Wallaby
A wallaby is a small- or mid-sized macropod native to Australia and New Guinea, with introduced populations in New Zealand, UK and other countries. They belong to the same taxonomic family as kangaroos and sometimes the same genus, but kangaroos are categorised into the six largest species of the family; the term wallaby is an informal designation used for any macropod, smaller than a kangaroo or wallaroo that has not been designated otherwise. There are 11 species of brush wallabies, their head and body length is 45 to 105 cm and the tail is 33 to 75 cm long. The six named species of rock-wallabies live among rocks near water; the two species of hare-wallabies are small animals that have the movements and some of the habits of hares. Called "pademelons", the three species of scrub wallabies of New Guinea, the Bismarck Archipelago, Tasmania are small and stocky, with short hind limbs and pointed noses. Wallabies are hunted for fur. A similar species is quokka; the three named species of forest wallabies are native to the island of New Guinea.
The dwarf wallaby is the smallest member of the genus and the smallest known member of the kangaroo family. Its length is about 46 cm from nose to tail, it weighs about 1.6 kg. The name wallaby comes from Dharug walabi or waliba. Young wallabies are known like many other marsupials. Adult male wallabies are referred to as "bucks", "boomers", or "jacks". An adult female wallaby is known as a "doe", "flyer", or "jill". A group of wallabies is called a "court", "mob", or "troupe". Forest-dwelling wallabies are known as "pademelons" and "dorcopsises". Although members of most wallaby species are small, some can grow up to two metres in length, their powerful hind legs are not only used for bounding at high speeds and jumping great heights, but to administer vigorous kicks to fend off potential predators. The Tammar wallaby has elastic storage in the ankle extensor tendons, without which the animal's metabolic rate might be 30–50% greater, it has been found that the design of spring-like tendon energy savings and economical muscle force generation is key for the two distal muscle–tendon units of the Tammar wallaby.
Wallabies have a powerful tail, used for balance and support. Wallabies are herbivores whose diet consists of a wide range of grasses, vegetables and other foliage. Due to recent urbanization, many wallabies now feed in urban areas. Wallabies cover vast distances for food and water, scarce in their environment. Mobs of wallabies congregate around the same water hole during the dry season. Wallabies face several threats. Wild dogs and feral cats are among their predators. Humans pose a significant threat to wallabies due to increased interaction. Many wallabies have been involved in vehicular accidents as they feed near roads and urban areas. Wallabies are not a distinct genetic group, they fall into several broad categories. Typical wallabies of the genus Macropus, like the agile wallaby, the red-necked wallaby are most related to the kangaroos and wallaroos and, size aside, look similar; these are the ones most seen in the southern states. Rock-wallabies, rather like the goats of the northern hemisphere, specialise in rugged terrain and have modified feet adapted to grip rock with skin friction rather than dig into soil with large claws.
There are at least fifteen species and the relationship between several of them is poorly understood. Several are endangered. Captive rock wallaby breeding programs like the one at Healesville Sanctuary have had some success and a small number have been released into the wild; the banded hare-wallaby is thought to be the last remaining member of the once-numerous subfamily Sthenurinae, although once common across southern Australia, is now restricted to two islands off the Western Australian coast which are free of introduced predators. It is not as related to the other hare wallabies as the hare wallabies are to the other wallabies. New Guinea, until recent geological times part of mainland Australia, has at least five species of wallaby. Wallabies are distributed across Australia in more remote timbered, or rugged areas, less so on the great semi-arid plains that are better suited to the larger and more fleet-footed kangaroos, they can be found on the island of New Guinea. Wallabies of several species have been introduced to other parts of the world, there are a number of breeding introduced populations, including: Kawau Island in New Zealand is home to large numbers of tammar, Parma and brush-tailed rock-wallaby from introductions made around 1870.
They are considered a pest on the island, but a programme to re-introduce them to Australia has met with only limited success. The Lake Tarawera area of New Zealand has a large tammar population; the South Canterbury district of New Zealand has a large population of Bennett's wallaby. On the Isle of Man in the Ballaugh Curraghs area, there is a population of over 100 red-necked wallabies, descended from a pair that escaped from the nearby Curraghs Wildlife Park in 1970. Hawaii has a small non-native populatio
Wombat
Wombats are short-legged, muscular quadrupedal marsupials that are native to Australia. They are about 1 m in length with stubby tails. There are three extant species and they are all members of the family Vombatidae, they are adaptable and habitat tolerant, are found in forested and heathland areas of south-eastern Australia, including Tasmania, as well as an isolated patch of about 300 ha in Epping Forest National Park in central Queensland. Though genetic studies of the Vombatidae have been undertaken, evolution of the family is not well understood. Wombats are estimated to have diverged from other Australian marsupials early, as long as 40 million years ago, while some estimates place divergence at around 25 million years. While some theories place wombats as miniaturised relatives of diprotodonts, such as the rhinoceros-sized Diprotodon, more recent studies place the Vombatiformes as having a distinct parallel evolution, hence their current classification as a separate family. Wombats dig extensive burrow systems with powerful claws.
One distinctive adaptation of wombats is their backward pouch. The advantage of a backward-facing pouch is that when digging, the wombat does not gather soil in its pouch over its young. Although crepuscular and nocturnal, wombats may venture out to feed on cool or overcast days, they are not seen, but leave ample evidence of their passage, treating fences as minor inconveniences to be gone through or under, leaving distinctive cubic feces. As wombats arrange these feces to mark territories and attract mates, it is believed that the cubic shape makes them more stackable and less to roll, which gives this shape a biological advantage; the method by which the wombat produces them is not well understood, but it is believed that the wombat intestine stretches preferentially at the walls. The adult wombat produces between 80 and 100, two-centimetre pieces of feces in a single night, four to eight pieces each bowel movement. Wombats are herbivores, their incisor teeth somewhat resemble those of rodents, being adapted for gnawing tough vegetation.
Like many other herbivorous mammals, they have a large diastema between their incisors and the cheek teeth, which are simple. The dental formula of wombats is 1.0.1.41.0.1.4 × 2 = 24. Wombats' fur can vary from a sandy colour from grey to black. All three known extant species weigh between 20 and 35 kg. Female wombats give birth to a single young in the spring, after a gestation period, which like all marsupials can vary, in the case of the wombat: 20–21 days, they have well-developed pouches. Wombats are weaned after 15 months, are sexually mature at 18 months. A group of wombats is known as a mob, or a colony. Wombats live up to 15 years in the wild, but can live past 20 and 30 years in captivity; the longest-lived captive wombat lived to 34 years of age. Wombats have an extraordinarily slow metabolism, taking around eight to 14 days to complete digestion, which aids their survival in arid conditions, they move slowly. When threatened, they can reach up to 40 km/h and maintain that speed for up to 90 seconds.
Wombats defend home territories centred on their burrows, they react aggressively to intruders. The common wombat occupies a range of up to 23 ha, while the hairy-nosed species have much smaller ranges, of no more than 4 ha. Dingos and Tasmanian devils prey on wombats. Extinct predators were to have included Thylacoleo and the thylacine, their primary defence is their toughened rear hide, with most of the posterior made of cartilage. This, combined with its lack of a meaningful tail, makes it difficult for any predator that follows the wombat into its tunnel to bite and injure its target; when attacked, wombats dive into a nearby tunnel. A wombat may allow an intruder to force its head over the wombat's back, use its powerful legs to crush the skull of the predator against the roof of the tunnel, or drive it off with two-legged kicks, like those of a donkey. Wombats are quiet animals. Bare-nosed wombats can make a number of more than the Hairy-nosed wombats. Wombats tend to be more vocal during mating season.
When angered, they can make hissing sounds. Their call sounds somewhat like a pig's squeal, they can make grunting noises, a low growl, a hoarse cough, a clicking noise. The three extant species of wombat all are endemic to a few offshore islands, they are protected under Australian law. Common wombat Northern hairy-nosed wombat or yaminon Southern hairy-nosed wombat Depiction of the animals in rock art are exceptionally rare, though examples estimated to be up to 4,000 years old have been discovered in the Wollemi National Park; the wombat is depicted in aboriginal Dreamtime as an animal of little worth. The mainland stories tell of the wombat as originating from a person named Warreen whose head had been flattened by a stone and tail amputated as punishment for selfishness. In contrast, the Tasmanian aboriginal story first recorded in 1830 tells of the wombat the great spirit Moihernee had asked hunters to leave alone. In both cases, the wombat is regarded as having been banished to its burrowing habitat.
Estimates of wombat distribution prior to European settlement are that numbers of all three surviving species were prolific and that they
Spotted hyena
The spotted hyena known as the laughing hyena, is a hyena species classed as the sole member of the genus Crocuta, native to Sub-Saharan Africa. It is listed as being of least concern by the IUCN on account of its widespread range and large numbers estimated between 27,000 and 47,000 individuals; the species is, experiencing declines outside of protected areas due to habitat loss and poaching. The species may have originated in Asia, once ranged throughout Europe for at least one million years until the end of the Late Pleistocene; the spotted hyena is the largest known member of the Hyaenidae, is further physically distinguished from other species by its vaguely bear-like build, its rounded ears, its less prominent mane, its spotted pelt, its more dual purposed dentition, its fewer nipples and the presence of a pseudo-penis in the female. It is the only mammalian species to lack an external vaginal opening; the spotted hyena is the most social of the Carnivora in that it has the largest group sizes and most complex social behaviours.
Its social organisation is unlike that of any other carnivore, bearing closer resemblance to that of cercopithecine primates with respect to group-size, hierarchical structure, frequency of social interaction among both kin and unrelated group-mates. However, the social system of the spotted hyena is competitive rather than cooperative, with access to kills, mating opportunities and the time of dispersal for males depending on the ability to dominate other clan-members. Females provide only for their own cubs rather than assist each other, males display no paternal care. Spotted hyena society is matriarchal; the spotted hyena is a successful animal, being the most common large carnivore in Africa. Its success is due in part to its opportunism. In functional terms, the spotted hyena makes the most efficient use of animal matter of all African carnivores; the spotted hyena displays greater plasticity in its hunting and foraging behaviour than other African carnivores. During a hunt, spotted hyenas run through ungulate herds in order to select an individual to attack.
Once selected, their prey is chased over a long distance several kilometres, at speeds of up to 60 km/h. The spotted hyena has a long history of interaction with humanity; the species has a negative reputation in both Western culture and African folklore. In the former, the species is regarded as ugly and cowardly, while in the latter, it is viewed as greedy, gluttonous and foolish, yet powerful and dangerous; the majority of Western perceptions on the species can be found in the writings of Aristotle and Pliny the Elder, though in unjudgemental form. Explicit, negative judgements occur in the Physiologus, where the animal is depicted as a hermaphrodite and grave-robber; the IUCN's hyena specialist group identifies the spotted hyena's negative reputation as detrimental to the species' continued survival, both in captivity and the wild. The spotted hyena's scientific name Crocuta, was once thought to be derived from the Latin loanword crocutus, which translates as "saffron-coloured one", in reference to the animal's fur colour.
This was proven to be incorrect, as the correct spelling of the loanword would have been Crocāta, the word was never used in that sense by Graeco-Roman sources. Crocuta comes from the Ancient Greek word Κροκόττας, derived from the Sanskrit koṭṭhâraka, which in turn originates from kroshṭuka; the earliest recorded mention of Κροκόττας is from Strabo's Geographica, where the animal is described as a mix of wolf and dog native to Ethiopia. From Classical antiquity until the Renaissance, the spotted and striped hyena were either assumed to be the same species, or distinguished purely on geographical, rather than physical grounds. Hiob Ludolf, in his Historia aethiopica, was the first to distinguish the Crocuta from Hyaena on account of physical, as well as geographical grounds, though he never had any first hand experience of the species, having gotten his accounts from an Ethiopian intermediary. Confusion still persisted over the exact taxonomic nature of the hyena family in general, with most European travelers in Ethiopia referring to hyenas as "wolves".
This stems from the Amharic word for hyena, ጅብ, linked to the Arabic word ذئب "wolf". The first detailed first-hand descriptions of the spotted hyena by Europeans come from Willem Bosman and Peter Kolbe. Bosman, a Dutch tradesman who worked for the Dutch West India Company at the Gold Coast from 1688–1701, wrote of "Jakhals, of Boshond" whose physical descriptions match the spotted hyena. Kolben, a German mathematician and astronomer who worked for the Dutch East India Company in the Cape of Good Hope from 1705–1713, described the spotted hyena in great detail, but referred to it as a "tigerwolf", because the settlers in southern Africa did not know of hyenas, thus labelled them as "wolves". Bosman and Kolben's descriptions went unnoticed until 1771, when the Welsh naturalist Thomas Pennant, in his Synopsis of Quadrupeds, used the descriptions, as well as his personal experience with a captive specimen, as a basis for differentiating the spotted hyena from the striped; the descrip
Guinea pig
The guinea pig or domestic guinea pig known as cavy or domestic cavy, is a species of rodent belonging to the family Caviidae and the genus Cavia. Despite their common name, guinea pigs are not native to Guinea, nor are they biologically related to pigs, the origin of the name is still unclear, they originated in the Andes of South America, studies based on biochemistry and hybridization suggest they are domesticated descendants of a related species of cavy such as C. tschudii, therefore do not exist in the wild. In Western society, the domestic guinea pig has enjoyed widespread popularity as a household pet, a type of pocket pet, since its introduction by European traders in the 16th century, their docile nature, friendly responsiveness to handling and feeding, the relative ease of caring for them have made and continue to make guinea pigs a popular choice of pet. Organizations devoted to the competitive breeding of guinea pigs have been formed worldwide, many specialized breeds with varying coat colors and textures are selected by breeders.
The domestic guinea pig plays an important role in folk culture for many indigenous Andean groups as a food source, but in folk medicine and in community religious ceremonies. The animals are used for meat and are a culinary staple in the Andes Mountains, where they are known as cuy. A modern breeding program was started in the 1960s in Peru that resulted in large breeds known as cuy mejorados and prompted efforts to increase consumption of the animal outside South America. Biological experimentation on domestic guinea pigs has been carried out since the 17th century; the animals were so used as model organisms in the 19th and 20th centuries that the epithet guinea pig came into use to describe a human test subject. Since that time, they have been replaced by other rodents such as mice and rats. However, they are still used in research as models for human medical conditions such as juvenile diabetes, tuberculosis and pregnancy complications; the scientific name of the common species is Cavia porcellus, with porcellus being Latin for "little pig".
Cavia is New Latin. Cabiai may be an adaptation of the Portuguese çavia, itself derived from the Tupi word saujá, meaning rat. Guinea pigs are called quwi or jaca in Quechua and cuy or cuyo in the Spanish of Ecuador and Bolivia. Breeders tend to use the more formal "cavy" to describe the animal, while in scientific and laboratory contexts, it is far more referred to by the more colloquial "guinea pig". How the animals came to be called "pigs" is not clear, they are built somewhat like pigs, with large heads relative to their bodies, stout necks, rounded rumps with no tail of any consequence. They can survive for long periods in small quarters, like a'pig pen', were thus transported on ships to Europe; the animal's name alludes to pigs in many European languages. The German word for them is Meerschweinchen "little sea pig", translated into Polish as świnka morska, into Hungarian as tengerimalac, into Russian as морская свинка; this derives from the Middle High German name merswin. This meant "dolphin" and was used because of the animals' grunting sounds.
Many other less scientifically based explanations of the German name exist. For example, sailing ships stopping to reprovision in the New World would pick up stores of guinea pigs, which provided an transportable source of fresh meat; the French term is cochon cobaye. This is not universal; the Chinese refer to them as 豚鼠, sometimes as Netherlands pig or Indian mouse. The Japanese word for guinea pig is "モルモット", which derives from the name of another mountain-dwelling rodent, the marmot; the other Japanese word for guinea pig, using kanji, is tenjiku-nezumi, which translates as India rat. The origin of "guinea" in "guinea pig" is harder to explain. One proposed explanation is that the animals were brought to Europe by way of Guinea, leading people to think they had originated there. "Guinea" was frequently used in English to refer to any far-off, unknown country, so the name may be a colorful reference to the animal's exotic appeal. Another hypothesis suggests the "guinea" in the name is a corruption of "Guiana", an area in South America.
A common misconception is that they were so named because they were sold for the price of a guinea coin. Others believe; the guinea pig was first domesticated as early as 5000 BC for food by tribes in the Andean region of South America (the present-day sout
Moose
The moose or elk, Alces alces is a member of the New World deer subfamily and is the largest and heaviest extant species in the Deer family. Moose are distinguished by the palmate antlers of the males. Moose inhabit boreal forests and temperate broadleaf and mixed forests of the Northern Hemisphere in temperate to subarctic climates. Hunting and other human activities have caused a reduction in the size of the moose's range over time. Moose have been reintroduced to some of their former habitats. Most moose are found in Canada, New England, Baltic states, Russia, their diet consists of both aquatic vegetation. The most common moose predators are the gray wolf along with humans. Unlike most other deer species, moose do not form herds and are solitary animals, aside from calves who remain with their mother until the cow begins estrus, at which point the cow chases away young bulls. Although slow-moving and sedentary, moose can become aggressive and move if angered or startled, their mating season in the autumn features energetic fights between males competing for a female.
Alces alces is called an "elk" in British English. The word "elk" in North American English refers to a different species of deer, the Cervus canadensis called the wapiti. A mature male moose is called a bull, a mature female a cow, an immature moose of either sex a calf; the word "elk" originated in Proto-Germanic, from which Old English evolved and has cognates in other Indo-European languages, e.g. elg in Danish/Norwegian. In the continental-European languages, these forms of the word "elk" always refer to the Alces alces; the word "moose" had first entered English by 1606 and is borrowed from the Algonquian languages, involved forms from multiple languages mutually reinforcing one another. The Proto-Algonquian form was *mo·swa; the moose became extinct in Britain during the Bronze Age, long before the European arrival in the Americas. The youngest bones were found in Scotland and are 3,900 years old; the word "elk" remained in usage because of its existence in continental Europe but, without any living animals around to serve as a reference, the meaning became rather vague to most speakers of English, who used "elk" to refer to "large deer" in general.
Dictionaries of the 18th century described "elk" as a deer, "as large as a horse". Confusingly, the word "elk" is used in North America to refer to a different animal, Cervus canadensis, called by the Algonquian indigenous name, "wapiti"; the British began colonizing America in the 17th century, found two common species of deer for which they had no names. The wapiti appeared similar to the red deer of Europe although it was much larger and was not red; the moose was a rather strange-looking deer to the colonists, they adopted local names for both. In the early days of American colonization, the wapiti was called a grey moose and the moose was called a black moose, but early accounts of the animals varied wildly, adding to the confusion; the wapiti is superficially similar to the red deer of central and western Europe, although it is distinctly different behaviorally and genetically. Early European explorers in North America in Virginia where there were no moose, called the wapiti "elk" because of its size and resemblance to familiar-looking deer like the red deer.
The moose resembled the "German elk", less familiar to the British colonists. For a long time neither species were called a variety of things. In North America the wapiti became known as an elk while the moose retained its Anglicized Native-American name. In 1736, Samuel Dale wrote to the Royal Society of Great Britain: The common light-grey moose, called by the Indians and the large or black-moose, the beast whose horns I herewith present; as to the grey moose, I take it to be no larger than what Mr. John Clayton, in his account of the Virginia Quadrupeds, calls the Elke... was in all respects like those of our red-deer or stags, only larger... The black moose is accounted a large creature.... The stag, buck, or male of this kind has a palmed horn, not like that of our common or fallow-deer, but the palm is much longer, more like that of the German elke. Moose require habitat with adequate edible plants, cover from predators, protection from hot or cold weather. Moose travel among different habitats with the seasons to address these requirements.
Moose are cold-adapted mammals with thickened skin, heat-retaining coat, a low surface:volume ratio, which provides excellent cold tolerance but poor heat tolerance. Moose survive hot weather by immersion in cool water. In hot weather, moose are found wading or swimming in lakes or ponds; when heat-stressed, moose may fail to adequately forage in summer and may not gain adequate body fat to survive the winter. Also
Anti-predator adaptation
Anti-predator adaptations are mechanisms developed through evolution that assist prey organisms in their constant struggle against predators. Throughout the animal kingdom, adaptations have evolved for every stage of this struggle, namely by avoiding detection, warding off attack, fighting back, or escaping when caught; the first line of defence consists in avoiding detection, through mechanisms such as camouflage, apostatic selection, living underground, or nocturnality. Alternatively, prey animals may ward off attack, whether by advertising the presence of strong defences in aposematism, by mimicking animals which do possess such defences, by startling the attacker, by signalling to the predator that pursuit is not worthwhile, by distraction, by using defensive structures such as spines, by living in a group. Members of groups are at reduced risk of predation, despite the increased conspicuousness of a group, through improved vigilance, predator confusion, the likelihood that the predator will attack some other individual.
Some prey species are capable of fighting back against predators, whether with chemicals, through communal defence, or by ejecting noxious materials. Many animals can escape by fleeing outrunning or outmanoeuvring their attacker; some species are able to escape when caught by sacrificing certain body parts: crabs can shed a claw, while lizards can shed their tails distracting predators long enough to permit the prey to escape. Animals may avoid becoming prey by living out of sight of predators, whether in caves, burrows, or by being nocturnal. Nocturnality is an animal behavior characterized by activity during the night and sleeping during the day; this is a behavioral form of detection avoidance called crypsis used by animals to either avoid predation or to enhance prey hunting. Predation risk has long been recognized as critical in shaping behavioral decisions. For example, this predation risk is of prime importance in determining the time of evening emergence in echolocating bats. Although early access during brighter times permits easier foraging, it leads to a higher predation risk from bat hawks and bat falcons.
This results in an optimum evening emergence time, a compromise between the conflicting demands. Another nocturnal adaptation can be seen in kangaroo rats, they forage in open habitats, reduce their activity outside their nest burrows in response to moonlight. During a full moon, they shift their activity towards areas of dense cover to compensate for the extra brightness. Camouflage uses any combination of materials, coloration, or illumination for concealment to make the organism hard to detect by sight, it is common in both marine animals. Camouflage can be achieved in many different ways, such as through resemblance to surroundings, disruptive coloration, shadow elimination by countershading or counter-illumination, self-decoration, cryptic behavior, or changeable skin patterns and colour. Animals such as the flat-tail horned lizard of North America have evolved to eliminate their shadow and blend in with the ground; the bodies of these lizards are flattened, their sides thin towards the edge.
This body form, along with the white scales fringed along their sides, allows the lizards to hide their shadows. In addition, these lizards hide any remaining shadows by pressing their bodies to the ground. Animals can hide in plain sight by masquerading as inedible objects. For example, the potoo, a South American bird, habitually perches on a tree, convincingly resembling a broken stump of a branch, while a butterfly, looks just like a dead leaf. Another way to remain unattacked in plain sight is to look different from other members of the same species. Predators such as tits selectively hunt for abundant types of insect, ignoring less common types that were present, forming search images of the desired prey; this creates a mechanism for apostatic selection. Many species make use of behavioral strategies to deter predators. Many weakly-defended animals, including moths, mantises and cephalopods such as octopuses, make use of patterns of threatening or startling behaviour, such as displaying conspicuous eyespots, so as to scare off or momentarily distract a predator, thus giving the prey animal an opportunity to escape.
In the absence of toxins or other defences, this is bluffing, in contrast to aposematism which involves honest signals. Pursuit-deterrent signals are behavioral signals used by prey that convince predators not to pursue them. For example, gazelles stot, jumping high with an arched back; this is thought to signal to predators that they have a high level of fitness and can outrun the predator. As a result, predators may choose to pursue a different prey, less to outrun them. White-tailed deer and other prey mammals flag with conspicuous tail markings when alarmed, informing the predator that it has been detected. Warning calls given by birds such as the Eurasian jay are honest signals, benefiting both predator and prey: the predator is informed that it has been detected and might as well save time and energy by giving up the chase, while the prey is protected from attack. Another pursuit-deterrent signal is thanatosis or playing dead. Thanatosis is a form of bluff in which an animal mimics its own dead body, feigning death to avoid being attacked by predators seeking live prey.
Thanatosis can be used by the predator in order to lure prey into approaching. An example of this is seen in white-tailed deer fawns, which experience a drop in heart rate in response to approaching predators; this response, referred to as "alarm bradycardia", causes the fawn's heart rate to drop
Animal
Animals are multicellular eukaryotic organisms that form the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, grow from a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. Animals range in length from 8.5 millionths of a metre to 33.6 metres and have complex interactions with each other and their environments, forming intricate food webs. The category includes humans, but in colloquial use the term animal refers only to non-human animals; the study of non-human animals is known as zoology. Most living animal species are in the Bilateria, a clade whose members have a bilaterally symmetric body plan; the Bilateria include the protostomes—in which many groups of invertebrates are found, such as nematodes and molluscs—and the deuterostomes, containing the echinoderms and chordates.
Life forms interpreted. Many modern animal phyla became established in the fossil record as marine species during the Cambrian explosion which began around 542 million years ago. 6,331 groups of genes common to all living animals have been identified. Aristotle divided animals into those with those without. Carl Linnaeus created 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 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 the evolutionary relationships between animal taxa. Humans make use of many other animal species for food, including meat and eggs. Dogs have been used in hunting, while many aquatic animals are hunted for sport.
Non-human animals have appeared in art from the earliest times and are featured in mythology and religion. The word "animal" comes from the Latin animalis, having soul or living being; the biological definition includes all members of the kingdom Animalia. In colloquial usage, as a consequence of anthropocentrism, the term animal is sometimes used nonscientifically to refer only to non-human animals. Animals have several characteristics. Animals are eukaryotic and multicellular, unlike bacteria, which are prokaryotic, unlike protists, which are eukaryotic but unicellular. Unlike plants and algae, which produce their own nutrients animals are heterotrophic, feeding on organic material and digesting it internally. With few exceptions, animals breathe oxygen and respire aerobically. All animals are motile during at least part of their life cycle, but some animals, such as sponges, corals and barnacles become sessile; the blastula is a stage in embryonic development, unique to most 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 flexible framework upon which cells can move about and be reorganised, making the formation of complex structures possible; this may be calcified, forming structures such as shells and spicules. In contrast, the cells of other multicellular organisms are held in place by cell walls, so develop by progressive growth. Animal cells uniquely possess the cell junctions called tight junctions, gap junctions, desmosomes. With few exceptions—in particular, the sponges and placozoans—animal bodies are differentiated into tissues; these include muscles, which enable locomotion, nerve tissues, which transmit signals and coordinate the body. There is an internal digestive chamber with either one opening or two openings. Nearly all animals make use of some form of sexual reproduction, they produce haploid gametes by meiosis.
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, develop into a new sponge. In most other groups, the blastula undergoes more complicated rearrangement, it first invaginates to form 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 develops between them; these germ layers differentiate to form tissues and organs. Repeated instances of mating with a close relative during sexual reproduction leads to inbreeding depression within a population due to the increased prevalence of harmful recessive traits. Animals have evolved numerous mechanisms for avoiding close inbreeding. In some species, such as the splendid fairywren, females benefit by mating with multiple males, thus producing more offspring of higher genetic quality; some animals are capable of asexual reproduction, which results
