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ssing the vulnerable aquatic larval stage. They are not found in the sea with the exception of one or two frogs that live in brackish water in mangrove swamps; the Anderson's salamander meanwhile occurs in brackish or salt water lakes. On land, amphibians are restricted to moist habitats because of the need to keep their skin damp. Modern amphibians have a simplified anatomy compared to their ancestors due to paedomorphosis, caused by two evolutionary trends miniaturization and an unusually large genome, which result in a slower growth and development rate compared to other vertebrates. Another reason for their size is associated with their rapid metamorphosis, which seems to have evolved only in the ancestors of lissamphibia; in all other known lines the development was much more gradual. Because a remodeling of the feeding apparatus means they don't eat during the metamorphosis, the metamorphosis has to go faster the smaller the individual is, so it happens at an early stage when the larvae are still small

. The largest species of salamanders don't go through a metamorphosis. Amphibians that lay eggs on land often go through the whole metamorphosis inside the egg. An anamniotic terrestrial egg is less than 1 cm in diameter due to diffusion problems, a size which puts a limit on the amount of posthatching growth. The smallest amphibian and vertebrate in the world is a microhylid frog from New Guinea Paedophryne amauensis first discovered in 2012. It has an average length of and is part of a genus that contains four of the world's ten smallest frog species. The largest living amphibian is the Chinese giant salamander Andrias davidianus but this is a great deal smaller than the largest amphibian that ever existedthe extinct Prionosuchus, a crocodilelike temnospondyl dating to 270 million years ago from the middle Permian of Brazil. The largest frog is the African Goliath frog Conraua goliath, which can reach and weigh . Amphibians are ectothermic coldblooded vertebrates that do not maintain their body temper

ature through internal physiological processes. Their metabolic rate is low and as a result, their food and energy requirements are limited. In the adult state, they have tear ducts and movable eyelids, and most species have ears that can detect airborne or ground vibrations. They have muscular tongues, which in many species can be protruded. Modern amphibians have fully ossified vertebrae with articular processes. Their ribs are usually short and may be fused to the vertebrae. Their skulls are mostly broad and short, and are often incompletely ossified. Their skin contains little keratin and lacks scales, apart from a few fishlike scales in certain caecilians. The skin contains many mucous glands and in some species, poison glands a type of granular gland. The hearts of amphibians have three chambers, two atria and one ventricle. They have a urinary bladder and nitrogenous waste products are excreted primarily as urea. Most amphibians lay their eggs in water and have aquatic larvae that undergo metamorphosis

to become terrestrial adults. Amphibians breathe by means of a pump action in which air is first drawn into the buccopharyngeal region through the nostrils. These are then closed and the air is forced into the lungs by contraction of the throat. They supplement this with gas exchange through the skin. Anura The order Anura from the Ancient Greek an meaning "without" and oura meaning "tail" comprises the frogs and toads. They usually have long hind limbs that fold underneath them, shorter forelimbs, webbed toes with no claws, no tails, large eyes and glandular moist skin. Members of this order with smooth skins are commonly referred to as frogs, while those with warty skins are known as toads. The difference is not a formal one taxonomically and there are numerous exceptions to this rule. Members of the family Bufonidae are known as the "true toads". Frogs range in size from the Goliath frog Conraua goliath of West Africa to the Paedophryne amauensis, first described in Papua New Guinea in 2012, which is

also the smallest known vertebrate. Although most species are associated with water and damp habitats, some are specialised to live in trees or in deserts. They are found worldwide except for polar areas. Anura is divided into three suborders that are broadly accepted by the scientific community, but the relationships between some families remain unclear. Future molecular studies should provide further insights into their evolutionary relationships. The suborder Archaeobatrachia contains four families of primitive frogs. These are Ascaphidae, Bombinatoridae, Discoglossidae and Leiopelmatidae which have few derived features and are probably paraphyletic with regard to other frog lineages. The six families in the more evolutionarily advanced suborder Mesobatrachia are the fossorial Megophryidae, Pelobatidae, Pelodytidae, Scaphiopodidae and Rhinophrynidae and the obligatorily aquatic Pipidae. These have certain characteristics that are intermediate between the two other suborders. Neobatrachia is by far the la

rgest suborder and includes the remaining families of modern frogs, including most common species. Ninetysix percent of the over 5,000 extant species of frog are neobatrachians. Caudata The order Caudata from the Latin cauda meaning "tail" consists of the salamanderselongated, lowslung animals that mostly resemble lizards in form. This is a symplesiomorphic trait and they are no more closely related to lizards than they are to mammals. Salamanders lack claws, have scalefree skins, either smooth or covered with tubercles, and tails that are usually flattened from side to side and often finned. They range in size from the Chinese giant salamander Andrias davidianus, which has been reported to grow to a length of , to the diminutive Thorius pennatulus from Mexico which seldom exceeds in length. Salamanders have a mostly Laurasian distribution, being present in much of the Holarctic region of the northern hemisphere. The family Plethodontidae is also found in Central America and South America north of the Ama

zon basin; South America was apparently invaded from Central America by about the start of the Miocene, 23 million years ago. Urodela is a name sometimes used for all the extant species of salamanders. Members of several salamander families have become paedomorphic and either fail to complete their metamorphosis or retain some larval characteristics as adults. Most salamanders are under long. They may be terrestrial or aquatic and many spend part of the year in each habitat. When on land, they mostly spend the day hidden under stones or logs or in dense vegetation, emerging in the evening and night to forage for worms, insects and other invertebrates. The suborder Cryptobranchoidea contains the primitive salamanders. A number of fossil cryptobranchids have been found, but there are only three living species, the Chinese giant salamander Andrias davidianus, the Japanese giant salamander Andrias japonicus and the hellbender Cryptobranchus alleganiensis from North America. These large amphibians retain several

larval characteristics in their adult state; gills slits are present and the eyes are unlidded. A unique feature is their ability to feed by suction, depressing either the left side of their lower jaw or the right. The males excavate nests, persuade females to lay their egg strings inside them, and guard them. As well as breathing with lungs, they respire through the many folds in their thin skin, which has capillaries close to the surface. The suborder Salamandroidea contains the advanced salamanders. They differ from the cryptobranchids by having fused prearticular bones in the lower jaw, and by using internal fertilisation. In salamandrids, the male deposits a bundle of sperm, the spermatophore, and the female picks it up and inserts it into her cloaca where the sperm is stored until the eggs are laid. The largest family in this group is Plethodontidae, the lungless salamanders, which includes 60 of all salamander species. The family Salamandridae includes the true salamanders and the name "newt" is give

n to members of its subfamily Pleurodelinae. The third suborder, Sirenoidea, contains the four species of sirens, which are in a single family, Sirenidae. Members of this order are eellike aquatic salamanders with much reduced forelimbs and no hind limbs. Some of their features are primitive while others are derived. Fertilisation is likely to be external as sirenids lack the cloacal glands used by male salamandrids to produce spermatophores and the females lack spermathecae for sperm storage. Despite this, the eggs are laid singly, a behaviour not conducive for external fertilisation. Gymnophiona The order Gymnophiona from the Greek gymnos meaning "naked" and ophis meaning "serpent" or Apoda comprises the caecilians. These are long, cylindrical, limbless animals with a snake or wormlike form. The adults vary in length from 8 to 75 centimetres 3 to 30 inches with the exception of Thomson's caecilian Caecilia thompsoni, which can reach . A caecilian's skin has a large number of transverse folds and in some

species contains tiny embedded dermal scales. It has rudimentary eyes covered in skin, which are probably limited to discerning differences in light intensity. It also has a pair of short tentacles near the eye that can be extended and which have tactile and olfactory functions. Most caecilians live underground in burrows in damp soil, in rotten wood and under plant debris, but some are aquatic. Most species lay their eggs underground and when the larvae hatch, they make their way to adjacent bodies of water. Others brood their eggs and the larvae undergo metamorphosis before the eggs hatch. A few species give birth to live young, nourishing them with glandular secretions while they are in the oviduct. Caecilians have a mostly Gondwanan distribution, being found in tropical regions of Africa, Asia and Central and South America. Anatomy and physiology Skin The integumentary structure contains some typical characteristics common to terrestrial vertebrates, such as the presence of highly cornified outer lay

ers, renewed periodically through a moulting process controlled by the pituitary and thyroid glands. Local thickenings often called warts are common, such as those found on toads. The outside of the skin is shed periodically mostly in one piece, in contrast to mammals and birds where it is shed in flakes. Amphibians often eat the sloughed skin. Caecilians are unique among amphibians in having mineralized dermal scales embedded in the dermis between the furrows in the skin. The similarity of these to the scales of bony fish is largely superficial. Lizards and some frogs have somewhat similar osteoderms forming bony deposits in the dermis, but this is an example of convergent evolution with similar structures having arisen independently in diverse vertebrate lineages. Amphibian skin is permeable to water. Gas exchange can take place through the skin cutaneous respiration and this allows adult amphibians to respire without rising to the surface of water and to hibernate at the bottom of ponds. To compensate for

their thin and delicate skin, amphibians have evolved mucous glands, principally on their heads, backs and tails. The secretions produced by these help keep the skin moist. In addition, most species of amphibian have granular glands that secrete distasteful or poisonous substances. Some amphibian toxins can be lethal to humans while others have little effect. The main poisonproducing glands, the parotoids, produce the neurotoxin bufotoxin and are located behind the ears of toads, along the backs of frogs, behind the eyes of salamanders and on the upper surface of caecilians. The skin colour of amphibians is produced by three layers of pigment cells called chromatophores. These three cell layers consist of the melanophores occupying the deepest layer, the guanophores forming an intermediate layer and containing many granules, producing a bluegreen colour and the lipophores yellow, the most superficial layer. The colour change displayed by many species is initiated by hormones secreted by the pituitary gland.

Unlike bony fish, there is no direct control of the pigment cells by the nervous system, and this results in the colour change taking place more slowly than happens in fish. A vividly coloured skin usually indicates that the species is toxic and is a warning sign to predators. Skeletal system and locomotion Amphibians have a skeletal system that is structurally homologous to other tetrapods, though with a number of variations. They all have four limbs except for the legless caecilians and a few species of salamander with reduced or no limbs. The bones are hollow and lightweight. The musculoskeletal system is strong to enable it to support the head and body. The bones are fully ossified and the vertebrae interlock with each other by means of overlapping processes. The pectoral girdle is supported by muscle, and the welldeveloped pelvic girdle is attached to the backbone by a pair of sacral ribs. The ilium slopes forward and the body is held closer to the ground than is the case in mammals. In most amphibi

ans, there are four digits on the fore foot and five on the hind foot, but no claws on either. Some salamanders have fewer digits and the amphiumas are eellike in appearance with tiny, stubby legs. The sirens are aquatic salamanders with stumpy forelimbs and no hind limbs. The caecilians are limbless. They burrow in the manner of earthworms with zones of muscle contractions moving along the body. On the surface of the ground or in water they move by undulating their body from side to side. In frogs, the hind legs are larger than the fore legs, especially so in those species that principally move by jumping or swimming. In the walkers and runners the hind limbs are not so large, and the burrowers mostly have short limbs and broad bodies. The feet have adaptations for the way of life, with webbing between the toes for swimming, broad adhesive toe pads for climbing, and keratinised tubercles on the hind feet for digging frogs usually dig backwards into the soil. In most salamanders, the limbs are short and more

or less the same length and project at right angles from the body. Locomotion on land is by walking and the tail often swings from side to side or is used as a prop, particularly when climbing. In their normal gait, only one leg is advanced at a time in the manner adopted by their ancestors, the lobefinned fish. Some salamanders in the genus Aneides and certain plethodontids climb trees and have long limbs, large toepads and prehensile tails. In aquatic salamanders and in frog tadpoles, the tail has dorsal and ventral fins and is moved from side to side as a means of propulsion. Adult frogs do not have tails and caecilians have only very short ones. Salamanders use their tails in defence and some are prepared to jettison them to save their lives in a process known as autotomy. Certain species in the Plethodontidae have a weak zone at the base of the tail and use this strategy readily. The tail often continues to twitch after separation which may distract the attacker and allow the salamander to escape. Both

tails and limbs can be regenerated. Adult frogs are unable to regrow limbs but tadpoles can do so. Circulatory system Amphibians have a juvenile stage and an adult stage, and the circulatory systems of the two are distinct. In the juvenile or tadpole stage, the circulation is similar to that of a fish; the twochambered heart pumps the blood through the gills where it is oxygenated, and is spread around the body and back to the heart in a single loop. In the adult stage, amphibians especially frogs lose their gills and develop lungs. They have a heart that consists of a single ventricle and two atria. When the ventricle starts contracting, deoxygenated blood is pumped through the pulmonary artery to the lungs. Continued contraction then pumps oxygenated blood around the rest of the body. Mixing of the two bloodstreams is minimized by the anatomy of the chambers. Nervous and sensory systems The nervous system is basically the same as in other vertebrates, with a central brain, a spinal cord, and nerves th

roughout the body. The amphibian brain is less well developed than that of reptiles, birds and mammals but is similar in morphology and function to that of a fish. It is believed amphibians are capable of perceiving pain. The brain consists of equal parts, cerebrum, midbrain and cerebellum. Various parts of the cerebrum process sensory input, such as smell in the olfactory lobe and sight in the optic lobe, and it is additionally the centre of behaviour and learning. The cerebellum is the center of muscular coordination and the medulla oblongata controls some organ functions including heartbeat and respiration. The brain sends signals through the spinal cord and nerves to regulate activity in the rest of the body. The pineal body, known to regulate sleep patterns in humans, is thought to produce the hormones involved in hibernation and aestivation in amphibians. Tadpoles retain the lateral line system of their ancestral fishes, but this is lost in terrestrial adult amphibians. Some caecilians possess electro

receptors that allow them to locate objects around them when submerged in water. The ears are well developed in frogs. There is no external ear, but the large circular eardrum lies on the surface of the head just behind the eye. This vibrates and sound is transmitted through a single bone, the stapes, to the inner ear. Only highfrequency sounds like mating calls are heard in this way, but lowfrequency noises can be detected through another mechanism. There is a patch of specialized haircells, called papilla amphibiorum, in the inner ear capable of detecting deeper sounds. Another feature, unique to frogs and salamanders, is the columellaoperculum complex adjoining the auditory capsule which is involved in the transmission of both airborne and seismic signals. The ears of salamanders and caecilians are less highly developed than those of frogs as they do not normally communicate with each other through the medium of sound. The eyes of tadpoles lack lids, but at metamorphosis, the cornea becomes more domeshape

d, the lens becomes flatter, and eyelids and associated glands and ducts develop. The adult eyes are an improvement on invertebrate eyes and were a first step in the development of more advanced vertebrate eyes. They allow colour vision and depth of focus. In the retinas are green rods, which are receptive to a wide range of wavelengths. Digestive and excretory systems Many amphibians catch their prey by flicking out an elongated tongue with a sticky tip and drawing it back into the mouth before seizing the item with their jaws. Some use inertial feeding to help them swallow the prey, repeatedly thrusting their head forward sharply causing the food to move backwards in their mouth by inertia. Most amphibians swallow their prey whole without much chewing so they possess voluminous stomachs. The short oesophagus is lined with cilia that help to move the food to the stomach and mucus produced by glands in the mouth and pharynx eases its passage. The enzyme chitinase produced in the stomach helps digest the ch

itinous cuticle of arthropod prey. Amphibians possess a pancreas, liver and gall bladder. The liver is usually large with two lobes. Its size is determined by its function as a glycogen and fat storage unit, and may change with the seasons as these reserves are built or used up. Adipose tissue is another important means of storing energy and this occurs in the abdomen in internal structures called fat bodies, under the skin and, in some salamanders, in the tail. There are two kidneys located dorsally, near the roof of the body cavity. Their job is to filter the blood of metabolic waste and transport the urine via ureters to the urinary bladder where it is stored before being passed out periodically through the cloacal vent. Larvae and most aquatic adult amphibians excrete the nitrogen as ammonia in large quantities of dilute urine, while terrestrial species, with a greater need to conserve water, excrete the less toxic product urea. Some tree frogs with limited access to water excrete most of their metaboli

c waste as uric acid. Respiratory system The lungs in amphibians are primitive compared to those of amniotes, possessing few internal septa and large alveoli, and consequently having a comparatively slow diffusion rate for oxygen entering the blood. Ventilation is accomplished by buccal pumping. Most amphibians, however, are able to exchange gases with the water or air via their skin. To enable sufficient cutaneous respiration, the surface of their highly vascularised skin must remain moist to allow the oxygen to diffuse at a sufficiently high rate. Because oxygen concentration in the water increases at both low temperatures and high flow rates, aquatic amphibians in these situations can rely primarily on cutaneous respiration, as in the Titicaca water frog and the hellbender salamander. In air, where oxygen is more concentrated, some small species can rely solely on cutaneous gas exchange, most famously the plethodontid salamanders, which have neither lungs nor gills. Many aquatic salamanders and all tadp

oles have gills in their larval stage, with some such as the axolotl retaining gills as aquatic adults. Reproduction For the purpose of reproduction most amphibians require fresh water although some lay their eggs on land and have developed various means of keeping them moist. A few e.g. Fejervarya raja can inhabit brackish water, but there are no true marine amphibians. There are reports, however, of particular amphibian populations unexpectedly invading marine waters. Such was the case with the Black Sea invasion of the natural hybrid Pelophylax esculentus reported in 2010. Several hundred frog species in adaptive radiations e.g., Eleutherodactylus, the Pacific Platymantis, the AustraloPapuan microhylids, and many other tropical frogs, however, do not need any water for breeding in the wild. They reproduce via direct development, an ecological and evolutionary adaptation that has allowed them to be completely independent from freestanding water. Almost all of these frogs live in wet tropical rainforests

and their eggs hatch directly into miniature versions of the adult, passing through the tadpole stage within the egg. Reproductive success of many amphibians is dependent not only on the quantity of rainfall, but the seasonal timing. In the tropics, many amphibians breed continuously or at any time of year. In temperate regions, breeding is mostly seasonal, usually in the spring, and is triggered by increasing day length, rising temperatures or rainfall. Experiments have shown the importance of temperature, but the trigger event, especially in arid regions, is often a storm. In anurans, males usually arrive at the breeding sites before females and the vocal chorus they produce may stimulate ovulation in females and the endocrine activity of males that are not yet reproductively active. In caecilians, fertilisation is internal, the male extruding an intromittent organ, the , and inserting it into the female cloaca. The paired Mllerian glands inside the male cloaca secrete a fluid which resembles that produc

ed by mammalian prostate glands and which may transport and nourish the sperm. Fertilisation probably takes place in the oviduct. The majority of salamanders also engage in internal fertilisation. In most of these, the male deposits a spermatophore, a small packet of sperm on top of a gelatinous cone, on the substrate either on land or in the water. The female takes up the sperm packet by grasping it with the lips of the cloaca and pushing it into the vent. The spermatozoa move to the spermatheca in the roof of the cloaca where they remain until ovulation which may be many months later. Courtship rituals and methods of transfer of the spermatophore vary between species. In some, the spermatophore may be placed directly into the female cloaca while in others, the female may be guided to the spermatophore or restrained with an embrace called amplexus. Certain primitive salamanders in the families Sirenidae, Hynobiidae and Cryptobranchidae practice external fertilisation in a similar manner to frogs, with the f

emale laying the eggs in water and the male releasing sperm onto the egg mass. With a few exceptions, frogs use external fertilisation. The male grasps the female tightly with his forelimbs either behind the arms or in front of the back legs, or in the case of Epipedobates tricolor, around the neck. They remain in amplexus with their cloacae positioned close together while the female lays the eggs and the male covers them with sperm. Roughened nuptial pads on the male's hands aid in retaining grip. Often the male collects and retains the egg mass, forming a sort of basket with the hind feet. An exception is the granular poison frog Oophaga granulifera where the male and female place their cloacae in close proximity while facing in opposite directions and then release eggs and sperm simultaneously. The tailed frog Ascaphus truei exhibits internal fertilisation. The "tail" is only possessed by the male and is an extension of the cloaca and used to inseminate the female. This frog lives in fastflowing streams a

nd internal fertilisation prevents the sperm from being washed away before fertilisation occurs. The sperm may be retained in storage tubes attached to the oviduct until the following spring. Most frogs can be classified as either prolonged or explosive breeders. Typically, prolonged breeders congregate at a breeding site, the males usually arriving first, calling and setting up territories. Other satellite males remain quietly nearby, waiting for their opportunity to take over a territory. The females arrive sporadically, mate selection takes place and eggs are laid. The females depart and territories may change hands. More females appear and in due course, the breeding season comes to an end. Explosive breeders on the other hand are found where temporary pools appear in dry regions after rainfall. These frogs are typically fossorial species that emerge after heavy rains and congregate at a breeding site. They are attracted there by the calling of the first male to find a suitable place, perhaps a pool that

forms in the same place each rainy season. The assembled frogs may call in unison and frenzied activity ensues, the males scrambling to mate with the usually smaller number of females. There is a direct competition between males to win the attention of the females in salamanders and newts, with elaborate courtship displays to keep the female's attention long enough to get her interested in choosing him to mate with. Some species store sperm through long breeding seasons, as the extra time may allow for interactions with rival sperm. Life cycle Most amphibians go through metamorphosis, a process of significant morphological change after birth. In typical amphibian development, eggs are laid in water and larvae are adapted to an aquatic lifestyle. Frogs, toads and salamanders all hatch from the egg as larvae with external gills. Metamorphosis in amphibians is regulated by thyroxine concentration in the blood, which stimulates metamorphosis, and prolactin, which counteracts thyroxine's effect. Specific event

s are dependent on threshold values for different tissues. Because most embryonic development is outside the parental body, it is subject to many adaptations due to specific environmental circumstances. For this reason tadpoles can have horny ridges instead of Teeth, whiskerlike skin extensions or fins. They also make use of a sensory lateral line organ similar to that of fish. After metamorphosis, these organs become redundant and will be reabsorbed by controlled cell death, called apoptosis. The variety of adaptations to specific environmental circumstances among amphibians is wide, with many discoveries still being made. Eggs The egg of an amphibian is typically surrounded by a transparent gelatinous covering secreted by the oviducts and containing mucoproteins and mucopolysaccharides. This capsule is permeable to water and gases, and swells considerably as it absorbs water. The ovum is at first rigidly held, but in fertilised eggs the innermost layer liquefies and allows the embryo to move freely. This

also happens in salamander eggs, even when they are unfertilised. Eggs of some salamanders and frogs contain unicellular green algae. These penetrate the jelly envelope after the eggs are laid and may increase the supply of oxygen to the embryo through photosynthesis. They seem to both speed up the development of the larvae and reduce mortality. Most eggs contain the pigment melanin which raises their temperature through the absorption of light and also protects them against ultraviolet radiation. Caecilians, some plethodontid salamanders and certain frogs lay eggs underground that are unpigmented. In the wood frog Rana sylvatica, the interior of the globular egg cluster has been found to be up to warmer than its surroundings, which is an advantage in its cool northern habitat. The eggs may be deposited singly or in small groups, or may take the form of spherical egg masses, rafts or long strings. In terrestrial caecilians, the eggs are laid in grapelike clusters in burrows near streams. The amphibious sal

amander Ensatina attaches its similar clusters by stalks to underwater stems and roots. The greenhouse frog Eleutherodactylus planirostris lays eggs in small groups in the soil where they develop in about two weeks directly into juvenile frogs without an intervening larval stage. The tungara frog Physalaemus pustulosus builds a floating nest from foam to protect its eggs. First a raft is built, then eggs are laid in the centre, and finally a foam cap is overlaid. The foam has antimicrobial properties. It contains no detergents but is created by whipping up proteins and lectins secreted by the female. Larvae The eggs of amphibians are typically laid in water and hatch into freeliving larvae that complete their development in water and later transform into either aquatic or terrestrial adults. In many species of frog and in most lungless salamanders Plethodontidae, direct development takes place, the larvae growing within the eggs and emerging as miniature adults. Many caecilians and some other amphibians la

y their eggs on land, and the newly hatched larvae wriggle or are transported to water bodies. Some caecilians, the alpine salamander Salamandra atra and some of the African livebearing toads Nectophrynoides spp. are viviparous. Their larvae feed on glandular secretions and develop within the female's oviduct, often for long periods. Other amphibians, but not caecilians, are ovoviviparous. The eggs are retained in or on the parent's body, but the larvae subsist on the yolks of their eggs and receive no nourishment from the adult. The larvae emerge at varying stages of their growth, either before or after metamorphosis, according to their species. The toad genus Nectophrynoides exhibits all of these developmental patterns among its dozen or so members. Frogs Frog larvae are known as tadpoles and typically have oval bodies and long, vertically flattened tails with fins. The freeliving larvae are normally fully aquatic, but the tadpoles of some species such as Nannophrys ceylonensis are semiterrestrial and liv

e among wet rocks. Tadpoles have cartilaginous skeletons, gills for respiration external gills at first, internal gills later, lateral line systems and large tails that they use for swimming. Newly hatched tadpoles soon develop gill pouches that cover the gills. The lungs develop early and are used as accessory breathing organs, the tadpoles rising to the water surface to gulp air. Some species complete their development inside the egg and hatch directly into small frogs. These larvae do not have gills but instead have specialised areas of skin through which respiration takes place. While tadpoles do not have true teeth, in most species, the jaws have long, parallel rows of small keratinized structures called keradonts surrounded by a horny beak. Front legs are formed under the gill sac and hind legs become visible a few days later. Iodine and T4 over stimulate the spectacular apoptosis programmed cell death of the cells of the larval gills, tail and fins also stimulate the evolution of nervous systems trans

forming the aquatic, vegetarian tadpole into the terrestrial, carnivorous frog with better neurological, visuospatial, olfactory and cognitive abilities for hunting. In fact, tadpoles developing in ponds and streams are typically herbivorous. Pond tadpoles tend to have deep bodies, large caudal fins and small mouths; they swim in the quiet waters feeding on growing or loose fragments of vegetation. Stream dwellers mostly have larger mouths, shallow bodies and caudal fins; they attach themselves to plants and stones and feed on the surface films of algae and bacteria. They also feed on diatoms, filtered from the water through the gills, and stir up the sediment at bottom of the pond, ingesting edible fragments. They have a relatively long, spiralshaped gut to enable them to digest this diet. Some species are carnivorous at the tadpole stage, eating insects, smaller tadpoles and fish. Young of the Cuban tree frog Osteopilus septentrionalis can occasionally be cannibalistic, the younger tadpoles attacking a lar

ger, more developed tadpole when it is undergoing metamorphosis. At metamorphosis, rapid changes in the body take place as the lifestyle of the frog changes completely. The spiralshaped mouth with horny tooth ridges is reabsorbed together with the spiral gut. The animal develops a large jaw, and its gills disappear along with its gill sac. Eyes and legs grow quickly, and a tongue is formed. There are associated changes in the neural networks such as development of stereoscopic vision and loss of the lateral line system. All this can happen in about a day. A few days later, the tail is reabsorbed, due to the higher thyroxine concentration required for this to take place. Salamanders At hatching, a typical salamander larva has eyes without lids, teeth in both upper and lower jaws, three pairs of feathery external gills, a somewhat laterally flattened body and a long tail with dorsal and ventral fins. The forelimbs may be partially developed and the hind limbs are rudimentary in pondliving species but may be

rather more developed in species that reproduce in moving water. Pondtype larvae often have a pair of balancers, rodlike structures on either side of the head that may prevent the gills from becoming clogged up with sediment. Some members of the genera Ambystoma and Dicamptodon have larvae that never fully develop into the adult form, but this varies with species and with populations. The northwestern salamander Ambystoma gracile is one of these and, depending on environmental factors, either remains permanently in the larval state, a condition known as neoteny, or transforms into an adult. Both of these are able to breed. Neoteny occurs when the animal's growth rate is very low and is usually linked to adverse conditions such as low water temperatures that may change the response of the tissues to the hormone thyroxine. Other factors that may inhibit metamorphosis include lack of food, lack of trace elements and competition from conspecifics. The tiger salamander Ambystoma tigrinum also sometimes behaves in

this way and may grow particularly large in the process. The adult tiger salamander is terrestrial, but the larva is aquatic and able to breed while still in the larval state. When conditions are particularly inhospitable on land, larval breeding may allow continuation of a population that would otherwise die out. There are fifteen species of obligate neotenic salamanders, including species of Necturus, Proteus and Amphiuma, and many examples of facultative ones that adopt this strategy under appropriate environmental circumstances. Lungless salamanders in the family Plethodontidae are terrestrial and lay a small number of unpigmented eggs in a cluster among damp leaf litter. Each egg has a large yolk sac and the larva feeds on this while it develops inside the egg, emerging fully formed as a juvenile salamander. The female salamander often broods the eggs. In the genus Ensatinas, the female has been observed to coil around them and press her throat area against them, effectively massaging them with a mucou

s secretion. In newts and salamanders, metamorphosis is less dramatic than in frogs. This is because the larvae are already carnivorous and continue to feed as predators when they are adults so few changes are needed to their digestive systems. Their lungs are functional early, but the larvae do not make as much use of them as do tadpoles. Their gills are never covered by gill sacs and are reabsorbed just before the animals leave the water. Other changes include the reduction in size or loss of tail fins, the closure of gill slits, thickening of the skin, the development of eyelids, and certain changes in dentition and tongue structure. Salamanders are at their most vulnerable at metamorphosis as swimming speeds are reduced and transforming tails are encumbrances on land. Adult salamanders often have an aquatic phase in spring and summer, and a land phase in winter. For adaptation to a water phase, prolactin is the required hormone, and for adaptation to the land phase, thyroxine. External gills do not retur

n in subsequent aquatic phases because these are completely absorbed upon leaving the water for the first time. Caecilians Most terrestrial caecilians that lay eggs do so in burrows or moist places on land near bodies of water. The development of the young of Ichthyophis glutinosus, a species from Sri Lanka, has been much studied. The eellike larvae hatch out of the eggs and make their way to water. They have three pairs of external red feathery gills, a blunt head with two rudimentary eyes, a lateral line system and a short tail with fins. They swim by undulating their body from side to side. They are mostly active at night, soon lose their gills and make sorties onto land. Metamorphosis is gradual. By the age of about ten months they have developed a pointed head with sensory tentacles near the mouth and lost their eyes, lateral line systems and tails. The skin thickens, embedded scales develop and the body divides into segments. By this time, the caecilian has constructed a burrow and is living on land.

In the majority of species of caecilians, the young are produced by viviparity. Typhlonectes compressicauda, a species from South America, is typical of these. Up to nine larvae can develop in the oviduct at any one time. They are elongated and have paired saclike gills, small eyes and specialised scraping teeth. At first, they feed on the yolks of the eggs, but as this source of nourishment declines they begin to rasp at the ciliated epithelial cells that line the oviduct. This stimulates the secretion of fluids rich in lipids and mucoproteins on which they feed along with scrapings from the oviduct wall. They may increase their length sixfold and be twofifths as long as their mother before being born. By this time they have undergone metamorphosis, lost their eyes and gills, developed a thicker skin and mouth tentacles, and reabsorbed their teeth. A permanent set of teeth grow through soon after birth. The ringed caecilian Siphonops annulatus has developed a unique adaptation for the purposes of reproduc

tion. The progeny feed on a skin layer that is specially developed by the adult in a phenomenon known as maternal dermatophagy. The brood feed as a batch for about seven minutes at intervals of approximately three days which gives the skin an opportunity to regenerate. Meanwhile, they have been observed to ingest fluid exuded from the maternal cloaca. Parental care The care of offspring among amphibians has been little studied but, in general, the larger the number of eggs in a batch, the less likely it is that any degree of parental care takes place. Nevertheless, it is estimated that in up to 20 of amphibian species, one or both adults play some role in the care of the young. Those species that breed in smaller water bodies or other specialised habitats tend to have complex patterns of behaviour in the care of their young. Many woodland salamanders lay clutches of eggs under dead logs or stones on land. The black mountain salamander Desmognathus welteri does this, the mother brooding the eggs and guardi

ng them from predation as the embryos feed on the yolks of their eggs. When fully developed, they break their way out of the egg capsules and disperse as juvenile salamanders. The male hellbender, a primitive salamander, excavates an underwater nest and encourages females to lay there. The male then guards the site for the two or three months before the eggs hatch, using body undulations to fan the eggs and increase their supply of oxygen. The male Colostethus subpunctatus, a tiny frog, protects the egg cluster which is hidden under a stone or log. When the eggs hatch, the male transports the tadpoles on his back, stuck there by a mucous secretion, to a temporary pool where he dips himself into the water and the tadpoles drop off. The male midwife toad Alytes obstetricans winds egg strings round his thighs and carries the eggs around for up to eight weeks. He keeps them moist and when they are ready to hatch, he visits a pond or ditch and releases the tadpoles. The female gastricbrooding frog Rheobatrachus s

pp. reared larvae in her stomach after swallowing either the eggs or hatchlings; however, this stage was never observed before the species became extinct. The tadpoles secrete a hormone that inhibits digestion in the mother whilst they develop by consuming their very large yolk supply. The pouched frog Assa darlingtoni lays eggs on the ground. When they hatch, the male carries the tadpoles around in brood pouches on his hind legs. The aquatic Surinam toad Pipa pipa raises its young in pores on its back where they remain until metamorphosis. The granular poison frog Oophaga granulifera is typical of a number of tree frogs in the poison dart frog family Dendrobatidae. Its eggs are laid on the forest floor and when they hatch, the tadpoles are carried one by one on the back of an adult to a suitable waterfilled crevice such as the axil of a leaf or the rosette of a bromeliad. The female visits the nursery sites regularly and deposits unfertilised eggs in the water and these are consumed by the tadpoles. Genetic

s and genomics Amphibians are notable among vertebrates for their diversity of chromosomes and genomes. The karyotypes chromosomes have been determined for at least 1,193 14.5 of the 8,200 known diploid species, including 963 anurans, 209 salamanders, and 21 caecilians. Generally, the karyotypes of diploid amphibians are characterized by 2026 biarmed chromosomes. Amphibians have also very large genomes compared to other taxa of vertebrates and corresponding variation in genome size Cvalue picograms of DNA in haploid nuclei. The genome sizes range from 0.95 to 11.5 pg in frogs, from 13.89 to 120.56 pg in salamanders, and from 2.94 to 11.78 pg in caecilians. The large genome sizes have prevented wholegenome sequencing of amphibians although a number of genomes have been published recently. The 1.7GB draft genome of Xenopus tropicalis was the first to be reported for amphibians in 2010. Compared to some salamanders this frog genome is tiny. For instance, the genome of the Mexican axolotl turned out to be 32 G

b, which is more than 10 times larger than the human genome 3GB. Feeding and diet With a few exceptions, adult amphibians are predators, feeding on virtually anything that moves that they can swallow. The diet mostly consists of small prey that do not move too fast such as beetles, caterpillars, earthworms and spiders. The sirens Siren spp. often ingest aquatic plant material with the invertebrates on which they feed and a Brazilian tree frog Xenohyla truncata includes a large quantity of fruit in its diet. The Mexican burrowing toad Rhinophrynus dorsalis has a specially adapted tongue for picking up ants and termites. It projects it with the tip foremost whereas other frogs flick out the rear part first, their tongues being hinged at the front. Food is mostly selected by sight, even in conditions of dim light. Movement of the prey triggers a feeding response. Frogs have been caught on fish hooks baited with red flannel and green frogs Rana clamitans have been found with stomachs full of elm seeds that th

ey had seen floating past. Toads, salamanders and caecilians also use smell to detect prey. This response is mostly secondary because salamanders have been observed to remain stationary near odoriferous prey but only feed if it moves. Cavedwelling amphibians normally hunt by smell. Some salamanders seem to have learned to recognize immobile prey when it has no smell, even in complete darkness. Amphibians usually swallow food whole but may chew it lightly first to subdue it. They typically have small hinged pedicellate teeth, a feature unique to amphibians. The base and crown of these are composed of dentine separated by an uncalcified layer and they are replaced at intervals. Salamanders, caecilians and some frogs have one or two rows of teeth in both jaws, but some frogs Rana spp. lack teeth in the lower jaw, and toads Bufo spp. have no teeth. In many amphibians there are also vomerine teeth attached to a facial bone in the roof of the mouth. The tiger salamander Ambystoma tigrinum is typical of the frogs

and salamanders that hide under cover ready to ambush unwary invertebrates. Others amphibians, such as the Bufo spp. toads, actively search for prey, while the Argentine horned frog Ceratophrys ornata lures inquisitive prey closer by raising its hind feet over its back and vibrating its yellow toes. Among leaf litter frogs in Panama, frogs that actively hunt prey have narrow mouths and are slim, often brightly coloured and toxic, while ambushers have wide mouths and are broad and wellcamouflaged. Caecilians do not flick their tongues, but catch their prey by grabbing it with their slightly backwardpointing teeth. The struggles of the prey and further jaw movements work it inwards and the caecilian usually retreats into its burrow. The subdued prey is gulped down whole. When they are newly hatched, frog larvae feed on the yolk of the egg. When this is exhausted some move on to feed on bacteria, algal crusts, detritus and raspings from submerged plants. Water is drawn in through their mouths, which are usually

at the bottom of their heads, and passes through branchial food traps between their mouths and their gills where fine particles are trapped in mucus and filtered out. Others have specialised mouthparts consisting of a horny beak edged by several rows of labial teeth. They scrape and bite food of many kinds as well as stirring up the bottom sediment, filtering out larger particles with the papillae around their mouths. Some, such as the spadefoot toads, have strong biting jaws and are carnivorous or even cannibalistic. Vocalization The calls made by caecilians and salamanders are limited to occasional soft squeaks, grunts or hisses and have not been much studied. A clicking sound sometimes produced by caecilians may be a means of orientation, as in bats, or a form of communication. Most salamanders are considered voiceless, but the California giant salamander Dicamptodon ensatus has vocal cords and can produce a rattling or barking sound. Some species of salamander emit a quiet squeak or yelp if attacked.

Frogs are much more vocal, especially during the breeding season when they use their voices to attract mates. The presence of a particular species in an area may be more easily discerned by its characteristic call than by a fleeting glimpse of the animal itself. In most species, the sound is produced by expelling air from the lungs over the vocal cords into an air sac or sacs in the throat or at the corner of the mouth. This may distend like a balloon and acts as a resonator, helping to transfer the sound to the atmosphere, or the water at times when the animal is submerged. The main vocalisation is the male's loud advertisement call which seeks to both encourage a female to approach and discourage other males from intruding on its territory. This call is modified to a quieter courtship call on the approach of a female or to a more aggressive version if a male intruder draws near. Calling carries the risk of attracting predators and involves the expenditure of much energy. Other calls include those given by

a female in response to the advertisement call and a release call given by a male or female during unwanted attempts at amplexus. When a frog is attacked, a distress or fright call is emitted, often resembling a scream. The usually nocturnal Cuban tree frog Osteopilus septentrionalis produces a rain call when there is rainfall during daylight hours. Territorial behaviour Little is known of the territorial behaviour of caecilians, but some frogs and salamanders defend home ranges. These are usually feeding, breeding or sheltering sites. Males normally exhibit such behaviour though in some species, females and even juveniles are also involved. Although in many frog species, females are larger than males, this is not the case in most species where males are actively involved in territorial defence. Some of these have specific adaptations such as enlarged teeth for biting or spines on the chest, arms or thumbs. In salamanders, defence of a territory involves adopting an aggressive posture and if necessary atta

cking the intruder. This may involve snapping, chasing and sometimes biting, occasionally causing the loss of a tail. The behaviour of red back salamanders Plethodon cinereus has been much studied. 91 of marked individuals that were later recaptured were within a metre yard of their original daytime retreat under a log or rock. A similar proportion, when moved experimentally a distance of , found their way back to their home base. The salamanders left odour marks around their territories which averaged in size and were sometimes inhabited by a male and female pair. These deterred the intrusion of others and delineated the boundaries between neighbouring areas. Much of their behaviour seemed stereotyped and did not involve any actual contact between individuals. An aggressive posture involved raising the body off the ground and glaring at the opponent who often turned away submissively. If the intruder persisted, a biting lunge was usually launched at either the tail region or the nasolabial grooves. Damage t

o either of these areas can reduce the fitness of the rival, either because of the need to regenerate tissue or because it impairs its ability to detect food. In frogs, male territorial behaviour is often observed at breeding locations; calling is both an announcement of ownership of part of this resource and an advertisement call to potential mates. In general, a deeper voice represents a heavier and more powerful individual, and this may be sufficient to prevent intrusion by smaller males. Much energy is used in the vocalization and it takes a toll on the territory holder who may be displaced by a fitter rival if he tires. There is a tendency for males to tolerate the holders of neighbouring territories while vigorously attacking unknown intruders. Holders of territories have a "home advantage" and usually come off better in an encounter between two similarsized frogs. If threats are insufficient, chest to chest tussles may take place. Fighting methods include pushing and shoving, deflating the opponent's

vocal sac, seizing him by the head, jumping on his back, biting, chasing, splashing, and ducking him under the water. Defence mechanisms Amphibians have soft bodies with thin skins, and lack claws, defensive armour, or spines. Nevertheless, they have evolved various defence mechanisms to keep themselves alive. The first line of defence in salamanders and frogs is the mucous secretion that they produce. This keeps their skin moist and makes them slippery and difficult to grip. The secretion is often sticky and distasteful or toxic. Snakes have been observed yawning and gaping when trying to swallow African clawed frogs Xenopus laevis, which gives the frogs an opportunity to escape. Caecilians have been little studied in this respect, but the Cayenne caecilian Typhlonectes compressicauda produces toxic mucus that has killed predatory fish in a feeding experiment in Brazil. In some salamanders, the skin is poisonous. The roughskinned newt Taricha granulosa from North America and other members of its genus con

tain the neurotoxin tetrodotoxin TTX, the most toxic nonprotein substance known and almost identical to that produced by pufferfish. Handling the newts does not cause harm, but ingestion of even the most minute amounts of the skin is deadly. In feeding trials, fish, frogs, reptiles, birds and mammals were all found to be susceptible. The only predators with some tolerance to the poison are certain populations of common garter snake Thamnophis sirtalis. In locations where both snake and salamander coexist, the snakes have developed immunity through genetic changes and they feed on the amphibians with impunity. Coevolution occurs with the newt increasing its toxic capabilities at the same rate as the snake further develops its immunity. Some frogs and toads are toxic, the main poison glands being at the side of the neck and under the warts on the back. These regions are presented to the attacking animal and their secretions may be foultasting or cause various physical or neurological symptoms. Altogether, over

200 toxins have been isolated from the limited number of amphibian species that have been investigated. Poisonous species often use bright colouring to warn potential predators of their toxicity. These warning colours tend to be red or yellow combined with black, with the fire salamander Salamandra salamandra being an example. Once a predator has sampled one of these, it is likely to remember the colouration next time it encounters a similar animal. In some species, such as the firebellied toad Bombina spp., the warning colouration is on the belly and these animals adopt a defensive pose when attacked, exhibiting their bright colours to the predator. The frog Allobates zaparo is not poisonous, but mimics the appearance of other toxic species in its locality, a strategy that may deceive predators. Many amphibians are nocturnal and hide during the day, thereby avoiding diurnal predators that hunt by sight. Other amphibians use camouflage to avoid being detected. They have various colourings such as mottled br

owns, greys and olives to blend into the background. Some salamanders adopt defensive poses when faced by a potential predator such as the North American northern shorttailed shrew Blarina brevicauda. Their bodies writhe and they raise and lash their tails which makes it difficult for the predator to avoid contact with their poisonproducing granular glands. A few salamanders will autotomise their tails when attacked, sacrificing this part of their anatomy to enable them to escape. The tail may have a constriction at its base to allow it to be easily detached. The tail is regenerated later, but the energy cost to the animal of replacing it is significant. Some frogs and toads inflate themselves to make themselves look large and fierce, and some spadefoot toads Pelobates spp scream and leap towards the attacker. Giant salamanders of the genus Andrias, as well as Ceratophrine and Pyxicephalus frogs possess sharp teeth and are capable of drawing blood with a defensive bite. The blackbelly salamander Desmognathus

quadramaculatus can bite an attacking common garter snake Thamnophis sirtalis two or three times its size on the head and often manages to escape. Cognition In amphibians, there is evidence of habituation, associative learning through both classical and instrumental learning, and discrimination abilities. In one experiment, when offered live fruit flies Drosophila virilis, salamanders chose the larger of 1 vs 2 and 2 vs 3. Frogs can distinguish between low numbers 1 vs 2, 2 vs 3, but not 3 vs 4 and large numbers 3 vs 6, 4 vs 8, but not 4 vs 6 of prey. This is irrespective of other characteristics, i.e. surface area, volume, weight and movement, although discrimination among large numbers may be based on surface area. Conservation Dramatic declines in amphibian populations, including population crashes and mass localized extinction, have been noted since the late 1980s from locations all over the world, and amphibian declines are thus perceived to be one of the most critical threats to global biodiversit

y. In 2004, the International Union for Conservation of Nature IUCN reported stating that currently birds, mammals, and amphibians extinction rates were at minimum 48 times greater than natural extinction ratespossibly 1,024 times higher. In 2006, there were believed to be 4,035 species of amphibians that depended on water at some stage during their life cycle. Of these, 1,356 33.6 were considered to be threatened and this figure is likely to be an underestimate because it excludes 1,427 species for which there was insufficient data to assess their status. A number of causes are believed to be involved, including habitat destruction and modification, overexploitation, pollution, introduced species, global warming, endocrinedisrupting pollutants, destruction of the ozone layer ultraviolet radiation has shown to be especially damaging to the skin, eyes, and eggs of amphibians, and diseases like chytridiomycosis. However, many of the causes of amphibian declines are still poorly understood, and are a topic of on

going discussion. With their complex reproductive needs and permeable skins, amphibians are often considered to be ecological indicators. In many terrestrial ecosystems, they constitute one of the largest parts of the vertebrate biomass. Any decline in amphibian numbers will affect the patterns of predation. The loss of carnivorous species near the top of the food chain will upset the delicate ecosystem balance and may cause dramatic increases in opportunistic species. In the Middle East, a growing appetite for eating frog legs and the consequent gathering of them for food was linked to an increase in mosquitoes. Predators that feed on amphibians are affected by their decline. The western terrestrial garter snake Thamnophis elegans in California is largely aquatic and depends heavily on two species of frog that are decreasing in numbers, the Yosemite toad Bufo canorus and the mountain yellowlegged frog Rana muscosa, putting the snake's future at risk. If the snake were to become scarce, this would affect bir

ds of prey and other predators that feed on it. Meanwhile, in the ponds and lakes, fewer frogs means fewer tadpoles. These normally play an important role in controlling the growth of algae and also forage on detritus that accumulates as sediment on the bottom. A reduction in the number of tadpoles may lead to an overgrowth of algae, resulting in depletion of oxygen in the water when the algae later die and decompose. Aquatic invertebrates and fish might then die and there would be unpredictable ecological consequences. A global strategy to stem the crisis was released in 2005 in the form of the Amphibian Conservation Action Plan. Developed by over eighty leading experts in the field, this call to action details what would be required to curtail amphibian declines and extinctions over the following five years and how much this would cost. The Amphibian Specialist Group of the IUCN is spearheading efforts to implement a comprehensive global strategy for amphibian conservation. Amphibian Ark is an organization

that was formed to implement the exsitu conservation recommendations of this plan, and they have been working with zoos and aquaria around the world, encouraging them to create assurance colonies of threatened amphibians. One such project is the Panama Amphibian Rescue and Conservation Project that built on existing conservation efforts in Panama to create a countrywide response to the threat of chytridiomycosis. See also List of amphibians List of amphibian genera List of threatened reptiles and amphibians of the United States References Cited texts Further reading External links Amphibians AnimalSpot.net ArchoZooThque Amphibians skeletons drawings available in vector, image and PDF formats Amphibian Specialist Group Amphibian Ark AmphibiaWeb Global Amphibian Assessment Amphibian vocalisations on Archival Sound Recordings Amphibious organisms Extant Late Devonian first appearances Taxa named by John Edward Gray

Alaska ; ; ; ; Yup'ik Alaskaq; is a state located in the Western United States on the northwest extremity of North America. A semiexclave of the U.S., it borders the Canadian province of British Columbia and the territory of Yukon to the east and shares a maritime border with the Russian Federation's Chukotka Autonomous Okrug to the west, just across the Bering Strait. To the north are the Chukchi and Beaufort seas of the Arctic Ocean, while the Pacific Ocean lies to the south and southwest. Alaska is by far the largest U.S. state by area, comprising more total area than the next three largest states Texas, California, and Montana combined. It represents the seventh largest subnational division in the world. It is the thirdleast populous and the most sparsely populated state, but by far the continent's most populous territory located mostly north of the 60th parallel, with a population of 736,081 as of 2020more than quadruple the combined populations of Northern Canada and Greenland. Approximately half of A

laska's residents live within the Anchorage metropolitan area. The state capital of Juneau is the secondlargest city in the United States by area, comprising more territory than the states of Rhode Island and Delaware. The former capital of Alaska, Sitka, is the largest U.S. city by area. Alaska was occupied by various indigenous peoples for thousands of years before the arrival of Europeans. The state is considered the entry point for the settlement of North America by way of the Bering land bridge. The Russians were the first Europeans to settle the area beginning in the 18th century, eventually establishing Russian America, which spanned most of the current state. The expense and difficulty of maintaining this distant possession prompted its sale to the U.S. in 1867 for US7.2 million equivalent to million in , or approximately two cents per acre 4.74km2. The area went through several administrative changes before becoming organized as a territory on May 11, 1912. It was admitted as the 49th state of the

U.S. on January 3, 1959. While it has one of the smallest state economies in the country, Alaska's per capita income is among the highest, owing to a diversified economy dominated by fishing, natural gas, and oil, all of which it has in abundance. United States armed forces bases and tourism are also a significant part of the economy; more than half the state is federally owned public land, including a multitude of national forests, national parks, and wildlife refuges. The indigenous population of Alaska is proportionally the highest of any U.S. state, at over 15 percent. Close to two dozen native languages are spoken, and Alaskan Natives exercise considerable influence in local and state politics. Etymology The name "Alaska" was introduced in the Russian colonial period when it was used to refer to the Alaska Peninsula. It was derived from an Aleutlanguage idiom, "alaxsxaq", meaning "the mainland" or, more literally, "the object towards which the action of the sea is directed". It is also known as "Al

yeska", the "great land", an Aleut word derived from the same root. History Precolonization Numerous indigenous peoples occupied Alaska for thousands of years before the arrival of European peoples to the area. Linguistic and DNA studies done here have provided evidence for the settlement of North America by way of the Bering land bridge. At the Upward Sun River site in the Tanana Valley in Alaska, remains of a sixweekold infant were found. The baby's DNA showed that she belonged to a population that was genetically separate from other native groups present elsewhere in the New World at the end of the Pleistocene. Ben Potter, the University of Alaska Fairbanks archaeologist who unearthed the remains at the Upward Sun River site in 2013, named this new group Ancient Beringians. The Tlingit people developed a society with a matrilineal kinship system of property inheritance and descent in what is today Southeast Alaska, along with parts of British Columbia and the Yukon. Also in Southeast were the Haida, no

w well known for their unique arts. The Tsimshian people came to Alaska from British Columbia in 1887, when President Grover Cleveland, and later the U.S. Congress, granted them permission to settle on Annette Island and found the town of Metlakatla. All three of these peoples, as well as other indigenous peoples of the Pacific Northwest Coast, experienced smallpox outbreaks from the late 18th through the mid19th century, with the most devastating epidemics occurring in the 1830s and 1860s, resulting in high fatalities and social disruption. The Aleutian Islands are still home to the Aleut people's seafaring society, although they were the first Native Alaskans to be exploited by the Russians. Western and Southwestern Alaska are home to the Yup'ik, while their cousins the Alutiiq Sugpiaq live in what is now Southcentral Alaska. The Gwich'in people of the northern Interior region are Athabaskan and primarily known today for their dependence on the caribou within the muchcontested Arctic National Wildlife Ref

uge. The North Slope and Little Diomede Island are occupied by the widespread Inupiat people. Colonization Some researchers believe the first Russian settlement in Alaska was established in the 17th century. According to this hypothesis, in 1648 several koches of Semyon Dezhnyov's expedition came ashore in Alaska by storm and founded this settlement. This hypothesis is based on the testimony of Chukchi geographer Nikolai Daurkin, who had visited Alaska in 17641765 and who had reported on a village on the Kheuveren River, populated by "bearded men" who "pray to the icons". Some modern researchers associate Kheuveren with Koyuk River. The first European vessel to reach Alaska is generally held to be the St. Gabriel under the authority of the surveyor M. S. Gvozdev and assistant navigator I. Fyodorov on August 21, 1732, during an expedition of Siberian Cossack A. F. Shestakov and Russian explorer Dmitry Pavlutsky 17291735. Another European contact with Alaska occurred in 1741, when Vitus Bering led an expedit

ion for the Russian Navy aboard the St. Peter. After his crew returned to Russia with sea otter pelts judged to be the finest fur in the world, small associations of fur traders began to sail from the shores of Siberia toward the Aleutian Islands. The first permanent European settlement was founded in 1784. Between 1774 and 1800, Spain sent several expeditions to Alaska to assert its claim over the Pacific Northwest. In 1789, a Spanish settlement and fort were built in Nootka Sound. These expeditions gave names to places such as Valdez, Bucareli Sound, and Cordova. Later, the RussianAmerican Company carried out an expanded colonization program during the earlytomid19th century. Sitka, renamed New Archangel from 1804 to 1867, on Baranof Island in the Alexander Archipelago in what is now Southeast Alaska, became the capital of Russian America. It remained the capital after the colony was transferred to the United States. The Russians never fully colonized Alaska, and the colony was never very profitable. Evide

nce of Russian settlement in names and churches survive throughout southeastern Alaska. William H. Seward, the 24th United States Secretary of State, negotiated the Alaska Purchase also known as Seward's Folly with the Russians in 1867 for 7.2 million. Russia's contemporary ruler Tsar Alexander II, the Emperor of the Russian Empire, King of Poland and Grand Duke of Finland, also planned the sale; the purchase was made on March 30, 1867. Six months later the commissioners arrived in Sitka and the formal transfer was arranged; the formal flagraising took place at Fort Sitka on October 18, 1867. In the ceremony 250 uniformed U.S. soldiers marched to the governor's house at "Castle Hill", where the Russian troops lowered the Russian flag and the U.S. flag was raised. This event is celebrated as Alaska Day, a legal holiday on October 18. Alaska was loosely governed by the military initially, and was administered as a district starting in 1884, with a governor appointed by the United States president. A federal d

istrict court was headquartered in Sitka. For most of Alaska's first decade under the United States flag, Sitka was the only community inhabited by American settlers. They organized a "provisional city government", which was Alaska's first municipal government, but not in a legal sense. Legislation allowing Alaskan communities to legally incorporate as cities did not come about until 1900, and home rule for cities was extremely limited or unavailable until statehood took effect in 1959. Alaska as an incorporated U.S. territory Starting in the 1890s and stretching in some places to the early 1910s, gold rushes in Alaska and the nearby Yukon Territory brought thousands of miners and settlers to Alaska. Alaska was officially incorporated as an organized territory in 1912. Alaska's capital, which had been in Sitka until 1906, was moved north to Juneau. Construction of the Alaska Governor's Mansion began that same year. European immigrants from Norway and Sweden also settled in southeast Alaska, where they enter

ed the fishing and logging industries. During World War II, the Aleutian Islands Campaign focused on Attu, Agattu and Kiska, all which were occupied by the Empire of Japan. During the Japanese occupation, a white American civilian and two United States Navy personnel were killed at Attu and Kiska respectively, and nearly a total of 50 Aleut civilians and eight sailors were interned in Japan. About half of the Aleuts died during the period of internment. UnalaskaDutch Harbor and Adak became significant bases for the United States Army, United States Army Air Forces and United States Navy. The United States LendLease program involved flying American warplanes through Canada to Fairbanks and then Nome; Soviet pilots took possession of these aircraft, ferrying them to fight the German invasion of the Soviet Union. The construction of military bases contributed to the population growth of some Alaskan cities. Statehood Statehood for Alaska was an important cause of James Wickersham early in his tenure as a cong

ressional delegate. Decades later, the statehood movement gained its first real momentum following a territorial referendum in 1946. The Alaska Statehood Committee and Alaska's Constitutional Convention would soon follow. Statehood supporters also found themselves fighting major battles against political foes, mostly in the U.S. Congress but also within Alaska. Statehood was approved by the U.S. Congress on July 7, 1958; Alaska was officially proclaimed a state on January 3, 1959. Good Friday earthquake On March 27, 1964, the massive Good Friday earthquake killed 133 people and destroyed several villages and portions of large coastal communities, mainly by the resultant tsunamis and landslides. It was the secondmostpowerful earthquake in recorded history, with a moment magnitude of 9.2 more than a thousand times as powerful as the 1989 San Francisco earthquake. The time of day 536 pm, time of year spring and location of the epicenter were all cited as factors in potentially sparing thousands of lives, parti

cularly in Anchorage. Alaska oil boom The 1968 discovery of oil at Prudhoe Bay and the 1977 completion of the TransAlaska Pipeline System led to an oil boom. Royalty revenues from oil have funded large state budgets from 1980 onward. That same year, not coincidentally, Alaska repealed its state income tax. In 1989, the Exxon Valdez hit a reef in the Prince William Sound, spilling more than of crude oil over of coastline. Today, the battle between philosophies of development and conservation is seen in the contentious debate over oil drilling in the Arctic National Wildlife Refuge and the proposed Pebble Mine. Geography Located at the northwest corner of North America, Alaska is the northernmost and westernmost state in the United States, but also has the most easterly longitude in the United States because the Aleutian Islands extend into the Eastern Hemisphere. Alaska is the only noncontiguous U.S. state on continental North America; about of British Columbia Canada separates Alaska from Washington.

It is technically part of the continental U.S., but is sometimes not included in colloquial use; Alaska is not part of the contiguous U.S., often called "the Lower 48". The capital city, Juneau, is situated on the mainland of the North American continent but is not connected by road to the rest of the North American highway system. The state is bordered by Canada's Yukon and British Columbia to the east making it the only state to border a Canadian territory; the Gulf of Alaska and the Pacific Ocean to the south and southwest; the Bering Sea, Bering Strait, and Chukchi Sea to the west; and the Arctic Ocean to the north. Alaska's territorial waters touch Russia's territorial waters in the Bering Strait, as the Russian Big Diomede Island and Alaskan Little Diomede Island are only apart. Alaska has a longer coastline than all the other U.S. states combined. At in area, Alaska is by far the largest state in the United States, and is more than twice the size of the secondlargest U.S. state, Texas. Alaska is t

he seventh largest subnational division in the world, and if it was an independent nation would be the 16th largest country in the world, as it is larger than Iran. With its myriad islands, Alaska has nearly of tidal shoreline. The Aleutian Islands chain extends west from the southern tip of the Alaska Peninsula. Many active volcanoes are found in the Aleutians and in coastal regions. Unimak Island, for example, is home to Mount Shishaldin, which is an occasionally smoldering volcano that rises to above the North Pacific. The chain of volcanoes extends to Mount Spurr, west of Anchorage on the mainland. Geologists have identified Alaska as part of Wrangellia, a large region consisting of multiple states and Canadian provinces in the Pacific Northwest, which is actively undergoing continent building. One of the world's largest tides occurs in Turnagain Arm, just south of Anchorage, where tidal differences can be more than . Alaska has more than three million lakes. Marshlands and wetland permafrost cover

mostly in northern, western and southwest flatlands. Glacier ice covers about of Alaska. The Bering Glacier is the largest glacier in North America, covering alone. Regions There are no officially defined borders demarcating the various regions of Alaska, but there are six widely accepted regions South Central The most populous region of Alaska, containing Anchorage, the MatanuskaSusitna Valley and the Kenai Peninsula. Rural, mostly unpopulated areas south of the Alaska Range and west of the Wrangell Mountains also fall within the definition of South Central, as do the Prince William Sound area and the communities of Cordova and Valdez. Southeast Also referred to as the Panhandle or Inside Passage, this is the region of Alaska closest to the contiguous states. As such, this was where most of the initial nonindigenous settlement occurred in the years following the Alaska Purchase. The region is dominated by the Alexander Archipelago as well as the Tongass National Forest, the largest national forest in

the United States. It contains the state capital Juneau, the former capital Sitka, and Ketchikan, at one time Alaska's largest city. The Alaska Marine Highway provides a vital surface transportation link throughout the area and country, as only three communities Haines, Hyder and Skagway enjoy direct connections to the contiguous North American road system. Interior The Interior is the largest region of Alaska; much of it is uninhabited wilderness. Fairbanks is the only large city in the region. Denali National Park and Preserve is located here. Denali, formerly Mount McKinley, is the highest mountain in North America, and is also located here. Southwest Southwest Alaska is a sparsely inhabited region stretching some inland from the Bering Sea. Most of the population lives along the coast. Kodiak Island is also located in Southwest. The massive YukonKuskokwim Delta, one of the largest river deltas in the world, is here. Portions of the Alaska Peninsula are considered part of Southwest, with the remainin

g portions included with the Aleutian Islands see below. North Slope The North Slope is mostly tundra peppered with small villages. The area is known for its massive reserves of crude oil and contains both the National Petroleum ReserveAlaska and the Prudhoe Bay Oil Field. The city of Utqiavik, formerly known as Barrow, is the northernmost city in the United States and is located here. The Northwest Arctic area, anchored by Kotzebue and also containing the Kobuk River valley, is often regarded as being part of this region. However, the respective Inupiat of the North Slope and of the Northwest Arctic seldom consider themselves to be one people. Aleutian Islands More than 300 small volcanic islands make up this chain, which stretches more than into the Pacific Ocean. Some of these islands fall in the Eastern Hemisphere, but the International Date Line was drawn west of 180 to keep the whole state, and thus the entire North American continent, within the same legal day. Two of the islands, Attu and Kiska,

were occupied by Japanese forces during World War II. Land ownership According to an October 1998 report by the United States Bureau of Land Management, approximately 65 of Alaska is owned and managed by the U.S. federal government as public lands, including a multitude of national forests, national parks, and national wildlife refuges. Of these, the Bureau of Land Management manages , or 23.8 of the state. The Arctic National Wildlife Refuge is managed by the United States Fish and Wildlife Service. It is the world's largest wildlife refuge, comprising . Of the remaining land area, the state of Alaska owns , its entitlement under the Alaska Statehood Act. A portion of that acreage is occasionally ceded to the organized boroughs presented above, under the statutory provisions pertaining to newly formed boroughs. Smaller portions are set aside for rural subdivisions and other homesteadingrelated opportunities. These are not very popular due to the often remote and roadless locations. The University of Alask

a, as a land grant university, also owns substantial acreage which it manages independently. Another are owned by 12 regional, and scores of local, Native corporations created under the Alaska Native Claims Settlement Act ANCSA of 1971. Regional Native corporation Doyon, Limited often promotes itself as the largest private landowner in Alaska in advertisements and other communications. Provisions of ANCSA allowing the corporations' land holdings to be sold on the open market starting in 1991 were repealed before they could take effect. Effectively, the corporations hold title including subsurface title in many cases, a privilege denied to individual Alaskans but cannot sell the land. Individual Native allotments can be and are sold on the open market, however. Various private interests own the remaining land, totaling about one percent of the state. Alaska is, by a large margin, the state with the smallest percentage of private land ownership when Native corporation holdings are excluded. Alaska Heritage

Resources Survey The Alaska Heritage Resources Survey AHRS is a restricted inventory of all reported historic and prehistoric sites within the U.S. state of Alaska; it is maintained by the Office of History and Archaeology. The survey's inventory of cultural resources includes objects, structures, buildings, sites, districts, and travel ways, with a general provision that they are more than fifty years old. , more than 35,000 sites have been reported. Cities, towns and boroughs Alaska is not divided into counties, as most of the other U.S. states, but it is divided into boroughs. Delegates to the Alaska Constitutional Convention wanted to avoid the pitfalls of the traditional county system and adopted their own unique model. Many of the more densely populated parts of the state are part of Alaska's 16 boroughs, which function somewhat similarly to counties in other states. However, unlike countyequivalents in the other 49 states, the boroughs do not cover the entire land area of the state. The area not par

t of any borough is referred to as the Unorganized Borough. The Unorganized Borough has no government of its own, but the U.S. Census Bureau in cooperation with the state divided the Unorganized Borough into 11 census areas solely for the purposes of statistical analysis and presentation. A recording district is a mechanism for management of the public record in Alaska. The state is divided into 34 recording districts which are centrally administered under a state recorder. All recording districts use the same acceptance criteria, fee schedule, etc., for accepting documents into the public record. Whereas many U.S. states use a threetiered system of decentralizationstatecountytownshipmost of Alaska uses only two tiersstateborough. Owing to the low population density, most of the land is located in the Unorganized Borough. As the name implies, it has no intermediate borough government but is administered directly by the state government. In 2000, 57.71 of Alaska's area has this status, with 13.05 of the popu

lation. Anchorage merged the city government with the Greater Anchorage Area Borough in 1975 to form the Municipality of Anchorage, containing the city proper and the communities of Eagle River, Chugiak, Peters Creek, Girdwood, Bird, and Indian. Fairbanks has a separate borough the Fairbanks North Star Borough and municipality the City of Fairbanks. The state's most populous city is Anchorage, home to 291,247 people in 2020. The richest location in Alaska by per capita income is Denali 42,245. Yakutat City, Sitka, Juneau, and Anchorage are the four largest cities in the U.S. by area. Cities and censusdesignated places by population As reflected in the 2020 United States census, Alaska has a total of 355 incorporated cities and censusdesignated places CDPs. The tally of cities includes four unified municipalities, essentially the equivalent of a consolidated citycounty. The majority of these communities are located in the rural expanse of Alaska known as "The Bush" and are unconnected to the contiguous Nor

th American road network. The table at the bottom of this section lists the 100 largest cities and censusdesignated places in Alaska, in population order. Of Alaska's 2020 U.S. census population figure of 733,391, 16,655 people, or 2.27 of the population, did not live in an incorporated city or censusdesignated place. Approximately threequarters of that figure were people who live in urban and suburban neighborhoods on the outskirts of the city limits of Ketchikan, Kodiak, Palmer and Wasilla. CDPs have not been established for these areas by the United States Census Bureau, except that seven CDPs were established for the Ketchikanarea neighborhoods in the 1980 Census Clover Pass, Herring Cove, Ketchikan East, Mountain Point, North Tongass Highway, Pennock Island and Saxman East, but have not been used since. The remaining population was scattered throughout Alaska, both within organized boroughs and in the Unorganized Borough, in largely remote areas. Climate The climate in south and southeastern Alaska is

a midlatitude oceanic climate Kppen climate classification Cfb, and a subarctic oceanic climate Kppen Cfc in the northern parts. On an annual basis, the southeast is both the wettest and warmest part of Alaska with milder temperatures in the winter and high precipitation throughout the year. Juneau averages over of precipitation a year, and Ketchikan averages over . This is also the only region in Alaska in which the average daytime high temperature is above freezing during the winter months.The climate of Anchorage and south central Alaska is mild by Alaskan standards due to the region's proximity to the seacoast. While the area gets less rain than southeast Alaska, it gets more snow, and days tend to be clearer. On average, Anchorage receives of precipitation a year, with around of snow, although there are areas in the south central which receive far more snow. It is a subarctic climate Kppen Dfc due to its brief, cool summers. The climate of western Alaska is determined in large part by the Bering Sea

and the Gulf of Alaska. It is a subarctic oceanic climate in the southwest and a continental subarctic climate farther north. The temperature is somewhat moderate considering how far north the area is. This region has a tremendous amount of variety in precipitation. An area stretching from the northern side of the Seward Peninsula to the Kobuk River valley i.e., the region around Kotzebue Sound is technically a desert, with portions receiving less than of precipitation annually. On the other extreme, some locations between Dillingham and Bethel average around of precipitation. The climate of the interior of Alaska is subarctic. Some of the highest and lowest temperatures in Alaska occur around the area near Fairbanks. The summers may have temperatures reaching into the 90s F the lowtomid 30s C, while in the winter, the temperature can fall below . Precipitation is sparse in the Interior, often less than a year, but what precipitation falls in the winter tends to stay the entire winter. The highest and l

owest recorded temperatures in Alaska are both in the Interior. The highest is in Fort Yukon which is just inside the arctic circle on June 27, 1915, making Alaska tied with Hawaii as the state with the lowest high temperature in the United States. The lowest official Alaska temperature is in Prospect Creek on January 23, 1971, one degree above the lowest temperature recorded in continental North America in Snag, Yukon, Canada. The climate in the extreme north of Alaska is Arctic Kppen ET with long, very cold winters and short, cool summers. Even in July, the average low temperature in Utqiavik is . Precipitation is light in this part of Alaska, with many places averaging less than per year, mostly as snow which stays on the ground almost the entire year. Demographics The United States Census Bureau found in the 2020 United States census that the population of Alaska was 736,081 on April 1, 2020, a 3.6 increase since the 2010 United States census. According to the 2010 United States census, the U.S. st

ate of Alaska had a population of 710,231, increasing from 626,932 at the 2000 U.S. census. In 2010, Alaska ranked as the 47th state by population, ahead of North Dakota, Vermont, and Wyoming and Washington, D.C.. Estimates show North Dakota ahead . Alaska is the least densely populated state, and one of the most sparsely populated areas in the world, at , with the next state, Wyoming, at . Alaska is by far the largest U.S. state by area, and the tenth wealthiest per capita income. due to its population size, it is one of 14 U.S. states that still have only one telephone area code. Race and ethnicity The 2019 American Community Survey estimated 60.2 of the population was nonHispanic white, 3.7 Black or African American, 15.6 American Indian or Alaska Native, 6.5 Asian, 1.4 Native Hawaiian and other Pacific Islander, 7.5 two or more races, and 7.3 Hispanic or Latin American of any race. At the survey estimates, 7.8 of the total population was foreignborn from 2015 to 2019. In 2015, 61.3 was nonHispanic whi

te, 3.4 Black or African American, 13.3 American Indian or Alaska Native, 6.2 Asian, 0.9 Native Hawaiian and other Pacific Islander, 0.3 some other race, and 7.7 multiracial. Hispanics and Latin Americans were 7 of the state population in 2015. From 2015 to 2019, the largest Hispanic and Latin American groups were Mexican Americans, Puerto Ricans, and Cuban Americans. The largest Asian groups living in the state were Filipinos, Korean Americans, and Japanese and Chinese Americans. The state was 66.7 White 64.1 nonHispanic white, 14.8 American Indian and Alaska Native, 5.4 Asian, 3.3 Black or African American, 1.0 Native Hawaiian and other Pacific Islander, 1.6 from some other race, and 7.3 from two or more races in 2010. Hispanics or Latin Americans of any race made up 5.5 of the population in 2010. , 50.7 of Alaska's population younger than one year of age belonged to minority groups i.e., did not have two parents of nonHispanic white ancestry. In 1960, the United States Census Bureau reported Alaska's popu

lation as 77.2 White, 3 Black, and 18.8 American Indian and Alaska Native. Languages According to the 2011 American Community Survey, 83.4 of people over the age of five spoke only English at home. About 3.5 spoke Spanish at home, 2.2 spoke another IndoEuropean language, about 4.3 spoke an Asian language including Tagalog, and about 5.3 spoke other languages at home. In 2019, the American Community Survey determined 83.7 spoke only English, and 16.3 spoke another language other than English. The most spoken European language after English was Spanish, spoken by approximately 4.0 of the state population. Collectively, Asian and Pacific Islander languages were spoken by 5.6 of Alaskans. Since 2010, a total of 5.2 of Alaskans speak one of the state's 20 indigenous languages, known locally as "native languages". The Alaska Native Language Center at the University of Alaska Fairbanks claims that at least 20 Alaskan native languages exist and there are also some languages with different dialects. Most of Alaska'

s native languages belong to either the EskimoAleut or NaDene language families; however, some languages are thought to be isolates e.g. Haida or have not yet been classified e.g. Tsimshianic. nearly all of Alaska's native languages were classified as either threatened, shifting, moribund, nearly extinct, or dormant languages. In October 2014, the governor of Alaska signed a bill declaring the state's 20 indigenous languages to have official status. This bill gave them symbolic recognition as official languages, though they have not been adopted for official use within the government. The 20 languages that were included in the bill are Inupiaq Siberian Yupik Central Alaskan Yup'ik Alutiiq Unangax Dena'ina Deg Xinag Holikachuk Koyukon Upper Kuskokwim Gwich'in Tanana Upper Tanana Tanacross Hn Ahtna Eyak Tlingit Haida Tsimshian Religion According to statistics collected by the Association of Religion Data Archives from 2010, about 34 of Alaska residents were members of religious congrega

tions. Of the religious population, 100,960 people identified as evangelical Protestants; 50,866 as Roman Catholic; and 32,550 as mainline Protestants. Roughly 4 were Mormon, 0.5 Jewish, 0.5 Muslim, 1 Buddhist, 0.2 Bah, and 0.5 Hindu. The largest religious denominations in Alaska was the Catholic Church with 50,866 adherents; nondenominational Evangelicals with 38,070 adherents; The Church of Jesus Christ of Latterday Saints with 32,170 adherents; and the Southern Baptist Convention with 19,891 adherents. Alaska has been identified, along with Pacific Northwest states Washington and Oregon, as being the least religious states of the USA, in terms of church membership. The Pew Research Center in 2014 determined 62 of the adult population practiced Christianity. Protestantism was the largest Christian tradition, dominated by Evangelicalism. Mainline Protestants were the second largest Protestant Christian group, followed by predominantly African American churches. The Catholic Church remained the largest sing

le Christian tradition practiced in Alaska. Of the unaffiliated population, they made up the largest nonChristian religious affiliation. Atheists made up 5 of the population and the largest nonChristian religion was Buddhism. In 1795, the first Russian Orthodox Church was established in Kodiak. Intermarriage with Alaskan Natives helped the Russian immigrants integrate into society. As a result, an increasing number of Russian Orthodox churches gradually became established within Alaska. Alaska also has the largest Quaker population by percentage of any state. In 2009, there were 6,000 Jews in Alaska for whom observance of halakha may pose special problems. Alaskan Hindus often share venues and celebrations with members of other Asian religious communities, including Sikhs and Jains. In 2010, Alaskan Hindus established the Sri Ganesha Temple of Alaska, making it the first Hindu Temple in Alaska and the northernmost Hindu Temple in the world. There are an estimated 2,0003,000 Hindus in Alaska. The vast majorit

y of Hindus live in Anchorage or Fairbanks. Estimates for the number of Muslims in Alaska range from 2,000 to 5,000. The Islamic Community Center of Anchorage began efforts in the late 1990s to construct a mosque in Anchorage. They broke ground on a building in south Anchorage in 2010 and were nearing completion in late 2014. When completed, the mosque will be the first in the state and one of the northernmost mosques in the world. There's also a Bah center. Economy As of 2016, Alaska had a total employment of 266,072. The number of employer establishments was 21,077. The 2018 gross state product was 55 billion, 48th in the U.S.. Its per capita personal income for 2018 was 73,000, ranking 7th in the nation. According to a 2013 study by Phoenix Marketing International, Alaska had the fifthlargest number of millionaires per capita in the United States, with a ratio of 6.75 percent. The oil and gas industry dominates the Alaskan economy, with more than 80 of the state's revenues derived from petroleum extrac

tion. Alaska's main export product excluding oil and natural gas is seafood, primarily salmon, cod, Pollock and crab. Agriculture represents a very small fraction of the Alaskan economy. Agricultural production is primarily for consumption within the state and includes nursery stock, dairy products, vegetables, and livestock. Manufacturing is limited, with most foodstuffs and general goods imported from elsewhere. Employment is primarily in government and industries such as natural resource extraction, shipping, and transportation. Military bases are a significant component of the economy in the Fairbanks North Star, Anchorage and Kodiak Island boroughs, as well as Kodiak. Federal subsidies are also an important part of the economy, allowing the state to keep taxes low. Its industrial outputs are crude petroleum, natural gas, coal, gold, precious metals, zinc and other mining, seafood processing, timber and wood products. There is also a growing service and tourism sector. Tourists have contributed to the e

conomy by supporting local lodging. Energy Alaska has vast energy resources, although its oil reserves have been largely depleted. Major oil and gas reserves were found in the Alaska North Slope ANS and Cook Inlet basins, but according to the Energy Information Administration, by February 2014 Alaska had fallen to fourth place in the nation in crude oil production after Texas, North Dakota, and California. Prudhoe Bay on Alaska's North Slope is still the second highestyielding oil field in the United States, typically producing about , although by early 2014 North Dakota's Bakken Formation was producing over . Prudhoe Bay was the largest conventional oil field ever discovered in North America, but was much smaller than Canada's enormous Athabasca oil sands field, which by 2014 was producing about of unconventional oil, and had hundreds of years of producible reserves at that rate. The TransAlaska Pipeline can transport and pump up to of crude oil per day, more than any other crude oil pipeline in the Uni

ted States. Additionally, substantial coal deposits are found in Alaska's bituminous, subbituminous, and lignite coal basins. The United States Geological Survey estimates that there are of undiscovered, technically recoverable gas from natural gas hydrates on the Alaskan North Slope. Alaska also offers some of the highest hydroelectric power potential in the country from its numerous rivers. Large swaths of the Alaskan coastline offer wind and geothermal energy potential as well. Alaska's economy depends heavily on increasingly expensive diesel fuel for heating, transportation, electric power and light. Although wind and hydroelectric power are abundant and underdeveloped, proposals for statewide energy systems e.g. with special lowcost electric interties were judged uneconomical at the time of the report, 2001 due to low less than 50gal fuel prices, long distances and low population. The cost of a gallon of gas in urban Alaska today is usually thirty to sixty cents higher than the national average; prices

in rural areas are generally significantly higher but vary widely depending on transportation costs, seasonal usage peaks, nearby petroleum development infrastructure and many other factors. Permanent Fund The Alaska Permanent Fund is a constitutionally authorized appropriation of oil revenues, established by voters in 1976 to manage a surplus in state petroleum revenues from oil, largely in anticipation of the then recently constructed TransAlaska Pipeline System. The fund was originally proposed by Governor Keith Miller on the eve of the 1969 Prudhoe Bay lease sale, out of fear that the legislature would spend the entire proceeds of the sale which amounted to 900 million at once. It was later championed by Governor Jay Hammond and Kenai state representative Hugh Malone. It has served as an attractive political prospect ever since, diverting revenues which would normally be deposited into the general fund. The Alaska Constitution was written so as to discourage dedicating state funds for a particular pur

pose. The Permanent Fund has become the rare exception to this, mostly due to the political climate of distrust existing during the time of its creation. From its initial principal of 734,000, the fund has grown to 50 billion as a result of oil royalties and capital investment programs. Most if not all the principal is invested conservatively outside Alaska. This has led to frequent calls by Alaskan politicians for the Fund to make investments within Alaska, though such a stance has never gained momentum. Starting in 1982, dividends from the fund's annual growth have been paid out each year to eligible Alaskans, ranging from an initial 1,000 in 1982 equal to three years' payout, as the distribution of payments was held up in a lawsuit over the distribution scheme to 3,269 in 2008 which included a onetime 1,200 "Resource Rebate". Every year, the state legislature takes out 8 from the earnings, puts 3 back into the principal for inflation proofing, and the remaining 5 is distributed to all qualifying Alaskans.

To qualify for the Permanent Fund Dividend, one must have lived in the state for a minimum of 12 months, maintain constant residency subject to allowable absences, and not be subject to court judgments or criminal convictions which fall under various disqualifying classifications or may subject the payment amount to civil garnishment. The Permanent Fund is often considered to be one of the leading examples of a basic income policy in the world. Cost of living The cost of goods in Alaska has long been higher than in the contiguous 48 states. Federal government employees, particularly United States Postal Service USPS workers and activeduty military members, receive a Cost of Living Allowance usually set at 25 of base pay because, while the cost of living has gone down, it is still one of the highest in the country. Rural Alaska suffers from extremely high prices for food and consumer goods compared to the rest of the country, due to the relatively limited transportation infrastructure. Agriculture and fi

shing Due to the northern climate and short growing season, relatively little farming occurs in Alaska. Most farms are in either the Matanuska Valley, about northeast of Anchorage, or on the Kenai Peninsula, about southwest of Anchorage. The short 100day growing season limits the crops that can be grown, but the long sunny summer days make for productive growing seasons. The primary crops are potatoes, carrots, lettuce, and cabbage. The Tanana Valley is another notable agricultural locus, especially the Delta Junction area, about southeast of Fairbanks, with a sizable concentration of farms growing agronomic crops; these farms mostly lie north and east of Fort Greely. This area was largely set aside and developed under a state program spearheaded by Hammond during his second term as governor. Deltaarea crops consist predominantly of barley and hay. West of Fairbanks lies another concentration of small farms catering to restaurants, the hotel and tourist industry, and communitysupported agriculture. Alas