Wool is the textile fiber obtained from sheep and other animals, including cashmere and mohair from goats, qiviut from muskoxen, from hide and fur clothing from bison, angora from rabbits, other types of wool from camelids. Wool consists of protein together with a few percent lipids. In this regard it is chemically quite distinct from the more dominant textile, cellulose. Wool is produced by follicles; these follicles are located in the upper layer of the skin called the epidermis and push down into the second skin layer called the dermis as the wool fibers grow. Follicles can be classed as either secondary follicles. Primary follicles produce three types of fiber: kemp, medullated fibers, true wool fibers. Secondary follicles only produce true wool fibers. Medullated fibers share nearly identical characteristics to hair and are long but lack crimp and elasticity. Kemp fibers are coarse and shed out. Wool's scaling and crimp make it easier to spin the fleece by helping the individual fibers attach to each other, so they stay together.
Because of the crimp, wool fabrics have greater bulk than other textiles, they hold air, which causes the fabric to retain heat. Wool has a high specific thermal resistance, so it impedes heat transfer in general; this effect has benefited desert peoples, as Tuaregs use wool clothes for insulation. Felting of wool occurs upon hammering or other mechanical agitation as the microscopic barbs on the surface of wool fibers hook together. Wool has several qualities that distinguish it from hair/fur: it is crimped and elastic; the amount of crimp corresponds to the fineness of the wool fibers. A fine wool like Merino may have up to 100 crimps per inch, while coarser wool like karakul may have as few as one or two. In contrast, hair has little if any scale and no crimp, little ability to bind into yarn. On sheep, the hair part of the fleece is called kemp; the relative amounts of kemp to wool vary from breed to breed and make some fleeces more desirable for spinning, felting, or carding into batts for quilts or other insulating products, including the famous tweed cloth of Scotland.
Wool fibers absorb moisture, but are not hollow. Wool can absorb one-third of its own weight in water. Wool absorbs sound like many other fabrics, it is a creamy white color, although some breeds of sheep produce natural colors, such as black, brown and random mixes. Wool ignites at a higher temperature than some synthetic fibers, it has a lower rate of flame spread, a lower rate of heat release, a lower heat of combustion, does not melt or drip. Wool carpets are specified for high safety environments, such as trains and aircraft. Wool is specified for garments for firefighters and others in occupations where they are exposed to the likelihood of fire. Wool causes an allergic reaction in some people. Sheep shearing is the process. After shearing, the wool is separated into four main categories: fleece, broken and locks; the quality of fleeces is determined by a technique known as wool classing, whereby a qualified person, called a wool classer, groups wools of similar gradings together to maximize the return for the farmer or sheep owner.
In Australia before being auctioned, all Merino fleece wool is objectively measured for micron, staple length, staple strength, sometimes color and comfort factor. Wool straight off a sheep, known as "greasy wool" or "wool in the grease", contains a high level of valuable lanolin, as well as the sheep's dead skin and sweat residue, also contains pesticides and vegetable matter from the animal's environment. Before the wool can be used for commercial purposes, it must be scoured, a process of cleaning the greasy wool. Scouring may be as simple as a bath in warm water or as complicated as an industrial process using detergent and alkali in specialized equipment. In north west England, special potash pits were constructed to produce potash used in the manufacture of a soft soap for scouring locally produced white wool. In commercial wool, vegetable matter is removed by chemical carbonization. In less-processed wools, vegetable matter may be removed by hand and some of the lanolin left intact through the use of gentler detergents.
This semigrease wool can be worked into yarn and knitted into water-resistant mittens or sweaters, such as those of the Aran Island fishermen. Lanolin removed from wool is used in cosmetic products, such as hand creams. Raw wool has many impurities; the sheep's body yields many types of wool with differing strengths, length of staple and impurities. The raw wool is processed into'top'.'Worsted top' requires strong straight and parallel fibres. The quality of wool is determined by its fiber diameter, yield and staple strength. Fiber diameter is the single most important wool characteristic determining price. Merino wool is 3–5 inches in length and is fine; the finest and most valuable wool comes from Merino hoggets. Wool taken from sheep produced for meat is more coarse, has fibers 1.5 to 6 in in length. Damage or breaks in the wool can occur if the sheep is stressed whil
Poaceae or Gramineae is a large and nearly ubiquitous family of monocotyledonous flowering plants known as grasses referred to collectively as grass. Poaceae includes the cereal grasses and the grasses of natural grassland and cultivated lawns and pasture. Grasses have stems that are hollow except at the nodes and narrow alternate leaves borne in two ranks; the lower part of each leaf encloses the stem. With around 780 genera and around 12,000 species, Poaceae are the fifth-largest plant family, following the Asteraceae, Orchidaceae and Rubiaceae. Grasslands such as savannah and prairie where grasses are dominant are estimated to constitute 40.5% of the land area of the Earth, excluding Greenland and Antarctica. Grasses are an important part of the vegetation in many other habitats, including wetlands and tundra; the Poaceae are the most economically important plant family, providing staple foods from domesticated cereal crops such as maize, rice and millet as well as forage, building materials and fuel.
Though they are called "grasses", seagrasses and sedges fall outside this family. The rushes and sedges are related to the Poaceae, being members of the order Poales, but the seagrasses are members of order Alismatales; the name Poaceae was given by John Hendley Barnhart in 1895, based on the tribe Poeae described in 1814 by Robert Brown, the type genus Poa described in 1753 by Carl Linnaeus. The term is derived from the Ancient Greek πόα. Grasses include some of the most versatile plant life-forms, they became widespread toward the end of the Cretaceous period, fossilized dinosaur dung have been found containing phytoliths of a variety that include grasses that are related to modern rice and bamboo. Grasses have adapted to conditions in lush rain forests, dry deserts, cold mountains and intertidal habitats, are the most widespread plant type. A cladogram shows subfamilies and approximate species numbers in brackets: Before 2005, fossil findings indicated that grasses evolved around 55 million years ago.
Recent findings of grass-like phytoliths in Cretaceous dinosaur coprolites have pushed this date back to 66 million years ago. In 2011, revised dating of the origins of the rice tribe Oryzeae suggested a date as early as 107 to 129 Mya. Wu, You & Li described grass microfossils extracted from a specimen of the hadrosauroid dinosaur Equijubus normani from the Early Cretaceous Zhonggou Formation; the authors noted that India became separated from Antarctica, therefore all other continents at the beginning of late Aptian, so the presence of grasses in both India and China during the Cretaceous indicates that the ancestor of Indian grasses must have existed before late Aptian. Wu, You & Li considered the Barremian origin for grasses to be probableThe relationships among the three subfamilies Bambusoideae and Pooideae in the BOP clade have been resolved: Bambusoideae and Pooideae are more related to each other than to Oryzoideae; this separation occurred within the short time span of about 4 million years.
According to Lester Charles King the spread of grasses in the Late Cenozoic would have changed patterns of hillslope evolution favouring slopes that are convex upslope and concave downslope and lacking a free face were common. King argued that this was the result of more acting surface wash caused by carpets of grass which in turn would have resulted in more soil creep. Grasses may be annual or perennial herbs with the following characteristics: The stems of grasses, called culms, are cylindrical and are hollow, plugged at the nodes, where the leaves are attached. Grass leaves are nearly always alternate and distichous, have parallel veins; each leaf is differentiated into a lower sheath hugging a blade with entire margins. The leaf blades of many grasses are hardened with silica phytoliths, which discourage grazing animals. A membranous appendage or fringe of hairs called the ligule lies at the junction between sheath and blade, preventing water or insects from penetrating into the sheath. Flowers of Poaceae are characteristically arranged in each having one or more florets.
The spikelets are further grouped into spikes. The part of the spikelet that bears the florets is called the rachilla. A spikelet consists of two bracts at called glumes, followed by one or more florets. A floret consists of the flower surrounded by two bracts, one external—the lemma—and one internal—the palea; the flowers are hermaphroditic—maize being an important exception—and anemophilous or wind-pollinated, although insects play a role. The perianth is reduced to two scales, called lodicules, that expand and contract to spread the lemma and palea; this complex structure can be seen in the image on the right. The fruit of grasses is a caryopsis. A tiller is a leafy shoot other than the first shoot produced from the seed. Grass blades grow at the base of the blade and not from elongated stem tips; this low growth point evolved in response to grazing animals and allows grasses to be grazed or mown without severe damage to the plant. Three general classifications of growth habit present in g
Meat is animal flesh, eaten as food. Humans have killed animals for meat since prehistoric times; the advent of civilization allowed the domestication of animals such as chickens, rabbits and cattle. This led to their use in meat production on an industrial scale with the aid of slaughterhouses. Meat is composed of water and fat, it is edible raw, but is eaten after it has been cooked and seasoned or processed in a variety of ways. Unprocessed meat will spoil or rot within hours or days as a result of infection with and decomposition by bacteria and fungi. Meat is important in economy and culture though its mass production and consumption has been determined to pose risks for human health and the environment. Many religions have rules about which meat may not be eaten. Vegetarians may abstain from eating meat because of concerns about the ethics of eating meat, environmental effects of meat production or nutritional effects of consumption; the word meat comes from the Old English word mete. The term is related to mad in Danish, mat in Swedish and Norwegian, matur in Icelandic and Faroese, which mean'food'.
The word mete exists in Old Frisian to denote important food, differentiating it from swiets and dierfied. Most meat refers to skeletal muscle and associated fat and other tissues, but it may describe other edible tissues such as offal. Meat is sometimes used in a more restrictive sense to mean the flesh of mammalian species raised and prepared for human consumption, to the exclusion of fish, other seafood, poultry, or other animals. In the context of food, meat can refer to "the edible part of something as distinguished from its covering", for example, coconut meat. Paleontological evidence suggests that meat constituted a substantial proportion of the diet of the earliest humans. Early hunter-gatherers depended on the organized hunting of large animals such as bison and deer; the domestication of animals, of which we have evidence dating back to the end of the last glacial period, allowed the systematic production of meat and the breeding of animals with a view to improving meat production.
Animals that are now principal sources of meat were domesticated in conjunction with the development of early civilizations: Sheep, originating from western Asia, were domesticated with the help of dogs prior to the establishment of settled agriculture as early as the 8th millennium BCE. Several breeds of sheep were established in ancient Mesopotamia and Egypt by 3500–3000 BCE. Today, more than 200 sheep-breeds exist. Cattle were domesticated in Mesopotamia after settled agriculture was established about 5000 BCE, several breeds were established by 2500 BCE. Modern domesticated cattle fall into the groups Bos taurus and Bos taurus indicus, both descended from the now-extinct aurochs; the breeding of beef cattle, cattle optimized for meat production as opposed to animals best suited for work or dairy purposes, began in the middle of the 18th century. Domestic pigs, which are descended from wild boars, are known to have existed about 2500 BCE in modern-day Hungary and in Troy. Pork sausages and hams were of great commercial importance in Greco-Roman times.
Pigs continue to be bred intensively as they are being optimized to produce meat best suited for specific meat products. Other animals have been raised or hunted for their flesh; the type of meat consumed varies much between different cultures, changes over time, depending on factors such as tradition and the availability of the animals. The amount and kind of meat consumed varies by income, both between countries and within a given country. Horses are eaten in France, Italy and Japan, among other countries. Horses and other large mammals such as reindeer were hunted during the late Paleolithic in western Europe. Dogs are consumed in South Korea and Vietnam. Dogs are occasionally eaten in the Arctic regions. Dog meat has been consumed in various parts of the world, such as Hawaii, Japan and Mexico. Cats are consumed in Southern China and sometimes in Northern Italy. Guinea pigs are raised for their flesh in the Andes. Whales and dolphins are hunted for their flesh, in Japan, Siberia, the Faroe Islands, Iceland, Saint Vincent and the Grenadines and by two small communities in Indonesia.
Modern agriculture employs a number of techniques, such as progeny testing, to speed artificial selection by breeding animals to acquire the qualities desired by meat producers. For instance, in the wake of well-publicised health concerns associated with saturated fats in the 1980s, the fat content of United Kingdom beef and lamb fell from 20–26 percent to 4–8 percent within a few decades, due to both selective breeding for leanness and changed methods of butchery. Methods of genetic engineering aimed at improving the meat production qualities of animals are now becoming available. Though it is a old industry, meat production continues to be shaped by the evolving demands of customers; the trend towards selling meat in pre-packaged cuts has increased the demand for larger breeds of cattle, which are better suited to producing such cuts. More animals not exploited for their meat are now being farmed the more agile and mobile species, whose muscles tend to be developed better than those of cattle, sheep or pigs.
Examples are the various antelope species, the zebra, water buffalo and camel, as well as non-
Mammals are vertebrate animals constituting the class Mammalia, characterized by the presence of mammary glands which in females produce milk for feeding their young, a neocortex, fur or hair, three middle ear bones. These characteristics distinguish them from reptiles and birds, from which they diverged in the late Triassic, 201–227 million years ago. There are around 5,450 species of mammals; the largest orders are the rodents and Soricomorpha. The next three are the Primates, the Cetartiodactyla, the Carnivora. In cladistics, which reflect evolution, mammals are classified as endothermic amniotes, they are the only living Synapsida. The early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period around 300 million years ago, this group diverged from the sauropsid line that led to today's reptiles and birds; the line following the stem group Sphenacodontia split off several diverse groups of non-mammalian synapsids—sometimes referred to as mammal-like reptiles—before giving rise to the proto-mammals in the early Mesozoic era.
The modern mammalian orders arose in the Paleogene and Neogene periods of the Cenozoic era, after the extinction of non-avian dinosaurs, have been among the dominant terrestrial animal groups from 66 million years ago to the present. The basic body type is quadruped, most mammals use their four extremities for terrestrial locomotion. Mammals range in size from the 30–40 mm bumblebee bat to the 30-meter blue whale—the largest animal on the planet. Maximum lifespan varies from two years for the shrew to 211 years for the bowhead whale. All modern mammals give birth to live young, except the five species of monotremes, which are egg-laying mammals; the most species-rich group of mammals, the cohort called placentals, have a placenta, which enables the feeding of the fetus during gestation. Most mammals are intelligent, with some possessing large brains, self-awareness, tool use. Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals and echolocation.
Mammals can organize themselves into fission-fusion societies and hierarchies—but can be solitary and territorial. Most mammals are polygynous. Domestication of many types of mammals by humans played a major role in the Neolithic revolution, resulted in farming replacing hunting and gathering as the primary source of food for humans; this led to a major restructuring of human societies from nomadic to sedentary, with more co-operation among larger and larger groups, the development of the first civilizations. Domesticated mammals provided, continue to provide, power for transport and agriculture, as well as food and leather. Mammals are hunted and raced for sport, are used as model organisms in science. Mammals have been depicted in art since Palaeolithic times, appear in literature, film and religion. Decline in numbers and extinction of many mammals is driven by human poaching and habitat destruction deforestation. Mammal classification has been through several iterations since Carl Linnaeus defined the class.
No classification system is universally accepted. George Gaylord Simpson's "Principles of Classification and a Classification of Mammals" provides systematics of mammal origins and relationships that were universally taught until the end of the 20th century. Since Simpson's classification, the paleontological record has been recalibrated, the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself through the new concept of cladistics. Though field work made Simpson's classification outdated, it remains the closest thing to an official classification of mammals. Most mammals, including the six most species-rich orders, belong to the placental group; the three largest orders in numbers of species are Rodentia: mice, porcupines, beavers and other gnawing mammals. The next three biggest orders, depending on the biological classification scheme used, are the Primates including the apes and lemurs. According to Mammal Species of the World, 5,416 species were identified in 2006.
These were grouped into 153 families and 29 orders. In 2008, the International Union for Conservation of Nature completed a five-year Global Mammal Assessment for its IUCN Red List, which counted 5,488 species. According to a research published in the Journal of Mammalogy in 2018, the number of recognized mammal species is 6,495 species included 96 extinct; the word "mammal" is modern, from the scientific name Mammalia coined by Carl Linnaeus in 1758, derived from the Latin mamma. In an influential 1988 paper, Timothy Rowe defined Mammalia phylogenetically as the crown group of mammals, the clade consisting of the most recent common ancestor of living monotremes and therian m
The wolf known as the grey/gray wolf or timber wolf, is a canine native to the wilderness and remote areas of Eurasia and North America. It is the largest extant member of its family, with males averaging 43 -- females 36 -- 38.5 kg. It is distinguished from other Canis species by its larger size and less pointed features on the ears and muzzle, its winter fur is long and bushy and predominantly a mottled gray in color, although nearly pure white and brown to black occur. Mammal Species of the World, a standard reference work in zoology, recognises 38 subspecies of C. lupus. The gray wolf is the second most specialized member of the genus Canis, after the Ethiopian wolf, as demonstrated by its morphological adaptations to hunting large prey, its more gregarious nature, its advanced expressive behavior, it is nonetheless related enough to smaller Canis species, such as the coyote, golden jackal, to produce fertile hybrids. It is the only species of Canis to have a range encompassing both Eurasia and North America, originated in Eurasia during the Pleistocene, colonizing North America on at least three separate occasions during the Rancholabrean.
It is a social animal, travelling in nuclear families consisting of a mated pair, accompanied by the pair's adult offspring. The gray wolf is an apex predator throughout its range, with only humans and tigers posing a serious threat to it, it feeds on large ungulates, though it eats smaller animals, livestock and garbage. A seven-year-old wolf is considered to be old, the maximum lifespan is about 16 years; the global gray wolf population is estimated to be 300,000. The gray wolf is one of the world's best-known and most-researched animals, with more books written about it than any other wildlife species, it has a long history of association with humans, having been despised and hunted in most pastoral communities because of its attacks on livestock, while conversely being respected in some agrarian and hunter-gatherer societies. Although the fear of wolves is pervasive in many human societies, the majority of recorded attacks on people have been attributed to animals suffering from rabies. Non-rabid wolves have attacked and killed people children, but this is rare, as wolves are few, live away from people, have developed a fear of humans from hunters and shepherds.
The English'wolf' stems from the Old English wulf, itself thought to be derived from the Proto-Germanic *wulfaz. The Latin lupus is a Sabine loanword. Both derive from the Proto-Indo-European root * lukwos; the species Canis lupus was first recorded by Carl Linnaeus in his publication Systema Naturae in 1758, with the Latin classification translating into the English words "dog wolf". The 37 subspecies of Canis lupus are listed under the designated common name of "wolf" in Mammal Species of the World, published in 2005; the nominate subspecies is the Eurasian wolf known as the common wolf. The subspecies includes the domestic dog, eastern wolf and red wolf, but lists C. l. italicus as a synonym of C. l. lupus. However, the classification of several as either species or subspecies has been challenged; the evolution of the wolf occurred over a geologic time scale of at least 300,000 years. The gray wolf Canis lupus is a adaptable species, able to exist in a range of environments and which possesses a wide distribution across the Holarctic.
Studies of modern gray wolves have identified distinct sub-populations that live in close proximity to each other. This variation in sub-populations is linked to differences in habitat – precipitation, temperature and prey specialization – which affect cranio-dental plasticity; the archaeological and paleontological records show gray wolf continuous presence for at least the last 300,000 years. This continuous presence contrasts with genomic analyses, which suggest that all modern wolves and dogs descend from a common ancestral wolf population that existed as as 20,000 years ago; these analyses indicate a population bottleneck, followed by a rapid radiation from an ancestral population at a time during, or just after, the Last Glacial Maximum. However, the geographic origin of this radiation is not known. In 2018, whole genome sequencing was used to compare members of the genus Canis, along with the dhole and the African hunting dog. There is evidence of gene flow between African golden wolves, golden jackals, gray wolves.
One African golden wolf from the Egyptian Sinai Peninsula showed high admixture with the Middle Eastern gray wolves and dogs, highlighting the role of the land bridge between the African and Eurasian continents in canid evolution. There was evidence of gene flow between golden jackals and Middle Eastern wolves, less so with European and Asian wolves, least with North American wolves; the study proposes that the golden jackal ancestry found in North American wolves may have occurred before the divergence of the Eurasian and North American gray wolves. The study indicates that the common ancestor of the coyote and gray wolf has genetically admixed with a ghost population of an extinct unidentified canid; the canid is genetically close to the dhole and has evolved after the divergence of the African hunting dog from the other canid species. The basal position of the coyote compared to the wolf is proposed to be due to the coyote retaining more of the mitochondrial genome of this unknown canid.
In 2013, a genetic study found that the wolf population in Europe was divided along a north-south axis and formed five major clusters. Three clusters were identified occupying southern and
Visual perception is the ability to interpret the surrounding environment using light in the visible spectrum reflected by the objects in the environment. This is different from visual acuity, which refers to how a person sees. A person can have problem with visual perceptual processing if he/she has 20/20 vision; the resulting perception is known as visual perception, sight, or vision. The various physiological components involved in vision are referred to collectively as the visual system, are the focus of much research in linguistics, cognitive science and molecular biology, collectively referred to as vision science; the visual system in animals allows individuals to assimilate information from their surroundings. The act of seeing starts when the cornea and the lens of the eye focuses light from its surroundings onto a light-sensitive membrane in the back of the eye, called the retina; the retina is part of the brain, isolated to serve as a transducer for the conversion of light into neuronal signals.
Based on feedback from the visual system, the lens of the eye adjusts its thickness to focus light on the photoreceptive cells of the retina known as the rods and cones, which detect the photons of light and respond by producing neural impulses. These signals are processed via complex feedforward and feedback processes by different parts of the brain, from the retina upstream to central ganglia in the brain. Note that up until now much of the above paragraph could apply to octopuses, worms and things more primitive. However, the following applies to mammals and birds: The retina in these more complex animals sends fibers to the lateral geniculate nucleus, to the primary and secondary visual cortex of the brain. Signals from the retina can travel directly from the retina to the superior colliculus; the perception of objects and the totality of the visual scene is accomplished by the visual association cortex. The visual association cortex combines all sensory information perceived by the striate cortex which contains thousands of modules that are part of modular neural networks.
The neurons in the striate cortex send axons to the extrastriate cortex, a region in the visual association cortex that surrounds the striate cortex. The human visual system is believed to perceive visible light in the range of wavelengths between 370 and 730 nanometers of the electromagnetic spectrum. However, some research suggests that humans can perceive light in wavelengths down to 340 nanometers the young; the major problem in visual perception is that what people see is not a translation of retinal stimuli. Thus people interested in perception have long struggled to explain what visual processing does to create what is seen. There were two major ancient Greek schools, providing a primitive explanation of how vision is carried out in the body; the first was the "emission theory" which maintained that vision occurs when rays emanate from the eyes and are intercepted by visual objects. If an object was seen directly it was by'means of rays' coming out of the eyes and again falling on the object.
A refracted image was, seen by'means of rays' as well, which came out of the eyes, traversed through the air, after refraction, fell on the visible object, sighted as the result of the movement of the rays from the eye. This theory was championed by scholars like their followers; the second school advocated the so-called'intro-mission' approach which sees vision as coming from something entering the eyes representative of the object. With its main propagators Aristotle and their followers, this theory seems to have some contact with modern theories of what vision is, but it remained only a speculation lacking any experimental foundation. Both schools of thought relied upon the principle that "like is only known by like", thus upon the notion that the eye was composed of some "internal fire" which interacted with the "external fire" of visible light and made vision possible. Plato makes this assertion in his dialogue Timaeus, in his De Sensu. Alhazen carried out many investigations and experiments on visual perception, extended the work of Ptolemy on binocular vision, commented on the anatomical works of Galen.
He was the first person to explain that vision occurs when light bounces on an object and is directed to one's eyes. Leonardo da Vinci is believed to be the first to recognize the special optical qualities of the eye, he wrote "The function of the human eye... was described by a large number of authors in a certain way. But I found it to be different." His main experimental finding was that there is only a distinct and clear vision at the line of sight—the optical line that ends at the fovea. Although he did not use these words he is the father of the modern distinction between foveal and peripheral vision. Issac Newton was the first to discover through experimentation, by isolating individual colors of the spectrum of light passing through a prism, that the visually perceived color of objects appeared due to the character
The even-toed ungulates are ungulates - hoofed animals - which bear weight on two of the five toes: their third and fourth toes. The other three toes are either present, vestigial, or pointing posteriorly. By contrast, odd-toed ungulates bear weight on one of the five toes: the third toe. Another difference between the two is that even-toed ungulates digest plant cellulose in one or more stomach chambers rather than in their intestine as the odd-toed ungulates do; the aquatic cetaceans evolved from even-toed ungulates, so modern taxonomic classification sometimes combines the Artiodactyla and Cetacea into the Cetartiodactyla. The 220 land-based even-toed ungulate species include pigs, hippopotamuses, llamas, mouse deer, giraffes, sheep and cattle. Many of these are of great dietary and cultural importance to humans; the oldest fossils of even-toed ungulates date back to the early Eocene. Since these findings simultaneously appeared in Europe and North America, it is difficult to determine the origin of artiodactyls.
The fossils are classified as belonging to the family Dichobunidae. These were small animals, some as small as a hare, with a slim build, lanky legs, a long tail, their hind legs were much longer than their front legs. The early to middle Eocene saw the emergence of the ancestors of most of today's mammals. Two widespread, but now extinct, families of even-toed ungulates were Enteledontidae and Anthracotheriidae. Entelodonts existed from the middle Eocene to the early Miocene in North America, they had a stocky body with short legs and a massive head, characterized by two humps on the lower jaw bone. Anthracotheres had a large, porcine build, with an elongated muzzle; this group appeared in the middle Eocene up until the Pliocene, spread throughout Eurasia and North America. Anthracothereres are thought to be the ancestors of hippos, probably led a similar aquatic lifestyle. Hippopotamuses appeared in the late Miocene and occupied Africa and Asia – they never got to the Americas; the camels were, during large parts of the Cenozoic, limited to North America.
Among the North American camels were groups like the short-legged Merycoidodontidae. They first developed a great diversity of species in North America. Only in the late Miocene or early Pliocene did they migrate from North America into Eurasia; the North American varieties became extinct around 10,000 years ago. Suina have been around since the Eocene. In the late Eocene or the Oligocene, two families stayed in Africa. South America was settled by even-toed ungulates only in the Pliocene, after the land bridge at the Isthmus of Panama formed some three million years ago. With only the peccaries and various species of capreoline deer, South America has comparatively fewer artiodactyl families than other continents, except Australia, which has no native species; the classification of artiodactyls was hotly debated because the ocean-dwelling cetaceans evolved from the land-dwelling even-toed ungulates. Some semiaquatic even-toed ungulates are more related to the ocean-dwelling cetaceans than to the other even-toed ungulates.
This makes the Artiodactyla as traditionally defined a paraphyletic taxon, since it includes animals descended from a common ancestor, but does not include all of its descendants. Phylogenetic classification only recognizes monophyletic taxa. To address this problem, the traditional order Artiodactyla and infraorder Cetacea are sometimes subsumed into the more inclusive Cetartiodactyla taxon. An alternative approach is to include both land-dwelling even-toed ungulates and ocean-dwelling cetaceans in a revised Artiodactyla taxon. Order Artiodactyla/Clade CetartiodactylaSuborder Tylopoda Family †Anoplotheriidae? Family †Cainotheriidae Family †Merycoidodontidae Family †Agriochoeridae Family Camelidae: camels and lamoids or llamas Family †Oromerycidae Family †Xiphodontidae Clade Artiofabula Suborder Suina Family Suidae: pigs Family Tayassuidae: peccaries Family †Sanitheriidae Clade Cetruminantia Clade CetancodontamorphaGenus †Andrewsarchus? Family †Entelodontidae Suborder Whippomorpha Family †Raoellidae Superfamily Dichobunoidea – paraphyletic to Cetacea and Raoellidae Family †Dichobunidae Family †Helohyidae Family †Choeropotamidae Family †Cebochoeridae Family †Mixtotheriidae Infraorder Ancodonta Family †Anthracotheriidae – paraphyletic to Hippopotamidae Family Hippopotamidae: hippos Infraorder Cetacea: whales Parvorder †Archaeoceti Family †Pakicetidae Family †Ambulocetidae Family †Remingtonocetidae Family †Basilosauridae Parvorder Mysticeti: baleen whales Superfamily Balaenoidea: right whales Family Balaenidae: greater right whales Family Cetotheriidae: pygmy right whale Superfamily Balaenopteroidea: large baleen whales Family Balaenopteridae: slender-back rorquals and humpback whale Family Eschrichtiidae: gray whale Parvorder Odontoceti: toothed whales Superfamily Delphinoidea: oceanic dolphins and others Family Delphinidae: oceanic t