106}}

The Ctenophora and Cnidaria are radially symmetric and have digestive chambers with a single opening, which serves as both mouth and anus.{{cite book |title=A Living Bay: The Underwater World of Monterey Bay |year=2000 |publisher=University of California Press |isbn=978-0-520-22149-9 |last1=Langstroth |first1=Lovell |last2=Langstroth |first2=Libby |editor-last=Newberry |editor-first=Todd |page=[https://archive.org/details/livingbayunderwa0000lang/page/244 244] |url=https://archive.org/details/livingbayunderwa0000lang/page/244}} Animals in both phyla have distinct tissues, but these are not organised into discrete organs.{{cite book |last=Safra |first=Jacob E. |title=The New Encyclopædia Britannica |volume=16 |year=2003 |publisher=Encyclopædia Britannica |isbn=978-0-85229-961-6 |page=523}} They are diploblastic, having only two main germ layers, ectoderm and endoderm.{{cite book |last=Kotpal |first=R.L. |title=Modern Text Book of Zoology: Invertebrates |publisher=Rastogi Publications |isbn=978-81-7133-903-7 |page=184 |year=2012}}

The tiny placozoans have no permanent digestive chamber and no symmetry; they superficially resemble amoebae.{{cite book |last=Barnes |first=Robert D. |year=1982 |title=Invertebrate Zoology |publisher=Holt-Saunders International |pages=84–85 |isbn=978-0-03-056747-6}}{{cite web |author= |title=Introduction to Placozoa |url=https://www.ucmp.berkeley.edu/phyla/placozoa/placozoa.html |publisher=UCMP Berkeley |access-date=10 March 2018 |archive-url=https://web.archive.org/web/20180325202849/https://www.ucmp.berkeley.edu/phyla/placozoa/placozoa.html |archive-date=25 March 2018 |url-status=live}} Their phylogeny is poorly defined, and under active research.{{Cite journal |last1=Srivastava |first1=Mansi |last2=Begovic |first2=Emina |last3=Chapman |first3=Jarrod |last4=Putnam |first4=Nicholas H. |last5=Hellsten |first5=Uffe |last6=Kawashima |first6=Takeshi |last7=Kuo |first7=Alan |last8=Mitros |first8=Therese |last9=Salamov |first9=Asaf |last10=Carpenter |first10=Meredith L. |last11=Signorovitch |first11=Ana Y. |last12=Moreno |first12=Maria A. |last13=Kamm |first13=Kai |last14=Grimwood |first14=Jane |last15=Schmutz |first15=Jeremy |display-authors=5 |date=1 August 2008 |title=The Trichoplax genome and the nature of placozoans |journal=Nature |volume=454 |issue=7207 |pages=955–960 |doi=10.1038/nature07191 |pmid=18719581 |bibcode=2008Natur.454..955S |s2cid=4415492 |doi-access=free}}

{{main|Bilateria|Symmetry (biology)#Bilateral symmetry}}

The remaining animals, the great majority—comprising some 29 phyla and over a million species—form the Bilateria clade, which have a bilaterally symmetric body plan. The Bilateria are triploblastic, with three well-developed germ layers, and their tissues form distinct organs. The digestive chamber has two openings, a mouth and an anus, and in the Nephrozoa there is an internal body cavity, a coelom or pseudocoelom. These animals have a head end (anterior) and a tail end (posterior), a back (dorsal) surface and a belly (ventral) surface, and a left and a right side. A modern consensus phylogenetic tree for the Bilateria is shown below.{{cite journal |last1=Dunn |first1=Casey W. |last2=Giribet |first2=Gonzalo |last3=Edgecombe |first3=Gregory D. |last4=Hejnol |first4=Andreas |title=Animal Phylogeny and Its Evolutionary Implications |journal=Annual Review of Ecology, Evolution, and Systematics |volume=45 |issue=1 |date=23 November 2014 |doi=10.1146/annurev-ecolsys-120213-091627 |pages=371–395}}

{{clade |style=font-size:85%;line-height:85%

|label1=Bilateria

|1={{clade

|1=Xenacoelomorpha 70 px

|label2= Nephrozoa

|sublabel2=650 Mya

|2={{clade

|label1=Deuterostomia

|1={{clade

|1=Ambulacraria 60 px

|2=Chordata 60 px

}}

|label2= Protostomia

|sublabel2=610 mya

|2={{clade

|1=Ecdysozoa 60 px

|2=Spiralia 60 px

}}

}}

}}

}}

File:Bilaterian body plan.svgn body plan.{{efn|Compare :File:Annelid redone w white background.svg for a more specific and detailed model of a particular phylum with this general body plan.}} With an elongated body and a direction of movement the animal has head and tail ends. Sense organs and mouth form the basis of the head. Opposed circular and longitudinal muscles enable peristaltic motion.]]

Having a front end means that this part of the body encounters stimuli, such as food, favouring cephalisation, the development of a head with sense organs and a mouth. Many bilaterians have a combination of circular muscles that constrict the body, making it longer, and an opposing set of longitudinal muscles, that shorten the body; these enable soft-bodied animals with a hydrostatic skeleton to move by peristalsis.{{cite journal |last=Quillin |first=K. J. |title=Ontogenetic scaling of hydrostatic skeletons: geometric, static stress and dynamic stress scaling of the earthworm lumbricus terrestris |journal=Journal of Experimental Biology |volume=201 |issue=12 |pages=1871–1883 |date=May 1998 |doi=10.1242/jeb.201.12.1871 |pmid=9600869 |url=https://jeb.biologists.org/cgi/pmidlookup?view=long&pmid=9600869 |doi-access=free |bibcode=1998JExpB.201.1871Q |access-date=4 March 2018 |archive-date=17 June 2020 |archive-url=https://web.archive.org/web/20200617135617/https://jeb.biologists.org/content/201/12/1871.long |url-status=live}} They also have a gut that extends through the basically cylindrical body from mouth to anus. Many bilaterian phyla have primary larvae which swim with cilia and have an apical organ containing sensory cells. However, over evolutionary time, descendant spaces have evolved which have lost one or more of each of these characteristics. For example, adult echinoderms are radially symmetric (unlike their larvae), while some parasitic worms have extremely simplified body structures.{{cite book |last=Minelli |first=Alessandro |title=Perspectives in Animal Phylogeny and Evolution |url={{GBurl |id=jIASDAAAQBAJ |p=53}} |year=2009 |publisher=Oxford University Press |isbn=978-0-19-856620-5 |page=53}}{{Cite book |url=https://www.sinauer.com/media/wysiwyg/samples/Brusca3e_Chapter_9.pdf |chapter=Introduction to the Bilateria and the Phylum Xenacoelomorpha {{!}} Triploblasty and Bilateral Symmetry Provide New Avenues for Animal Radiation |title=Invertebrates |last=Brusca |first=Richard C. |date=2016 |publisher=Sinauer Associates |pages=345–372 |isbn=978-1-60535-375-3 |access-date=4 March 2018 |archive-url=https://web.archive.org/web/20190424155137/https://www.sinauer.com/media/wysiwyg/samples/Brusca3e_Chapter_9.pdf |archive-date=24 April 2019 |url-status=live}}

Genetic studies have considerably changed zoologists' understanding of the relationships within the Bilateria. Most appear to belong to two major lineages, the protostomes and the deuterostomes.{{cite journal |last=Telford |first=Maximilian J. |title=Resolving Animal Phylogeny: A Sledgehammer for a Tough Nut? |journal=Developmental Cell |volume=14 |issue=4 |year=2008 |doi=10.1016/j.devcel.2008.03.016 |pages=457–459 |pmid=18410719 |doi-access=free}} It is often suggested that the basalmost bilaterians are the Xenacoelomorpha, with all other bilaterians belonging to the subclade Nephrozoa.{{cite journal |last1=Philippe |first1=H. |last2=Brinkmann |first2=H. |last3=Copley |first3=R. R. |last4=Moroz |first4=L. L. |last5=Nakano |first5=H. |last6=Poustka |first6=A. J. |last7=Wallberg |first7=A. |last8=Peterson |first8=K. J. |last9=Telford |first9=M. J. |title=Acoelomorph flatworms are deuterostomes related to Xenoturbella |journal=Nature |volume=470 |pages=255–258 |year=2011 |pmid=21307940 |doi=10.1038/nature09676 |bibcode=2011Natur.470..255P |issue=7333 |pmc=4025995}}{{cite journal |last1=Perseke |first1=M. |last2=Hankeln |first2=T. |last3=Weich |first3=B. |last4=Fritzsch |first4=G. |last5=Stadler |first5=P. F. |last6=Israelsson |first6=O. |last7=Bernhard |first7=D. |last8=Schlegel |first8=M. |title=The mitochondrial DNA of Xenoturbella bocki: genomic architecture and phylogenetic analysis |journal=Theory Biosci |volume=126 |issue=1 |date=August 2007 |pages=35–42 |url=https://www.bioinf.uni-leipzig.de/Publications/PREPRINTS/07-009.pdf |pmid=18087755 |doi=10.1007/s12064-007-0007-7 |citeseerx=10.1.1.177.8060 |s2cid=17065867 |access-date=4 March 2018 |archive-url=https://web.archive.org/web/20190424154927/https://www.bioinf.uni-leipzig.de/Publications/PREPRINTS/07-009.pdf |archive-date=24 April 2019 |url-status=live}}{{cite journal |last1=Cannon |first1=Johanna T. |last2=Vellutini |first2=Bruno C. |last3=Smith III |first3=Julian. |last4=Ronquist |first4=Frederik |last5=Jondelius |first5=Ulf |last6=Hejnol |first6=Andreas |date=3 February 2016 |title=Xenacoelomorpha is the sister group to Nephrozoa |journal=Nature |volume=530 |issue=7588 |pages=89–93 |doi=10.1038/nature16520 |pmid=26842059 |bibcode=2016Natur.530...89C |s2cid=205247296 |url=https://urn.kb.se/resolve?urn=urn:nbn:se:nrm:diva-1844 |access-date=21 February 2022 |archive-date=30 July 2022 |archive-url=https://web.archive.org/web/20220730091447/http://nrm.diva-portal.org/smash/record.jsf?pid=diva2%3A1037430&dswid=-7165 |url-status=live}} However, this suggestion has been contested, with other studies finding that xenacoelomorphs are more closely related to Ambulacraria than to other bilaterians.{{Cite journal |last1=Kapli |first1=Paschalia |last2=Natsidis |first2=Paschalis |last3=Leite |first3=Daniel J. |last4=Fursman |first4=Maximilian |last5=Jeffrie |first5=Nadia |last6=Rahman |first6=Imran A. |last7=Philippe |first7=Hervé |last8=Copley |first8=Richard R. |last9=Telford |first9=Maximilian J. |date=19 March 2021 |title=Lack of support for Deuterostomia prompts reinterpretation of the first Bilateria |journal=Science Advances |volume=7 |issue=12 |pages=eabe2741 |doi=10.1126/sciadv.abe2741 |pmc=7978419 |pmid=33741592 |bibcode=2021SciA....7.2741K}}

{{clear}}

{{further|Embryological origins of the mouth and anus}}

{{main|Protostome|Deuterostome}}

File:Protovsdeuterostomes.svgs, the blastopore develops into the mouth, while in deuterostomes it becomes the anus.]]

Protostomes and deuterostomes differ in several ways. Early in development, deuterostome embryos undergo radial cleavage during cell division, while many protostomes (the Spiralia) undergo spiral cleavage.{{cite journal |last=Valentine |first=James W. |date=July 1997 |title=Cleavage patterns and the topology of the metazoan tree of life |journal=PNAS |volume=94 |pages=8001–8005 |bibcode=1997PNAS...94.8001V |doi=10.1073/pnas.94.15.8001 |pmid=9223303 |pmc=21545 |issue=15 |doi-access=free}}

Animals from both groups possess a complete digestive tract, but in protostomes the first opening of the embryonic gut develops into the mouth, and the anus forms secondarily. In deuterostomes, the anus forms first while the mouth develops secondarily.{{cite book |last1=Peters |first1=Kenneth E. |last2=Walters |first2=Clifford C. |last3=Moldowan |first3=J. Michael |title=The Biomarker Guide: Biomarkers and isotopes in petroleum systems and Earth history |volume=2 |year=2005 |publisher=Cambridge University Press |isbn=978-0-521-83762-0 |page=717}}{{cite book |last1=Hejnol |first1=A. |last2=Martindale |first2=M. Q. |url=https://www.researchgate.net/publication/230766195 |chapter=The mouth, the anus, and the blastopore – open questions about questionable openings |title=Animal Evolution – Genomes, Fossils, and Trees |editor-last1=Telford |editor-first1=M. J. |editor-last2=Littlewood |editor-first2=D. J. |year=2009 |publisher=Oxford University Press |isbn=978-0-19-957030-0 |pages=33–40 |access-date=1 March 2018 |archive-url=https://web.archive.org/web/20181028190247/https://www.researchgate.net/publication/230766195 |archive-date=28 October 2018 |url-status=live}} Most protostomes have schizocoelous development, where cells simply fill in the interior of the gastrula to form the mesoderm. In deuterostomes, the mesoderm forms by enterocoelic pouching, through invagination of the endoderm.{{cite book |last=Safra |first=Jacob E. |title=The New Encyclopædia Britannica, Volume 1; Volume 3 |year=2003 |publisher=Encyclopædia Britannica |isbn=978-0-85229-961-6 |page=767}}

The main deuterostome phyla are the Ambulacraria and the Chordata.{{cite book |last=Hyde |first=Kenneth |title=Zoology: An Inside View of Animals |year=2004 |publisher=Kendall Hunt |isbn=978-0-7575-0997-1 |page=345}} Ambulacraria are exclusively marine and include acorn worms, starfish, sea urchins, and sea cucumbers.{{cite book |last=Alcamo |first=Edward |title=Biology Coloring Workbook |year=1998 |publisher=The Princeton Review |isbn=978-0-679-77884-4 |page=220}} The chordates are dominated by the vertebrates (animals with backbones),{{cite book |last=Holmes |first=Thom |title=The First Vertebrates |publisher=Infobase |year=2008 |isbn=978-0-8160-5958-4 |page=64}} which consist of fishes, amphibians, reptiles, birds, and mammals.{{cite book |last=Rice |first=Stanley A. |title=Encyclopedia of evolution |publisher=Infobase |year=2007 |page=[https://archive.org/details/encyclopediaofev0000rice/page/75 75] |isbn=978-0-8160-5515-9 |url=https://archive.org/details/encyclopediaofev0000rice/page/75}}{{cite book |last1=Tobin |first1=Allan J. |last2=Dusheck |first2=Jennie |title=Asking about life |year=2005 |publisher=Cengage |isbn=978-0-534-40653-0 |page=497}}{{cite journal |title=Hemichordate genomes and deuterostome origins |journal=Nature |date=26 November 2015 |pages=459–465 |volume=527 |issue=7579 |doi=10.1038/nature16150 |first1=Oleg |last1=Simakov |first2=Takeshi |last2=Kawashima |first3=Ferdinand |last3=Marlétaz |first4=Jerry |last4=Jenkins |first5=Ryo |last5=Koyanagi |first6=Therese |last6=Mitros |first7=Kanako |last7=Hisata |first8=Jessen |last8=Bredeson |first9=Eiichi |last9=Shoguchi |display-authors=5 |pmid=26580012 |pmc=4729200 |bibcode=2015Natur.527..459S}}

File:Spiral cleavage in Trochus.png develop with spiral cleavage in the embryo, as here in a sea snail.]]

The protostomes include the Ecdysozoa, named after their shared trait of ecdysis, growth by moulting,{{cite book |last=Dawkins |first=Richard |author-link=Richard Dawkins |title=The Ancestor's Tale: A Pilgrimage to the Dawn of Evolution |year=2005 |publisher=Houghton Mifflin Harcourt |isbn=978-0-618-61916-0 |page=[https://archive.org/details/ancestorstale00rich_0/page/381 381] |url=https://archive.org/details/ancestorstale00rich_0/page/381}} Among the largest ecdysozoan phyla are the arthropods and the nematodes.{{cite book |last1=Prewitt |first1=Nancy L. |last2=Underwood |first2=Larry S. |last3=Surver |first3=William |title=BioInquiry: making connections in biology |year=2003 |publisher=John Wiley |isbn=978-0-471-20228-8 |page=[https://archive.org/details/bioinquiry00nanc_0/page/289 289] |url=https://archive.org/details/bioinquiry00nanc_0/page/289}} The rest of the protostomes are in the Spiralia, named for their pattern of developing by spiral cleavage in the early embryo. Major spiralian phyla include the annelids and molluscs.{{cite journal |pmid=10781038 |pmc=34316 |jstor=122407 |bibcode=2000PNAS...97.4434S |doi=10.1073/pnas.97.9.4434 |title=Evolution of the bilaterian body plan: What have we learned from annelids? |journal=Proceedings of the National Academy of Sciences |volume=97 |issue=9 |pages=4434–4437 |year=2000 |last1=Shankland |first1=M. |last2=Seaver |first2=E.C. |doi-access=free}}

{{further|Taxonomy (biology)|History of zoology through 1859|History of zoology since 1859}}

File:Jean-Baptiste de Lamarck.jpg led the creation of a modern classification of invertebrates, breaking up Linnaeus's "Vermes" into 9 phyla by 1809.]]

In the classical era, Aristotle divided animals,{{efn|In his History of Animals and Parts of Animals.}} based on his own observations, into those with blood (roughly, the vertebrates) and those without. The animals were then arranged on a scale from man (with blood, two legs, rational soul) down through the live-bearing tetrapods (with blood, four legs, sensitive soul) and other groups such as crustaceans (no blood, many legs, sensitive soul) down to spontaneously generating creatures like sponges (no blood, no legs, vegetable soul). Aristotle was uncertain whether sponges were animals, which in his system ought to have sensation, appetite, and locomotion, or plants, which did not: he knew that sponges could sense touch and would contract if about to be pulled off their rocks, but that they were rooted like plants and never moved about.{{cite book |last=Leroi |first=Armand Marie |author-link=Armand Marie Leroi |title=The Lagoon: How Aristotle Invented Science |title-link=Aristotle's Lagoon |publisher=Bloomsbury |date=2014 |isbn=978-1-4088-3622-4 |pages=111–119, 270–271}}

In 1758, Carl Linnaeus created the first hierarchical classification in his Systema Naturae.{{cite book |last=Linnaeus |first=Carl |author-link=Carl Linnaeus |title=Systema naturae per regna tria naturae :secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. |edition=10th |publisher=Holmiae (Laurentii Salvii) |year=1758 |url=https://www.biodiversitylibrary.org/bibliography/542 |access-date=22 September 2008 |language=la |trans-title=The System of Nature through the Three Kingdoms of Nature |archive-url=https://web.archive.org/web/20081010032456/https://www.biodiversitylibrary.org/bibliography/542 |archive-date=10 October 2008 |url-status=live}} In his original scheme, the animals were one of three kingdoms, divided into the classes of Vermes, Insecta, Pisces, Amphibia, Aves, and Mammalia. Since then, the last four have all been subsumed into a single phylum, the Chordata, while his Insecta (which included the crustaceans and arachnids) and Vermes have been renamed or broken up. The process was begun in 1793 by Jean-Baptiste de Lamarck, who called the Vermes {{lang|fr|une espèce de chaos}} ('a chaotic mess'){{efn|The French prefix {{lang|fr|une espèce de}} is pejorative.{{cite dictionary |title=Espèce de |url=https://dictionnaire.reverso.net/francais-anglais/esp%C3%A8ce%20de%20cr%C3%A9tin |dictionary=Reverso dictionnnaire |access-date=1 March 2018 |archive-url=https://web.archive.org/web/20130728151210/https://dictionnaire.reverso.net/francais-anglais/esp%C3%A8ce%20de%20cr%C3%A9tin |archive-date=28 July 2013 |url-status=live |language=fr,en}}}} and split the group into three new phyla: worms, echinoderms, and polyps (which contained corals and jellyfish). By 1809, in his Philosophie Zoologique, Lamarck had created nine phyla apart from vertebrates (where he still had four phyla: mammals, birds, reptiles, and fish) and molluscs, namely cirripedes, annelids, crustaceans, arachnids, insects, worms, radiates, polyps, and infusorians.{{cite book |last=Gould |first=Stephen Jay |author-link=Stephen Jay Gould |title=The Lying Stones of Marrakech |url={{GBurl |id=wApMpVmi-5gC |p=130}} |year=2011 |publisher=Harvard University Press |isbn=978-0-674-06167-5 |pages=130–134}}

In his 1817 {{lang|fr|Le Règne Animal}}, Georges Cuvier used comparative anatomy to group the animals into four {{lang|fr|embranchements}} ('branches' with different body plans, roughly corresponding to phyla), namely vertebrates, molluscs, articulated animals (arthropods and annelids), and zoophytes (radiata) (echinoderms, cnidaria and other forms).{{cite book |last=de Wit |first=Hendrik C. D. |title=Histoire du développement de la biologie |volume=III |publisher=Presses polytechniques et universitaires Romandes |year=1994 |pages=94–96 |isbn=978-2-88074-264-5 |language=fr}} This division into four was followed by the embryologist Karl Ernst von Baer in 1828, the zoologist Louis Agassiz in 1857, and the comparative anatomist Richard Owen in 1860.

In 1874, Ernst Haeckel divided the animal kingdom into two subkingdoms: Metazoa (multicellular animals, with five phyla: coelenterates, echinoderms, articulates, molluscs, and vertebrates) and Protozoa (single-celled animals), including a sixth animal phylum, sponges.{{cite book |last1=Haeckel |first1=Ernst |author-link=Ernst Haeckel |title=Anthropogenie oder Entwickelungsgeschichte des menschen |url=https://archive.org/details/anthropogenieod05haecgoog |year=1874 |page=202 |language=de |trans-title=Anthropogeny or the Development story of Humans |publisher=W. Engelmann}}{{cite book |last=Valentine |first=James W. |title=On the Origin of Phyla |url={{GBurl |id=DMBkmHm5fe4C |p=8}} |year=2004 |publisher=University of Chicago Press |isbn=978-0-226-84548-7 |pages=7–8}} The protozoa were later moved to the former kingdom Protista, leaving only the Metazoa as a synonym of Animalia.{{cite book |last1=Hutchins |first1=Michael |title=Grzimek's Animal Life Encyclopedia |url=https://archive.org/details/animallifeprotos02mich_714 |url-access=limited |year=2003 |edition=2nd |publisher=Gale |isbn=978-0-7876-5777-2 |page=[https://archive.org/details/animallifeprotos02mich_714/page/n21 3]}}

{{main|Human uses of animals}}

File:Carni bovine macellate.JPG in a slaughterhouse]]

The human population exploits a large number of other animal species for food, both of domesticated livestock species in animal husbandry and, mainly at sea, by hunting wild species.{{cite web |url=https://www.fao.org/fishery/ |title=Fisheries and Aquaculture |publisher=Food and Agriculture Organization |access-date=8 July 2016 |archive-url=https://web.archive.org/web/20090519173740/https://www.fao.org/fishery |archive-date=19 May 2009 |url-status=live}} Marine fish of many species are caught commercially for food. A smaller number of species are farmed commercially.{{cite book |last=Helfman |first=Gene S. |title=Fish Conservation: A Guide to Understanding and Restoring Global Aquatic Biodiversity and Fishery Resources |url=https://archive.org/details/fishconservation00helf |url-access=limited |date=2007 |publisher=Island |isbn=978-1-59726-760-1 |page=[https://archive.org/details/fishconservation00helf/page/n25 11]}}{{cite web |title=World Review of Fisheries and Aquaculture |url=https://www.fao.org/docrep/016/i2727e/i2727e01.pdf |publisher=FAO |access-date=13 August 2015 |archive-url=https://web.archive.org/web/20150828131307/https://www.fao.org/docrep/016/i2727e/i2727e01.pdf |archive-date=28 August 2015 |url-status=live}} Humans and their livestock make up more than 90% of the biomass of all terrestrial vertebrates, and almost as much as all insects combined.{{cite journal |last=Eggleton |first=Paul |title=The State of the World's Insects |journal=Annual Review of Environment and Resources |date=17 October 2020 |volume=45 |issue=1 |pages=61–82 |doi=10.1146/annurev-environ-012420-050035 |doi-access=free}}

Invertebrates including cephalopods, crustaceans, insects—principally bees and silkworms—and bivalve or gastropod molluscs are hunted or farmed for food, fibres.{{cite journal |title=Shellfish climbs up the popularity ladder |journal=Seafood Business |url=https://www.highbeam.com/doc/1G1-85675992.html |archive-url=https://web.archive.org/web/20121105143157/https://www.highbeam.com/doc/1G1-85675992.html |url-status=dead |archive-date=5 November 2012 |access-date=8 July 2016 |date=January 2002}}{{Cite encyclopedia |date=2024-09-17 |title=Western honeybee |encyclopedia=Encyclopædia Britannica |url=https://www.britannica.com/animal/western-honeybee |access-date=2024-10-20}} Chickens, cattle, sheep, pigs, and other animals are raised as livestock for meat across the world.{{cite news |title=Graphic detail Charts, maps and infographics. Counting chickens |newspaper=The Economist |url=https://www.economist.com/blogs/dailychart/2011/07/global-livestock-counts |access-date=23 June 2016 |date=27 July 2011 |archive-url=https://web.archive.org/web/20160715181213/https://www.economist.com/blogs/dailychart/2011/07/global-livestock-counts |archive-date=15 July 2016 |url-status=live}}{{cite web |url=https://cattle-today.com/ |title=Breeds of Cattle at Cattle Today |publisher=Cattle-today.com |access-date=15 October 2013 |archive-url=https://web.archive.org/web/20110715234745/https://cattle-today.com/ |archive-date=15 July 2011 |url-status=live}}{{cite web |last1=Lukefahr |first1=S. D. |last2=Cheeke |first2=P. R. |title=Rabbit project development strategies in subsistence farming systems |url=https://www.fao.org/docrep/U4900T/u4900T0m.htm |publisher=Food and Agriculture Organization |access-date=23 June 2016 |archive-url=https://web.archive.org/web/20160506105314/https://www.fao.org/docrep/U4900T/u4900T0m.htm |archive-date=6 May 2016 |url-status=live}} Animal fibres such as wool and silk are used to make textiles, while animal sinews have been used as lashings and bindings, and leather is widely used to make shoes and other items. Animals have been hunted and farmed for their fur to make items such as coats and hats.{{cite web |title=Ancient fabrics, high-tech geotextiles |url=https://www.naturalfibres2009.org/en/fibres/ |publisher=Natural Fibres |access-date=8 July 2016 |archive-url=https://web.archive.org/web/20160720093749/https://www.naturalfibres2009.org/en/fibres/ |archive-date=20 July 2016 |url-status=dead}} Dyestuffs including carmine (cochineal),{{cite book |url=https://www.fao.org/docrep/v8879e/v8879e09.htm |chapter=Cochineal and Carmine |title=Major colourants and dyestuffs, mainly produced in horticultural systems |publisher=FAO |access-date=16 June 2015 |archive-url=https://web.archive.org/web/20180306060330/https://www.fao.org/docrep/v8879e/V8879e09.htm |archive-date=6 March 2018 |url-status=live}}{{cite web |url=https://www.fda.gov/ForIndustry/ColorAdditives/GuidanceComplianceRegulatoryInformation/ucm153038.htm |title=Guidance for Industry: Cochineal Extract and Carmine |publisher=FDA |access-date=6 July 2016 |archive-url=https://web.archive.org/web/20160713100106/https://www.fda.gov/ForIndustry/ColorAdditives/GuidanceComplianceRegulatoryInformation/ucm153038.htm |archive-date=13 July 2016 |url-status=live}} shellac,{{cite news |title=How Shellac Is Manufactured |url=https://nla.gov.au/nla.news-article55073762 |access-date=17 July 2015 |newspaper=The Mail |location=Adelaide |date=18 December 1937 |archive-date=30 July 2022 |archive-url=https://web.archive.org/web/20220730091433/https://trove.nla.gov.au/newspaper/article/55073762 |url-status=live}}{{cite journal |last1=Pearnchob |first1=N. |last2=Siepmann |first2=J. |last3=Bodmeier |first3=R. |year=2003 |title=Pharmaceutical applications of shellac: moisture-protective and taste-masking coatings and extended-release matrix tablets |journal=Drug Development and Industrial Pharmacy |volume=29 |issue=8 |pages=925–938 |pmid=14570313 |doi=10.1081/ddc-120024188 |s2cid=13150932}} and kermes{{cite book |last=Barber |first=E. J. W. |title=Prehistoric Textiles |year=1991 |publisher=Princeton University Press |isbn=978-0-691-00224-8 |pages=230–231}}{{cite book |last=Munro |first=John H. |title=The Cambridge History of Western Textiles |chapter=Medieval Woollens: Textiles, Technology, and Organisation |editor-last1=Jenkins |editor-first1=David |year=2003 |publisher=Cambridge University Press |isbn=978-0-521-34107-3 |pages=214–215}} have been made from the bodies of insects. Working animals including cattle and horses have been used for work and transport from the first days of agriculture.{{cite book |last=Pond |first=Wilson G. |title=Encyclopedia of Animal Science |url={{GBurl |id=1SQl7Ao3mHoC |p=248}} |year=2004 |publisher=CRC Press |isbn=978-0-8247-5496-9 |pages=248–250 |access-date=22 February 2018}}

Animals such as the fruit fly Drosophila melanogaster serve a major role in science as experimental models.{{cite web |title=Genetics Research |url=https://www.aht.org.uk/cms-display/genetics.html |publisher=Animal Health Trust |access-date=24 June 2016 |archive-url=https://web.archive.org/web/20171212193051/https://www.aht.org.uk/cms-display/genetics.html |archive-date=12 December 2017 |url-status=dead}}{{cite web |title=Drug Development |url=https://www.animalresearch.info/en/drug-development/ |publisher=Animal Research.info |access-date=24 June 2016 |archive-url=https://web.archive.org/web/20160608124406/https://www.animalresearch.info/en/drug-development/ |archive-date=8 June 2016 |url-status=live}}{{cite web |title=Animal Experimentation |url=https://www.bbc.co.uk/ethics/animals/using/experiments_1.shtml |publisher=BBC |access-date=8 July 2016 |archive-url=https://web.archive.org/web/20160701220536/https://www.bbc.co.uk/ethics/animals/using/experiments_1.shtml |archive-date=1 July 2016 |url-status=live}}{{cite web |title=EU statistics show decline in animal research numbers |url=https://speakingofresearch.com/2013/12/12/eu-statistics-show-decline-in-animal-research-numbers/ |publisher=Speaking of Research |year=2013 |access-date=24 January 2016 |archive-url=https://web.archive.org/web/20171006162448/https://speakingofresearch.com/2013/12/12/eu-statistics-show-decline-in-animal-research-numbers/ |archive-date=6 October 2017 |url-status=live}} Animals have been used to create vaccines since their discovery in the 18th century.{{cite web |title=Vaccines and animal cell technology |date=10 June 2013 |url=https://www.actip.org/library/vaccines-and-animal-cell-technology/ |publisher=Animal Cell Technology Industrial Platform |access-date=9 July 2016 |archive-url=https://web.archive.org/web/20160713184805/https://www.actip.org/library/vaccines-and-animal-cell-technology/ |archive-date=13 July 2016 |url-status=live}} Some medicines such as the cancer drug trabectedin are based on toxins or other molecules of animal origin.{{cite web |title=Medicines by Design |url=https://publications.nigms.nih.gov/medbydesign/chapter3.html |publisher=National Institute of Health |access-date=9 July 2016 |archive-url=https://web.archive.org/web/20160604214644/https://publications.nigms.nih.gov/medbydesign/chapter3.html |archive-date=4 June 2016 |url-status=live}}

File:Hebbuz.JPG retrieving a duck during a hunt]]

People have used hunting dogs to help chase down and retrieve animals,{{cite book |last=Fergus |first=Charles |title=Gun Dog Breeds, A Guide to Spaniels, Retrievers, and Pointing Dogs |publisher=The Lyons Press |date=2002 |isbn=978-1-58574-618-7}} and birds of prey to catch birds and mammals,{{cite web |title=History of Falconry |url=https://www.thefalconrycentre.co.uk/bird-info/conservation/nocturnal-raptors/history-falconry/ |publisher=The Falconry Centre |access-date=22 April 2016 |archive-url=https://web.archive.org/web/20160529023926/https://thefalconrycentre.co.uk/bird-info/conservation/nocturnal-raptors/history-falconry/ |archive-date=29 May 2016 |url-status=live}} while tethered cormorants have been used to catch fish.{{cite book |last=King |first=Richard J. |title=The Devil's Cormorant: A Natural History |url={{GBurl |id=ucGyAAAAQBAJ |p=9}} |date=2013 |publisher=University of New Hampshire Press |isbn=978-1-61168-225-0 |page=9}} Poison dart frogs have been used to poison the tips of blowpipe darts.{{cite web |url=https://amphibiaweb.org/lists/Dendrobatidae.shtml |title=Dendrobatidae |publisher=AmphibiaWeb |access-date=10 October 2008 |archive-url=https://web.archive.org/web/20110810090554/https://amphibiaweb.org/lists/Dendrobatidae.shtml |archive-date=10 August 2011 |url-status=live}}{{cite web |url=https://animaldiversity.ummz.umich.edu/site/accounts/information/Dendrobatidae.html |title=Dendrobatidae |access-date=9 July 2016 |last=Heying |first=H. |year=2003 |publisher=Animal Diversity Web |archive-url=https://web.archive.org/web/20110212005358/https://animaldiversity.ummz.umich.edu/site/accounts/information/Dendrobatidae.html |archive-date=12 February 2011 |url-status=live}}

A wide variety of animals are kept as pets, from invertebrates such as tarantulas, octopuses, and praying mantises,{{cite web |title=Other bugs |date=18 February 2011 |url=https://www.keepinginsects.com/cockroaches-locusts-ants/ |publisher=Keeping Insects |access-date=8 July 2016 |archive-url=https://web.archive.org/web/20160707170022/https://www.keepinginsects.com/cockroaches-locusts-ants/ |archive-date=7 July 2016 |url-status=live}} reptiles such as snakes and chameleons,{{cite web |last=Kaplan |first=Melissa |title=So, you think you want a reptile? |url=https://www.anapsid.org/parent.html |publisher=Anapsid.org |access-date=8 July 2016 |archive-url=https://web.archive.org/web/20160703115141/https://www.anapsid.org/parent.html |archive-date=3 July 2016 |url-status=live}} and birds including canaries, parakeets, and parrots{{cite web |title=Pet Birds |url=https://www.humanesociety.org/animals/pet_birds/ |publisher=PDSA |access-date=8 July 2016 |archive-url=https://web.archive.org/web/20160707053516/https://www.humanesociety.org/animals/pet_birds/ |archive-date=7 July 2016 |url-status=live}} all finding a place. However, the most kept pet species are mammals, namely dogs, cats, and rabbits.{{cite web |url=https://www.shea-online.org/Portals/0/PDFs/Animals%20in%20Healthcare%20Facilities.pdf |title=Animals in Healthcare Facilities |year=2012 |url-status=dead |archive-url=https://web.archive.org/web/20160304102728/https://www.shea-online.org/Portals/0/PDFs/Animals%20in%20Healthcare%20Facilities.pdf |archive-date=4 March 2016}}{{cite web |last=The Humane Society of the United States |title=U.S. Pet Ownership Statistics |url=https://www.humanesociety.org/issues/pet_overpopulation/facts/pet_ownership_statistics.html |access-date=27 April 2012 |archive-url=https://web.archive.org/web/20120407193941/https://www.humanesociety.org/issues/pet_overpopulation/facts/pet_ownership_statistics.html |archive-date=7 April 2012 |url-status=live}}{{cite web |title=U.S. Rabbit Industry profile |publisher=United States Department of Agriculture |url=https://www.aphis.usda.gov/animal_health/emergingissues/downloads/RabbitReport1.pdf |access-date=10 July 2013 |url-status=dead |archive-url=https://web.archive.org/web/20131020161216/https://www.aphis.usda.gov/animal_health/emergingissues/downloads/RabbitReport1.pdf |archive-date=20 October 2013}} There is a tension between the role of animals as companions to humans, and their existence as individuals with rights of their own.{{cite journal |last=Plous |first=S. |title=The Role of Animals in Human Society |date=1993 |doi=10.1111/j.1540-4560.1993.tb00906.x |journal=Journal of Social Issues |volume=49 |issue=1 |pages=1–9}}

A wide variety of terrestrial and aquatic animals are hunted for sport.{{cite book |last=Hummel |first=Richard |title=Hunting and Fishing for Sport: Commerce, Controversy, Popular Culture |date=1994 |publisher=Popular Press |isbn=978-0-87972-646-1 |url-access=registration |url=https://archive.org/details/huntingfishingfo0000humm}}

The signs of the Western and Chinese zodiacs are based on animals.{{cite book |last=Lau |first=Theodora |title=The Handbook of Chinese Horoscopes |pages=2–8, 30–35, 60–64, 88–94, 118–124, 148–153, 178–184, 208–213, 238–244, 270–278, 306–312, 338–344 |publisher=Souvenir |year=2005}}{{cite book |last=Tester |first=S. Jim |title=A History of Western Astrology |url={{GBurl |id=L0HSvH96alIC |p=31}} |year=1987 |publisher=Boydell & Brewer |isbn=978-0-85115-446-6 |pages=31–33 and passim}} In China and Japan, the butterfly has been seen as the personification of a person's soul,{{cite book |last=Hearn |first=Lafcadio |author-link=Lafcadio Hearn |year=1904 |title=Kwaidan: Stories and Studies of Strange Things |title-link=Kwaidan: Stories and Studies of Strange Things |publisher=Dover |isbn=978-0-486-21901-1}} and in classical representation the butterfly is also the symbol of the soul.{{Cite journal |url=https://quod.lib.umich.edu/cgi/t/text/text-idx?c=did;cc=did;rgn=main;view=text;idno=did2222.0001.694 |title=Butterfly |journal=Encyclopedia of Diderot and d'Alembert |access-date=16 December 2023 |date=January 2011 |first=Louis |last=De Jaucourt |archive-url=https://web.archive.org/web/20160811042437/https://quod.lib.umich.edu/cgi/t/text/text-idx?c=did;cc=did;rgn=main;view=text;idno=did2222.0001.694 |archive-date=11 August 2016 |url-status=live}}Hutchins, M., Arthur V. Evans, Rosser W. Garrison and Neil Schlager (Eds) (2003), Grzimek's Animal Life Encyclopedia, 2nd edition. Volume 3, Insects. Gale, 2003.

File:Alexander Coosemans - Still Life with Lobster and Oysters.jpg with Lobster and Oysters by Alexander Coosemans, {{Circa|1660}}]]

Animals have been the subjects of art from the earliest times, both historical, as in ancient Egypt, and prehistoric, as in the cave paintings at Lascaux. Major animal paintings include Albrecht Dürer's 1515 The Rhinoceros, and George Stubbs's {{Circa|1762}} horse portrait Whistlejacket.{{cite news |last1=Jones |first1=Jonathan |title=The top 10 animal portraits in art |url=https://www.theguardian.com/artanddesign/jonathanjonesblog/2014/jun/27/top-10-animal-portraits-in-art |access-date=24 June 2016 |newspaper=The Guardian |date=27 June 2014 |archive-url=https://web.archive.org/web/20160518105922/https://www.theguardian.com/artanddesign/jonathanjonesblog/2014/jun/27/top-10-animal-portraits-in-art |archive-date=18 May 2016 |url-status=live}} Insects, birds and mammals play roles in literature and film,{{Cite journal |last1=Paterson |first1=Jennifer |title=Animals in Film and Media |url=https://www.oxfordbibliographies.com/view/document/obo-9780199791286/obo-9780199791286-0044.xml |journal=Oxford Bibliographies |access-date=24 June 2016 |date=29 October 2013 |doi=10.1093/obo/9780199791286-0044 |archive-url=https://web.archive.org/web/20160614200642/https://www.oxfordbibliographies.com/view/document/obo-9780199791286/obo-9780199791286-0044.xml |archive-date=14 June 2016 |url-status=live}} such as in giant bug movies.{{cite book |last1=Gregersdotter |first1=Katarina |last2=Höglund |first2=Johan |last3=Hållén |first3=Nicklas |title=Animal Horror Cinema: Genre, History and Criticism |url={{GBurl |id=hV-hCwAAQBAJ |p=147}} |date=2016 |publisher=Springer |isbn=978-1-137-49639-3 |page=147}}{{cite book |last1=Warren |first1=Bill |last2=Thomas |first2=Bill |title=Keep Watching the Skies!: American Science Fiction Movies of the Fifties, The 21st Century Edition |url={{GBurl |id=B7kUCwAAQBAJ |pg=PT32}} |date=2009 |publisher=McFarland & Company |isbn=978-1-4766-2505-8 |page=32}}{{cite book |last=Crouse |first=Richard |title=Son of the 100 Best Movies You've Never Seen |url={{GBurl |id=B5alnowvF3sC |pg=PT200}} |year=2008 |publisher=ECW Press |isbn=978-1-55490-330-6 |page=200}}

Animals including insects and mammals feature in mythology and religion. The scarab beetle was sacred in ancient Egypt,{{cite book |last=Ben-Tor |first=Daphna |title=Scarabs, A Reflection of Ancient Egypt |location=Jerusalem |publisher=Israel Museum |date=1989 |isbn=978-965-278-083-6 |page=8}} and the cow is sacred in Hinduism.{{Cite news |last=Biswas |first=Soutik |title=Why the humble cow is India's most polarising animal |url=https://www.bbc.co.uk/news/world-asia-india-34513185 |publisher=BBC |access-date=9 July 2016 |date=15 October 2015 |archive-url=https://web.archive.org/web/20161122205058/https://www.bbc.co.uk/news/world-asia-india-34513185 |archive-date=22 November 2016 |url-status=live}} Among other mammals, deer,{{cite web |title=Deer |url=https://treesforlife.org.uk/forest/mythology-folklore/deer/ |publisher=Trees for Life |access-date=23 June 2016 |archive-url=https://web.archive.org/web/20160614200842/https://treesforlife.org.uk/forest/mythology-folklore/deer/ |archive-date=14 June 2016 |url-status=live}} horses,{{cite book |title=Hayagrīva: The Mantrayānic Aspect of Horse-cult in China and Japan |publisher=Brill Archive |page=9 |last=van Gulik |first=Robert Hans}} lions,{{cite web |last1=Grainger |first1=Richard |title=Lion Depiction across Ancient and Modern Religions |url=https://lionalert.org/page/Lion_Depiction_Across_Ancient_and_Modern_Religions |publisher=Alert |access-date=6 July 2016 |date=24 June 2012 |url-status=dead |archive-url=https://web.archive.org/web/20160923134807/https://lionalert.org/page/Lion_Depiction_Across_Ancient_and_Modern_Religions |archive-date=23 September 2016}} bats,{{cite book |last1=Read |first1=Kay Almere |last2=Gonzalez |first2=Jason J. |year=2000 |title=Mesoamerican Mythology |publisher=Oxford University Press |pages=132–134}} bears,{{Cite journal |last=Wunn |first=Ina |s2cid=53595088 |date=January 2000 |title=Beginning of Religion |journal=Numen |volume=47 |issue=4 |pages=417–452 |doi=10.1163/156852700511612}} and wolves{{cite book |last=McCone |first=Kim R. |title=Studien zum indogermanischen Wortschatz |publisher=Institut für Sprachwissenschaft der Universität Innsbruck |year=1987 |editor-last=Meid |editor-first=W. |location=Innsbruck |pages=101–154 |language=de |chapter=Hund, Wolf, und Krieger bei den Indogermanen}} are the subjects of myths and worship.

• Animal coloration
• Ethology
• Lists of organisms by population
• World Animal Day, observed on 4 October

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• [https://tolweb.org/ Tree of Life Project]. {{Webarchive|url=https://web.archive.org/web/20110612121424/http://www.tolweb.org//|date=12 June 2011}}
• [https://animaldiversity.org/ Animal Diversity Web] – University of Michigan's database of animals
• [https://archive.today/20160426231847/https://www.arkive.org/ Wildscreen Arkive] – multimedia database of endangered/protected species

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{{Life on Earth}}

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Animals

Animals

Category:Cryogenian first appearances

Category:Taxa named by Carl Linnaeus

Category:Biology terminology