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84-605: One of its popular events is the penguin parade, which is performed daily after noon if the outside temperature is below ten degrees Celsius. The zoologist Heini Hediger was director of the Zurich Zoo from 1954 to 1973. The current director is Severin Dressen. The zoo is member of WAZA and the EAZA . The most famous attractions are the Asian elephant exhibit and Masoala Hall, which are inside of

168-399: A gastrula with a digestive chamber and two separate germ layers , an external ectoderm and an internal endoderm . In most cases, a third germ layer, the mesoderm , also develops between them. These germ layers then differentiate to form tissues and organs. Repeated instances of mating with a close relative during sexual reproduction generally leads to inbreeding depression within

252-770: A clade Xenambulacraria for the Xenacoelamorpha + Ambulacraria; this is either within Deuterostomia, as sister to Chordata, or the Deuterostomia are recovered as paraphyletic, and Xenambulacraria is sister to the proposed clade Centroneuralia , consisting of Chordata + Protostomia. Several animal phyla lack bilateral symmetry. These are the Porifera (sea sponges), Placozoa , Cnidaria (which includes jellyfish , sea anemones , and corals), and Ctenophora (comb jellies). Sponges are physically very distinct from other animals, and were long thought to have diverged first, representing

336-468: 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. 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

420-658: A hollow sphere of cells, the blastula , during embryonic development . Animals form a clade , meaning that they arose from a single common ancestor . Over 1.5 million living animal species have been described , of which around 1.05 million are insects , over 85,000 are molluscs , and around 65,000 are vertebrates . It has been estimated there are as many as 7.77 million animal species on Earth. Animal body lengths range from 8.5 μm (0.00033 in) to 33.6 m (110 ft). They have complex ecologies and interactions with each other and their environments, forming intricate food webs . The scientific study of animals

504-601: A laboratory setting. Ethologists have been particularly concerned with the evolution of behavior and the understanding of behavior in terms of the theory of natural selection . In one sense, the first modern ethologist was Charles Darwin , whose book, The Expression of the Emotions in Man and Animals , influenced many future ethologists. A subfield of ethology is behavioral ecology which attempts to answer Nikolaas Tinbergen 's four questions with regard to animal behavior: what are

588-498: A large dome. Guests can even view elephants from underwater. They are also known as the only and first European institution to successfully breed Galápagos tortoises . Over the course of the years, the Zurich attraction has sent the baby tortoises to more than two dozen other zoos. In 2005 the zoo discovered that the seven lemurs caught in Andasibe thought to be mouse lemurs were actually

672-413: A new footing, by explaining the processes by which it can occur, and providing observational evidence that it had done so. Darwin's theory was rapidly accepted by the scientific community and soon became a central axiom of the rapidly developing science of biology. The basis for modern genetics began with the work of Gregor Mendel on peas in 1865, although the significance of his work was not realized at

756-406: A new perspective on the fundamental basis of life. Having previously been the realm of gentlemen naturalists, over the 18th, 19th and 20th centuries, zoology became an increasingly professional scientific discipline . Explorer-naturalists such as Alexander von Humboldt investigated the interaction between organisms and their environment, and the ways this relationship depends on geography, laying

840-449: A new species later named Goodman mouse lemur. The zoo made international headlines in July 2020 when a Siberian tiger mauled a zookeeper to death in front of members of the public. In 1992 a new plan for the development of the zoo was presented. The area of the zoo was to be doubled by 2020, while keeping the number of species the same and redoing most of the enclosures. The goal was to shift

924-1105: A population due to the increased prevalence of harmful recessive traits. Animals have evolved numerous mechanisms for avoiding close inbreeding . 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 . 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 , and parasites . Interactions between animals of each biome form complex food webs within that ecosystem . In carnivorous or omnivorous species, predation

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1008-709: A process involving the union of a male and female haploid gamete , each gamete formed by meiosis . Ordinarily, gametes produced by separate individuals unite by a process of fertilization to form a diploid zygote that can then develop into a genetically unique individual progeny. However, some animals are also capable, as an alternative reproductive process, to reproduce parthenogenetically. Parthenogenesis has been described in snakes and lizards (see Misplaced Pages Parthenogenesis in squamates ), in amphibians (see Misplaced Pages Parthenogenesis in amphibians ) and in numerous other species (see Misplaced Pages Parthenogenesis ). Generally, meiosis in parthanogenetically reproducing animals occurs by

1092-518: A similar process to that in sexually reproducing animals, but the diploid zygote nucleus is generated by the union of two haploid genomes from the same individual rather than from different individuals. Animal Animals are multicellular , eukaryotic organisms in the biological kingdom Animalia ( / ˌ æ n ɪ ˈ m eɪ l i ə / ). With few exceptions, animals consume organic material , breathe oxygen , have myocytes and are able to move , can reproduce sexually , and grow from

1176-439: A single opening, which serves as both mouth and anus. Animals in both phyla have distinct tissues, but these are not organised into discrete organs . They are diploblastic , having only two main germ layers, ectoderm and endoderm. The tiny placozoans have no permanent digestive chamber and no symmetry; they superficially resemble amoebae. Their phylogeny is poorly defined, and under active research. The remaining animals,

1260-464: Is a consumer–resource interaction where the predator feeds on another organism, its prey , 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 . Almost all multicellular predators are animals. Some consumers use multiple methods; for example, in parasitoid wasps ,

1344-453: Is a form of scientific taxonomy . Modern biological classification has its root in the work of Carl Linnaeus , who grouped species according to shared physical characteristics. These groupings have since been revised to improve consistency with the Darwinian principle of common descent . Molecular phylogenetics , which uses nucleic acid sequence as data, has driven many recent revisions and

1428-433: Is a stage in embryonic development that is unique to animals, allowing cells to be differentiated into specialised tissues and organs. All animals are composed of cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins . During development, the animal extracellular matrix forms a relatively flexible framework upon which cells can move about and be reorganised, making

1512-657: Is administered by the International Code of Zoological Nomenclature . A merging draft, BioCode, was published in 1997 in an attempt to standardize nomenclature, but has yet to be formally adopted. Vertebrate zoology is the biological discipline that consists of the study of vertebrate animals, that is animals with a backbone , such as fish , amphibians , reptiles , birds and mammals . The various taxonomically oriented disciplines i.e. mammalogy , biological anthropology , herpetology , ornithology , and ichthyology seek to identify and classify species and study

1596-480: Is an integrative field of study, uniting concepts and information from evolutionary biology , taxonomy , ecology , physical geography , geology , paleontology and climatology . The origin of this field of study is widely accredited to Alfred Russel Wallace , a British biologist who had some of his work jointly published with Charles Darwin . Molecular biology studies the common genetic and developmental mechanisms of animals and plants, attempting to answer

1680-402: Is being studied. For example, what is learned about the physiology of yeast cells can also apply to human cells. The field of animal physiology extends the tools and methods of human physiology to non-human species. Physiology studies how, for example, the nervous , immune , endocrine , respiratory , and circulatory systems function and interact. Developmental biology is the study of

1764-458: Is disputed, as they might be water-escape or other structures. 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 . The dates on the phylogenetic tree indicate approximately how many millions of years ago ( mya ) the lineages split. Ros-Rocher and colleagues (2021) trace

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1848-406: Is done on both the microscopic and molecular levels for single-celled organisms such as bacteria as well as the specialized cells in multicellular organisms such as humans . Understanding the structure and function of cells is fundamental to all of the biological sciences. The similarities and differences between cell types are particularly relevant to molecular biology. Anatomy considers

1932-414: Is known as zoology , and the study of animal behaviour is known as ethology . The animal kingdom is divided into five infrakingdoms / superphyla , namely Porifera , Ctenophora , Placozoa , Cnidaria and Bilateria . Most living animal species belong to the infrakingdom Bilateria, a highly proliferative clade whose members have a bilaterally symmetric and significantly cephalised body plan , and

2016-443: Is likely to continue to do so. Biological classification belongs to the science of zoological systematics . Many scientists now consider the five-kingdom system outdated. Modern alternative classification systems generally start with the three-domain system : Archaea (originally Archaebacteria); Bacteria (originally Eubacteria); Eukaryota (including protists , fungi , plants , and animals ) These domains reflect whether

2100-822: Is often used to refer only to nonhuman animals. The term metazoa is derived from Ancient Greek μετα meta 'after' (in biology, the prefix meta- stands for 'later') and ζῷᾰ zōia 'animals', plural of ζῷον zōion 'animal'. Animals have several characteristics that set them apart from other living things. Animals are eukaryotic and multicellular . Unlike plants and algae , which produce their own nutrients , animals are heterotrophic , feeding on organic material and digesting it internally. With very few exceptions, animals respire aerobically . All animals are motile (able to spontaneously move their bodies) during at least part of their life cycle , but some animals, such as sponges , corals , mussels , and barnacles , later become sessile . The blastula

2184-422: 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. The first body fossils of animals appear in

2268-415: Is partly based on paleontology , which uses the fossil record to answer questions about the mode and tempo of evolution, and partly on the developments in areas such as population genetics and evolutionary theory. Following the development of DNA fingerprinting techniques in the late 20th century, the application of these techniques in zoology has increased the understanding of animal populations. In

2352-406: Is quantitative, and recently a significant amount of work has been done using computer science techniques such as bioinformatics and computational biology . Molecular genetics , the study of gene structure and function, has been among the most prominent sub-fields of molecular biology since the early 2000s. Other branches of biology are informed by molecular biology, by either directly studying

2436-698: Is reflected in zoology by the presence of animals in Egyptian hieroglyphics. Although the concept of zoology as a single coherent field arose much later, the zoological sciences emerged from natural history reaching back to the biological works of Aristotle and Galen in the ancient Greco-Roman world . In the fourth century BC, Aristotle looked at animals as living organisms, studying their structure, development and vital phenomena. He divided them into two groups: animals with blood, equivalent to our concept of vertebrates , and animals without blood, invertebrates . He spent two years on Lesbos , observing and describing

2520-559: Is the genus, and sapiens the specific epithet, both of them combined make up the species name. When writing the scientific name of an organism, it is proper to capitalize the first letter in the genus and put all of the specific epithet in lowercase. Additionally, the entire term may be italicized or underlined. The dominant classification system is called the Linnaean taxonomy . It includes ranks and binomial nomenclature . The classification, taxonomy , and nomenclature of zoological organisms

2604-448: Is the scientific study of animals . Its studies include the structure , embryology , classification , habits , and distribution of all animals, both living and extinct , and how they interact with their ecosystems . Zoology is one of the primary branches of biology . The term is derived from Ancient Greek ζῷον , zōion ('animal'), and λόγος , logos ('knowledge', 'study'). Although humans have always been interested in

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2688-614: Is the subfield of biology that studies the evolutionary processes (natural selection, common descent, speciation) that produced the diversity of life on Earth. Evolutionary research is concerned with the origin and descent of species , as well as their change over time, and includes scientists from many taxonomically oriented disciplines. For example, it generally involves scientists who have special training in particular organisms such as mammalogy , ornithology , herpetology , or entomology , but use those organisms as systems to answer general questions about evolution. Evolutionary biology

2772-614: The Ediacaran , represented by forms such as Charnia and Spriggina . It had long been doubted whether these fossils truly represented animals, 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. Many animal phyla first appear in

2856-545: The anatomy of different groups. It is closely related to evolutionary biology and phylogeny (the evolution of species). Physiology studies the mechanical, physical, and biochemical processes of living organisms by attempting to understand how all of the structures function as a whole. The theme of "structure to function" is central to biology. Physiological studies have traditionally been divided into plant physiology and animal physiology , but some principles of physiology are universal, no matter what particular organism

2940-665: The evolutionary relationships between taxa . Humans make use of many other animal species for food (including meat , eggs , and dairy products ), for materials (such as leather , fur , and wool ), as pets and as working animals for transportation , and services . Dogs , the first domesticated animal, have been used in hunting , in security and in warfare , as have horses , pigeons and birds of prey ; while other terrestrial and aquatic animals are hunted for sports, trophies or profits. Non-human animals are also an important cultural element of human evolution , having appeared in cave arts and totems since

3024-518: The fossil record during the Cambrian explosion , starting about 539 million years ago, in beds such as the Burgess shale . 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

3108-497: The lobe-finned fish Tiktaalik started to move on to land in the late Devonian , about 375 million years ago. 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. Animals are however not particularly heat tolerant ; very few of them can survive at constant temperatures above 50 °C (122 °F) or in

3192-550: The proximate causes of the behavior, the developmental history of the organism, the survival value and phylogeny of the behavior? Another area of study is animal cognition , which uses laboratory experiments and carefully controlled field studies to investigate an animal's intelligence and learning. Biogeography studies the spatial distribution of organisms on the Earth , focusing on topics like dispersal and migration , plate tectonics , climate change , and cladistics . It

3276-399: The taxonomist . Originally it was thought that species were immutable, but with the arrival of Darwin's theory of evolution, the field of cladistics came into being, studying the relationships between the different groups or clades . Systematics is the study of the diversification of living forms, the evolutionary history of a group is known as its phylogeny , and the relationship between

3360-542: The 16th century. During the Renaissance and early modern period, zoological thought was revolutionized in Europe by a renewed interest in empiricism and the discovery of many novel organisms. Prominent in this movement were Andreas Vesalius and William Harvey , who used experimentation and careful observation in physiology , and naturalists such as Carl Linnaeus , Jean-Baptiste Lamarck , and Buffon who began to classify

3444-470: The 1980s, developmental biology re-entered evolutionary biology from its initial exclusion from the modern synthesis through the study of evolutionary developmental biology . Related fields often considered part of evolutionary biology are phylogenetics , systematics , and taxonomy . Ethology is the scientific and objective study of animal behavior under natural conditions, as opposed to behaviorism , which focuses on behavioral response studies in

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3528-698: The Cambrian explosion, possibly as early as 1 billion years ago. 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 . 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. However, similar tracks are produced by

3612-712: The Cnidaria) never grow larger than 20 μm , and one of the smallest species ( Myxobolus shekel ) is no more than 8.5 μm when fully grown. The following table lists estimated numbers of described extant species for the major animal phyla, along with their principal habitats (terrestrial, fresh water, and marine), and free-living or parasitic ways of life. 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

3696-449: The animals and plants, considering the adaptations of different organisms and the function of their parts. Four hundred years later, Roman physician Galen dissected animals to study their anatomy and the function of the different parts, because the dissection of human cadavers was prohibited at the time. This resulted in some of his conclusions being false, but for many centuries it was considered heretical to challenge any of his views, so

3780-427: The cells have nuclei or not, as well as differences in the chemical composition of the cell exteriors. Further, each kingdom is broken down recursively until each species is separately classified. The order is: Domain ; kingdom ; phylum ; class ; order ; family ; genus ; species . The scientific name of an organism is generated from its genus and species. For example, humans are listed as Homo sapiens . Homo

3864-434: The clades can be shown diagrammatically in a cladogram . Although someone who made a scientific study of animals would historically have described themselves as a zoologist, the term has come to refer to those who deal with individual animals, with others describing themselves more specifically as physiologists, ethologists, evolutionary biologists, ecologists, pharmacologists, endocrinologists or parasitologists. Although

3948-456: The dark sea floor consume organic matter produced through chemosynthesis (via oxidising inorganic compounds such as hydrogen sulfide ) by archaea and bacteria . 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 . Vertebrates such as

4032-514: The determination of the double helical structure of the DNA molecule by Francis Crick and James Watson in 1953, the realm of molecular biology opened up, leading to advances in cell biology , developmental biology and molecular genetics . The study of systematics was transformed as DNA sequencing elucidated the degrees of affinity between different organisms. Zoology is the branch of science dealing with animals . A species can be defined as

4116-643: The discovery of the structure of DNA by Francis Crick and James Watson in 1953, the realm of molecular biology opened up, leading to advances in cell biology , developmental biology and molecular genetics . The history of zoology traces the study of the animal kingdom from ancient to modern times. Prehistoric people needed to study the animals and plants in their environment to exploit them and survive. Cave paintings, engravings and sculptures in France dating back 15,000 years show bison, horses, and deer in carefully rendered detail. Similar images from other parts of

4200-456: The diversity of life and the fossil record , as well as studying the development and behavior of organisms. Antonie van Leeuwenhoek did pioneering work in microscopy and revealed the previously unknown world of microorganisms , laying the groundwork for cell theory . van Leeuwenhoek's observations were endorsed by Robert Hooke ; all living organisms were composed of one or more cells and could not generate spontaneously. Cell theory provided

4284-450: The earliest times, and are frequently featured in mythology , religion , arts , literature , heraldry , politics , and sports . The word animal comes from the Latin noun animal of the same meaning, which is itself derived from Latin animalis 'having breath or soul'. The biological definition includes all members of the kingdom Animalia. In colloquial usage, the term animal

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4368-565: The first hierarchical biological classification for animals in 1758 with his Systema Naturae , which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa (now synonymous with Animalia) and the Protozoa , single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics , which are effective at demonstrating

4452-504: The focus away from displaying animals towards displaying ecosystems, allowing animals to retreat into spaces hidden from visitors. To house these ecosystems - Eurasia, South America and Africa/Madagascar - the zoo was geographically divided into distinct zones. An updated master plan serves as guideline even recently: As of 2023: Zoologist Zoology ( UK : / z u ˈ ɒ l ə dʒ i / zoo- OL -ə-jee , US : / z oʊ ˈ ɒ l ə dʒ i / zoh- OL -ə-jee )

4536-448: The formation of complex structures possible. This may be calcified, forming structures such as shells , bones , and spicules . 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. Animal cells uniquely possess the cell junctions called tight junctions , gap junctions , and desmosomes . With few exceptions—in particular,

4620-404: The forms of macroscopic structures such as organs and organ systems. It focuses on how organs and organ systems work together in the bodies of humans and other animals, in addition to how they work independently. Anatomy and cell biology are two studies that are closely related, and can be categorized under "structural" studies. Comparative anatomy is the study of similarities and differences in

4704-600: The fossil record as marine species during the Cambrian explosion , which began around 539  million years ago (Mya), and most classes during the Ordovician radiation 485.4 Mya. 6,331 groups of genes common to all living animals have been identified; these may have arisen from a single common ancestor that lived about 650 Mya during the Cryogenian period. Historically, Aristotle divided animals into those with blood and those without . Carl Linnaeus created

4788-535: The fossil record in the late Cryogenian period and diversified in the subsequent Ediacaran period in what is known as the Avalon explosion . Earlier evidence of animals is still controversial; the sponge -like organism Otavia has been dated back to the Tonian period at the start of the Neoproterozoic , but its identity as an animal is heavily contested. Nearly all modern animal phyla became clearly established in

4872-520: The fossil record, rather than showing that all these animals appeared simultaneously. 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. Some palaeontologists have suggested that animals appeared much earlier than

4956-431: The foundations for biogeography , ecology and ethology . Naturalists began to reject essentialism and consider the importance of extinction and the mutability of species . These developments, as well as the results from embryology and paleontology , were synthesized in the 1859 publication of Charles Darwin 's theory of evolution by natural selection ; in this Darwin placed the theory of organic evolution on

5040-721: The giant single-celled protist Gromia sphaerica , so the Tonian trace fossils may not indicate early animal evolution. Around the same time, the layered mats of microorganisms called stromatolites decreased in diversity, perhaps due to grazing by newly evolved animals. 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

5124-461: 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 there is an internal body cavity, a coelom or pseudocoelom. These animals have

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5208-476: The interactions of molecules in their own right such as in cell biology and developmental biology , or indirectly, where molecular techniques are used to infer historical attributes of populations or species , as in fields in evolutionary biology such as population genetics and phylogenetics . There is also a long tradition of studying biomolecules "from the ground up", or molecularly, in biophysics . Animals generally reproduce by sexual reproduction ,

5292-404: The largest group of organisms in which any two individuals of the appropriate sex can produce fertile offspring; about 1.5 million species of animal have been described and it has been estimated that as many as 8 million animal species may exist. An early necessity was to identify the organisms and group them according to their characteristics, differences and relationships, and this is the field of

5376-441: The larvae feed on the hosts' living tissues, killing them in the process, but the adults primarily consume nectar from flowers. Other animals may have very specific feeding behaviours , such as hawksbill sea turtles which mainly eat sponges . Most animals rely on biomass and bioenergy produced by plants and phytoplanktons (collectively called producers ) through photosynthesis . Herbivores, as primary consumers , eat

5460-747: The most extreme cold deserts of continental Antarctica . The blue whale ( Balaenoptera musculus ) is the largest animal that has ever lived, weighing up to 190 tonnes and measuring up to 33.6 metres (110 ft) long. The largest extant terrestrial animal is the African bush elephant ( Loxodonta africana ), weighing up to 12.25 tonnes and measuring up to 10.67 metres (35.0 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. Several animals are microscopic; some Myxozoa ( obligate parasites within

5544-831: The natural history of the animals they saw around them, and used this knowledge to domesticate certain species, the formal study of zoology can be said to have originated with Aristotle . He viewed animals as living organisms, studied their structure and development, and considered their adaptations to their surroundings and the function of their parts. Modern zoology has its origins during the Renaissance and early modern period, with Carl Linnaeus , Antonie van Leeuwenhoek , Robert Hooke , Charles Darwin , Gregor Mendel and many others. The study of animals has largely moved on to deal with form and function, adaptations, relationships between groups, behaviour and ecology. Zoology has increasingly been subdivided into disciplines such as classification , physiology , biochemistry and evolution . With

5628-620: The oldest animal phylum and forming a sister clade to all other animals. 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. Sponges lack the complex organisation found in most other animal phyla; their cells are differentiated, but in most cases not organised into distinct tissues, unlike all other animals. They typically feed by drawing in water through pores, filtering out small particles of food. The comb jellies and Cnidaria are radially symmetric and have digestive chambers with

5712-528: The origins of animals to unicellular ancestors, providing the external phylogeny shown in the cladogram. Uncertainty of relationships is indicated with dashed lines. Holomycota (inc. fungi) [REDACTED] Ichthyosporea [REDACTED] Pluriformea [REDACTED] Filasterea [REDACTED] [REDACTED] [REDACTED] The most basal animals, the Porifera , Ctenophora , Cnidaria , and Placozoa , have body plans that lack bilateral symmetry . Their relationships have been disputed, as

5796-518: 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 . Some benthic animals living close to hydrothermal vents and cold seeps on

5880-517: The processes by which animals and plants reproduce and grow. The discipline includes the study of embryonic development , cellular differentiation , regeneration , asexual and sexual reproduction , metamorphosis , and the growth and differentiation of stem cells in the adult organism. Development of both animals and plants is further considered in the articles on evolution , population genetics , heredity , genetic variability , Mendelian inheritance , and reproduction . Evolutionary biology

5964-493: The questions regarding the mechanisms of genetic inheritance and the structure of the gene . In 1953, James Watson and Francis Crick described the structure of DNA and the interactions within the molecule, and this publication jump-started research into molecular biology and increased interest in the subject. While researchers practice techniques specific to molecular biology, it is common to combine these with methods from genetics and biochemistry . Much of molecular biology

6048-494: The results of his own investigations. His general approach was surprisingly modern, and he wrote, "For it is [the task] of natural science not simply to accept what we are told but to inquire into the causes of natural things." An early pioneer was Conrad Gessner , whose monumental 4,500-page encyclopedia of animals, Historia animalium , was published in four volumes between 1551 and 1558. In Europe, Galen's work on anatomy remained largely unsurpassed and unchallenged up until

6132-503: The rise of the germ theory of disease , though the mechanism of inheritance remained a mystery. In the early 20th century, the rediscovery of Mendel's work led to the rapid development of genetics , and by the 1930s the combination of population genetics and natural selection in the modern synthesis created evolutionary biology . Research in cell biology is interconnected to other fields such as genetics, biochemistry , medical microbiology , immunology , and cytochemistry . With

6216-1112: The sister group to all other animals could be the Porifera or the Ctenophora, both of which lack Hox genes , important for body plan development . Eumetazoa , a clade which contains Ctenophora and ParaHoxozoa , has been proposed as a sister group to Porifera . A competing hypothesis is the Benthozoa clade, which would consist of Porifera and ParaHoxozoa as a sister group of Ctenophora . In 2023, Darrin Schultz and colleagues studied ancient gene linkages to show that ctenophores are most likely sister to all other animals. Ctenophora [REDACTED] Porifera [REDACTED] Xenacoelomorpha [REDACTED] Ambulacraria [REDACTED] Chordata [REDACTED] Ecdysozoa [REDACTED] Spiralia [REDACTED] Placozoa [REDACTED] Cnidaria [REDACTED] A variant phylogeny, from Kapli and colleagues (2021), proposes

6300-407: The smaller, motile gametes are spermatozoa and the larger, non-motile gametes are ova . These fuse to form zygotes , 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. In most other groups, the blastula undergoes more complicated rearrangement. It first invaginates to form

6384-474: The sponges and placozoans —animal bodies are differentiated into tissues . These include muscles , which enable locomotion, and nerve tissues , which transmit signals and coordinate the body. Typically, there is also an internal digestive chamber with either one opening (in Ctenophora, Cnidaria, and flatworms) or two openings (in most bilaterians). Nearly all animals make use of some form of sexual reproduction. They produce haploid gametes by meiosis ;

6468-499: The structures and mechanisms specific to those groups. The rest of the animal kingdom is dealt with by invertebrate zoology , a vast and very diverse group of animals that includes sponges , echinoderms , tunicates , worms , molluscs , arthropods and many other phyla , but single-celled organisms or protists are not usually included. Cell biology studies the structural and physiological properties of cells , including their behavior , interactions, and environment . This

6552-529: The study of anatomy stultified. During the post-classical era , Middle Eastern science and medicine was the most advanced in the world, integrating concepts from Ancient Greece, Rome, Mesopotamia and Persia as well as the ancient Indian tradition of Ayurveda , while making numerous advances and innovations. In the 13th century, Albertus Magnus produced commentaries and paraphrases of all Aristotle's works; his books on topics like botany , zoology, and minerals included information from ancient sources, but also

6636-565: The study of animal life is ancient, its scientific incarnation is relatively modern. This mirrors the transition from natural history to biology at the start of the 19th century. Since Hunter and Cuvier , comparative anatomical study has been associated with morphography , shaping the modern areas of zoological investigation: anatomy , physiology , histology , embryology , teratology and ethology . Modern zoology first arose in German and British universities. In Britain, Thomas Henry Huxley

6720-433: The time. Darwin gave a new direction to morphology and physiology , by uniting them in a common biological theory: the theory of organic evolution. The result was a reconstruction of the classification of animals upon a genealogical basis, fresh investigation of the development of animals, and early attempts to determine their genetic relationships. The end of the 19th century saw the fall of spontaneous generation and

6804-467: The total number of nematode species include 10,000–20,000; 500,000; 10 million; and 100 million. 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. 3,000–6,500 4,000–25,000 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

6888-493: The vast majority of bilaterians belong to two large superphyla : the protostomes , which includes organisms such as arthropods , molluscs , flatworms , annelids and nematodes ; and the deuterostomes , which include echinoderms , hemichordates and chordates , the latter of which contains the vertebrates . The much smaller basal phylum Xenacoelomorpha have an uncertain position within Bilateria. Animals first appear in

6972-489: The world illustrated mostly the animals hunted for food and the savage animals. The Neolithic Revolution , which is characterized by the domestication of animals , continued throughout Antiquity. Ancient knowledge of wildlife is illustrated by the realistic depictions of wild and domestic animals in the Near East, Mesopotamia, and Egypt, including husbandry practices and techniques, hunting and fishing. The invention of writing

7056-502: Was a prominent figure. His ideas were centered on the morphology of animals. Many consider him the greatest comparative anatomist of the latter half of the 19th century. Similar to Hunter , his courses were composed of lectures and laboratory practical classes in contrast to the previous format of lectures only. Scientific classification in zoology , is a method by which zoologists group and categorize organisms by biological type , such as genus or species . Biological classification

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