Frog

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For other uses, see Frog (disambiguation).

Frogs Temporal range: Triassic–present PreЄ Є O S D C P T J K Pg N
Australian Green Tree Frog (Litoria caerulea)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Amphibia
Subclass:	Lissamphibia
Order:	Anura Merrem, 1820
Suborders
Archaeobatrachia Mesobatrachia Neobatrachia - List of Anuran families
Native distribution of frogs (in black)

Frogs are amphibians in the order Anura (meaning "tail-less", from Greek an-, without + oura, tail), formerly referred to as Salientia (Latin salere (salio), "to jump"). Most frogs are characterized by a short body, webbed digits (fingers or toes), protruding eyes and the absence of a tail. Frogs are widely known as exceptional jumpers, and many of the anatomical characteristics of frogs, particularly their long, powerful legs, are adaptations to improve jumping performance. Due to their permeable skin, frogs are often semi-aquatic or inhabit humid areas, but move easily on land. They typically lay their eggs in puddles, ponds or lakes, and their larvae, called tadpoles, have gills and develop in water. Adult frogs follow a carnivorous diet, mostly of arthropods, annelids and gastropods. Frogs are most noticeable by their call, which can be widely heard during the night or day, mainly in their mating season.
The distribution of frogs ranges from tropic to subarctic regions, but most species are found in tropical rainforests. Consisting of more than 5,000 species described, they are among the most diverse groups of vertebrates. However, populations of certain frog species are declining significantly.
A popular distinction is often made between frogs and toads on the basis of their appearance, but this has no taxonomic basis. (Members of the anuran family Bufonidae are called true toads, but many species from other families are also called toads.) In addition to their ecological importance, frogs have many cultural roles, such as in literature, symbolism and religion, and they are also valued as food and as pets.

Contents [hide] 1 Etymology and terminology 2 Taxonomy 3 Morphology and physiology 3.1 Feet and legs 3.2 Jumping 3.3 Skin 3.4 Poison 3.5 Respiration and circulation 3.6 Digestion and excretion 3.7 Nervous system 4 Natural history 4.1 Life cycle 4.2 Reproduction of frogs 4.3 Parental care 4.4 Call 5 Distribution and conservation status 6 Evolution 7 Uses in agriculture and research 8 Cultural beliefs 9 See also 10 References 10.1 Notes 10.2 Bibliography 11 External links

Etymology and terminology

The name frog derives from Old English frogga, (compare Old Norse frauki, German Frosch, older Dutch spelling kikvorsch), cognate with Sanskrit plava (frog), probably deriving from Proto-Indo-European praw = "to jump".^[1]
A distinction is often made between frogs and toads on the basis of their appearance, caused by the convergent adaptation among so-called toads to dry environments; however, this distinction has no taxonomic basis. The only family exclusively given the common name "toad" is Bufonidae, but many species from other families are also called "toads," and the species within the toad genus Atelopus are referred to as "harlequin frogs".

Taxonomy

For more details on this topic, see List of Anuran families.

The order Anura contains 4,810 species^[2] in 33 families, of which the Leptodactylidae (1100 spp.), Hylidae (800 spp.) and Ranidae (750 spp.) are the richest in species. About 88% of amphibian species are frogs.

European Fire-bellied Toad (Bombina bombina)

Young American bullfrog found in a stream in New Jersey

The use of the common names "frog" and "toad" has no taxonomic justification. From a taxonomic perspective, all members of the order Anura are frogs, but only members of the family Bufonidae are considered "true toads". The use of the term "frog" in common names usually refers to species that are aquatic or semi-aquatic with smooth and/or moist skins, and the term "toad" generally refers to species that tend to be terrestrial with dry, warty skin. An exception is the fire-bellied toad (Bombina bombina): while its skin is slightly warty, it prefers a watery habitat.
Frogs and toads are broadly classified into three suborders: Archaeobatrachia, which includes four families of primitive frogs; Mesobatrachia, which includes five families of more evolutionary intermediate frogs; and Neobatrachia, by far the largest group, which contains the remaining 24 families of "modern" frogs, including most common species throughout the world. Neobatrachia is further divided into the Hyloidea and Ranoidea.^[3] This classification is based on such morphological features as the number of vertebrae, the structure of the pectoral girdle, and the morphology of tadpoles. While this classification is largely accepted, relationships among families of frogs are still debated. Future studies of molecular genetics should soon provide further insights to the evolutionary relationships among anuran families.^[4]
Some species of anurans hybridise readily. For instance, the Edible Frog (Rana esculenta) is a hybrid of the Pool Frog (R. lessonae) and the Marsh Frog (R. ridibunda). Bombina bombina and Bombina variegata similarly form hybrids, although these are less fertile, giving rise to a hybrid zone.

Morphology and physiology

Skeleton of Rana

The morphology of frogs is unique among amphibians. Compared with the other two groups of amphibians, (salamanders and caecilians), frogs are unusual because they lack tails as adults and their legs are more suited to jumping than walking. The physiology of frogs is generally like that of other amphibians (and differs from other terrestrial vertebrates) because oxygen can pass through their highly permeable skin. This unique feature allows frogs to "breathe" largely through their skin.^{[citation needed]} Because the oxygen is dissolved in an aqueous film on the skin and passes from there to the blood, the skin must remain moist at all times; this makes frogs susceptible to many toxins in the environment, some of which can similarly dissolve in the layer of water and be passed into their bloodstream. This may be the cause of the decline in frog populations.^{[5][6][7][8][9][10][11][12][13]}
Many characteristics are not shared by all of the approximately 5,250 described frog species. However, some general characteristics distinguish them from other amphibians. Frogs are usually well suited to jumping, with long hind legs and elongated ankle bones. They have a short vertebral column, with no more than ten free vertebrae, followed by a fused tailbone (urostyle or coccyx), typically resulting in a tailless phenotype.^{[citation needed]}
Frogs range in size from 10 mm (0.39 in) (Brachycephalus didactylus of Brazil and Eleutherodactylus iberia of Cuba) to 300 mm (12 in) (goliath frog, Conraua goliath, of Cameroon). The skin hangs loosely on the body because of the lack of loose connective tissue. Skin texture varies: it can be smooth, warty or folded. Frogs have three eyelid membranes: one is transparent to protect the eyes underwater, and two vary from translucent to opaque. Frogs have a tympanum on each side of the head, which is involved in hearing and, in some species, is covered by skin. Most frogs have teeth, specifically pedicellate teeth in which the crown is separated from the root by fibrous tissue. Most only have teeth on the edge of the upper jaw (maxillary teeth) as well as vomerine teeth on the roof of their mouth. They do not have any teeth on their lower jaw, so they usually swallow their food whole. The teeth are mainly used to hold the prey and keep it in place till they can get a good grip on it and swallow their meal, assisted by retracting their eyes into their head.^[14] True toads lack any teeth at all, and some species (Pyxicephalus) which prey on relatively large organisms (including mice and other frogs) have cone shaped projections of bone, called odontoid processes, at the front of the lower jaw which function like teeth.^[2]

Feet and legs

Tyler's Tree Frog (Litoria tyleri) illustrates large toe pads and webbed feet

A bullfrog skeleton, showing elongate limb bones and extra joints. Red marks indicate bones which have been substantially elongated in frogs and joints which have become mobile. Blue indicates joints and bones which have not been modified or only somewhat elongated.

The structure of the feet and legs varies greatly among frog species, depending in part on whether they live primarily on the ground, in water, in trees, or in burrows. Frogs must be able to move quickly through their environment to catch prey and escape predators, and numerous adaptations help them do so.
Many frogs, especially those that live in water, have webbed toes. The degree to which the toes are webbed is directly proportional to the amount of time the species lives in the water. For example, the completely aquatic African dwarf frog (Hymenochirus sp.) has fully webbed toes, whereas the toes of White's tree frog (Litoria caerulea), an arboreal species, are only a half or a quarter webbed.

A frog gripping on a palm frond.

Arboreal frogs have "toe pads" to help grip vertical surfaces. These pads, located on the ends of the toes, do not work by suction. Rather, the surface of the pad consists of interlocking cells, with a small gap between adjacent cells. When the frog applies pressure to the toe pads, the interlocking cells grip irregularities on the substrate. The small gaps between the cells drain away all but a thin layer of moisture on the pad, and maintain a grip through capillarity. This allows the frog to grip smooth surfaces, and does not function when the pads are excessively wet.^[15]
In many arboreal frogs, a small "intercalary structure" in each toe increases the surface area touching the substrate. Furthermore, since hopping through trees can be dangerous, many arboreal frogs have hip joints that allow both hopping and walking. Some frogs that live high in trees even possess an elaborate degree of webbing between their toes, as do aquatic frogs. In these arboreal frogs, the webs allow the frogs to "parachute" or control their glide from one position in the canopy to another.^[16]
Ground-dwelling frogs generally lack the adaptations of aquatic and arboreal frogs. Most have smaller toe pads, if any, and little webbing. Some burrowing frogs have a toe extension—a metatarsal tubercle—that helps them to burrow. The hind legs of ground dwellers are more muscular than those of aqueous and tree-dwelling frogs.
Sometimes during the tadpole stage, one of the animal's rear leg stubs is eaten by a dragonfly nymph. In some of these cases, the full leg grows anyway, and in other cases, it does not, although the frog may still live out its normal lifespan with only three legs. Other times, a parasitic flatworm called Riberoria trematodes digs into the rear of a tadpole, where it rearranges the limb bud cells, which sometimes causes the frog to have extra legs.^[17]

Jumping

Rainforest Rocket Frog jumping

Frogs are generally recognized as exceptional jumpers, and the best jumper of all vertebrates. The Australian rocket frog, Litoria nasuta, can leap over 50 times its body length (5.5 cm), resulting in jumps of over 2 meters. The acceleration of the jump may be up to twice gravity. There are tremendous differences between species in jumping capability, but within a species, jump distance increases with increasing size, but relative jumping distance (body-lengths jumped) decreases.
While frog species can use a variety of locomotor modes (running, walking, gliding, swimming, and climbing), more are either proficient at jumping or descended from ancestors who were, with much of the musculo-skeletal morphology modified for this purpose. The tibia, fibula and tarsals have been fused into a single, strong bone, as have the radius and ulna in the forelimbs (which must absorb the impact of landing). The metatarsals have become elongated to add to the leg length and allow the frog to push against the ground for longer during a jump. The illium has elongated and formed a mobile joint with the sacrum which, in specialist jumpers such as Ranids or Hylids, functions as an additional limb joint to further power the leaps. This elongation of the limbs results in the frog being able to apply force to the ground for longer during a jump, which in turn results in a longer, faster jump.^{[citation needed]}
The muscular system has been similarly modified. The hind limbs of the ancestor of frogs presumably contained pairs of muscles which would act in opposition (one muscle to flex the knee, a different muscle to extend it), as is seen in most other limbed animals. However, in modern frogs, almost all muscles have been modified to contribute to the action of jumping, with only a few small muscles remaining to bring the limb back to the starting position and maintain posture. The muscles have also been greatly enlarged, with the muscles involved in jumping accounting for over 17% of the total mass of the frog.
In some extremely capable jumpers, such as the cuban tree frog, the peak power exerted during a jump can exceed what muscle is capable of producing. Currently, it is hypothesized that frogs are storing muscular energy by stretching their tendons like springs, then triggering the release all at once, allowing the frog to increase the energy of its jump beyond the limits of muscle-powered acceleration. A similar mechanism has already been documented in locusts and grasshoppers.^[18]

Skin

Pouched Frog (Assa darlingtoni) camouflaged against leaf litter

Microscopic view of frog skin

Many frogs are able to absorb water and oxygen directly through the skin, especially around the pelvic area. However, the permeability of a frog's skin can also result in water loss. Some tree frogs reduce water loss with a waterproof layer of skin. Others have adapted behaviours to conserve water, including engaging in nocturnal activity and resting in a water-conserving position. This position involves the frog lying with its toes and fingers tucked under its body and chin, respectively, with no gap between the body and substrate. Some frog species will also rest in large groups, touching the skin of the neighbouring frog. This reduces the amount of skin exposed to the air or a dry surface, and thus reduces water loss. These adaptations only reduce water loss enough for a predominantly arboreal existence, and are not suitable for arid conditions.
Camouflage is a common defensive mechanism in frogs. Most camouflaged frogs are nocturnal, which adds to their ability to hide. Nocturnal frogs usually find the ideal camouflaged position during the day to sleep. Some frogs have the ability to change colour, but this is usually restricted to shades of one or two colours. For example, White's tree frog varies in shades of green and brown. Features such as warts and skin folds are usually found on ground-dwelling frogs, where a smooth skin would not disguise them effectively. Arboreal frogs usually have smooth skin, enabling them to disguise themselves as leaves.^{[citation needed]}
Certain frogs change colour between night and day, as light and moisture stimulate the pigment cells and cause them to expand or contract.

Poison

Many frogs contain mild toxins that make them unpalatable to potential predators. For example, all toads have large poison glands—the parotoid glands—located behind the eyes, on the top of the head. Some frogs, such as some poison dart frogs, are especially toxic. The chemical makeup of toxins in frogs varies from irritants to hallucinogens, convulsants, nerve poisons, and vasoconstrictors. Many predators of frogs have adapted to tolerate high levels of these poisons. Others, including humans, may be severely affected.

Oophaga pumilio, a poison dart frog, contains numerous alkaloids which deter predators

Some frogs obtain poisons from the ants and other arthropods they eat;^[19] others, such as the Australian Corroboree Frogs (Pseudophryne corroboree and Pseudophryne pengilleyi), can manufacture an alkaloid not derived from their diet.^[20] Some native people of South America extract poison from the poison dart frogs and apply it to their darts for hunting,^[21] although few species are toxic enough to be used for this purpose. It was previously a misconception the poison was placed on arrows rather than darts. The common name of these frogs was thus changed from "poison arrow frog" to "poison dart frog" in the early 1980s. Poisonous frogs tend to advertise their toxicity with bright colours, an adaptive strategy known as aposematism. There are at least two non-poisonous species of frogs in tropical America (Eleutherodactylus gaigei and Lithodytes lineatus) that mimic the colouration of dart poison frogs' coloration for self-protection (Batesian mimicry).^[22][23]
Because frog toxins are extraordinarily diverse, they have raised the interest of biochemists as a "natural pharmacy". The alkaloid epibatidine, a painkiller 200 times more potent than morphine, is found in some species of poison dart frogs. Other chemicals isolated from the skin of frogs may offer resistance to HIV infection.^[24] Arrow and dart poisons are under active investigation for their potential as therapeutic drugs.^[25]
The skin secretions of some toads, such as the Colorado River toad and cane toad, contain bufotoxins, some of which, such as bufotenin, are psychoactive, and have therefore been used as recreational drugs. Typically, the skin secretions are dried and smoked. Skin licking is especially dangerous, and appears to constitute an urban myth. See psychoactive toad.

Respiration and circulation

The skin of a frog is permeable to oxygen and carbon dioxide, as well as to water. There are a number of blood vessels near the surface of the skin. When a frog is underwater, oxygen is transmitted through the skin directly into the bloodstream. On land, adult frogs use their lungs to breathe. Their lungs are similar to those of humans, but the chest muscles are not involved in respiration, and there are no ribs or diaphragm to support breathing. Frogs breathe by taking air in through the nostrils (which often have valves which close when the frog is submerged), causing the throat to puff out, then compressing the floor of the mouth, which forces the air into the lungs. In August 2007 an aquatic frog named Barbourula kalimantanensis was discovered in a remote part of Indonesia. The Bornean Flat-headed Frog (B. kalimantanensis) is the first species of frog known to science without lungs.
Frogs are known for their three-chambered heart, which they share with all tetrapods except birds, crocodilians and mammals. In the three-chambered heart, oxygenated blood from the lungs and de-oxygenated blood from the respiring tissues enter by separate atria, and are directed via a spiral valve to the appropriate vessel—aorta for oxygenated blood and pulmonary artery for deoxygenated blood. This special structure is essential to keeping the mixing of the two types of blood to a minimum, which enables frogs to have higher metabolic rates, and to be more active than otherwise.
Some species of frog have remarkable adaptations that allow them to survive in oxygen deficient water. The lake titicaca frog (Telmatobius culeus) is one such species and to survive in the poorly oxygenated waters of Lake Titicaca it has incredibly wrinkly skin that increases its surface area to enhance gas exchange. This frog will also do 'push-ups' on the lake bed to increase the flow of water around its body.^[26]

Digestion and excretion

The frog's digestive system begins with the mouth. Frogs have teeth along their upper jaw called the maxillary teeth, which are used to grind food before swallowing. These teeth are very weak, and cannot be used to catch or harm agile prey. Instead, the frog uses its sticky tongue to catch food (such as flies or other insects). The food then moves through the esophagus into the stomach. The food then proceeds to the small intestine (duodenum and ileum) where most digestion occurs. Frogs carry pancreatic juice from the pancreas, and bile (produced by the liver) through the gallbladder from the liver to the small intestine, where the fluids digest the food and extract the nutrients. When the food passes into the large intestine, the water is reabsorbed and wastes are routed to the cloaca. All wastes exit the body through the cloaca and the cloacal vent.

Nervous system

The frog has a highly developed nervous system which consists of a brain, spinal cord and nerves. Many parts of the frog's brain correspond with those of humans. The medulla oblongata regulates respiration, digestion, and other automatic functions. Muscular coordination and posture are controlled by the cerebellum. The relative size of the cerebrum of a frog is much smaller than that of a human. Frogs have ten cranial nerves (nerves which pass information from the outside directly to the brain) and ten pairs of spinal nerves (nerves which pass information from extremities to the brain through the spinal cord). By contrast, all amniotes (mammals, birds and reptiles) have twelve cranial nerves. Frogs do not have external ears; the eardrums (tympanic membranes) are directly exposed. As in all animals, the ear contains semicircular canals which help control balance and orientation. Due to their short cochlea, frogs use electrical tuning to expand their range of audible frequencies.

Natural history

The life cycle of frogs, like that of other amphibians, consists of four main stages: egg, tadpole, metamorphosis and adult. The reliance of frogs on an aquatic environment for the egg and tadpole stages gives rise to a variety of breeding behaviours that include the well-known mating calls used by the males of most species to attract females to the bodies of water that they have chosen for breeding. Some frogs also look after their eggs—and in some cases even the tadpoles—for some time after laying.

Life cycle

Frogspawn

Frogspawn development

Tadpole of Haswell's Froglet (Paracrinia haswelli

The life cycle of a frog starts with an egg. A female generally lays gelatinous egg masses containing thousands of eggs, in water. Each anuran species lays eggs in a distinctive, identifiable manner. An example are the long strings of eggs laid by the common American toad. The eggs are highly vulnerable to predation, so frogs have evolved many techniques to ensure the survival of the next generation. In colder areas the embryo is black to absorb more heat from the sun, which speeds up the development. Most commonly, this involves synchronous reproduction. Many individuals will breed at the same time, overwhelming the actions of predators; the majority of the offspring will still die due to predation, but there is a greater chance some will survive. Another way in which some species avoid the predators and pathogens eggs are exposed to in ponds is to lay eggs on leaves above the pond, with a gelatinous coating designed to retain moisture. In these species the tadpoles drop into the water upon hatching. The eggs of some species laid out of water can detect vibrations of nearby predatory wasps or snakes, and will hatch early to avoid being eaten.^[27] Some species, such as the Cane Toad (Bufo marinus), lay poisonous eggs to minimise predation. While the length of the egg stage depends on the species and environmental conditions, aquatic eggs generally hatch within one week. Other species go through their whole larval phase inside the eggs or the mother, or they have direct development. Unlike salamanders and newts, frogs and toads never become sexually mature while still in their larval stage.
Eggs hatch and continue life as tadpoles (occasionally known as polliwogs), which typically have oval bodies and long, vertically flattened tails. At least one species (Nannophrys ceylonensis) has tadpoles that are semi-terrestrial and live among wet rocks,^[28][29] but as a general rule, free living larvae are fully aquatic. They lack eyelids and have a cartilaginous skeleton, a lateral line system, gills for respiration (external gills at first, internal gills later) and tails with dorsal and ventral folds of skin for swimming.^[30] From pretty early onward they develop a gill pouch that covers the gills and the front legs and also the lungs are developed in an early stage as an accessory breathing organ. Some species which go through the metamorphosis inside the egg and hatch to small frogs never develop gills, instead there are specialised areas of skin that takes care of the respiration. Tadpoles also lack true teeth, but the jaws in most species usually have two elongate, parallel rows of small keratinized structures called keradonts in the upper jaw while the lower jaw has three rows of keradonts, surrounded by a horny beak, but the number of rows can be lower or absent, or much higher.^[31] Tadpoles are typically herbivorous, feeding mostly on algae, including diatoms filtered from the water through the gills. Some species are carnivorous at the tadpole stage, eating insects, smaller tadpoles, and fish. Cannibalism has been observed among tadpoles. Early developers who gain legs may be eaten by the others, so the late bloomers survive longer. This has been observed in England in the species Rana temporaria (common frog).^[32]
Tadpoles are highly vulnerable to predation by fish, newts, predatory diving beetles and birds such as kingfishers. Poisonous tadpoles are present in many species, such as Cane Toads. The tadpole stage may be as short as a week, or tadpoles may overwinter and metamorphose the following year in some species, such as the midwife toad (Alytes obstetricans) and the common spadefoot (Pelobates fuscus). In the Pipidae, with the exception for Hymenochirus, the tadpoles have paired anterior barbels which make them resemble small catfish.^[33]
With the exception of the base of the tail, where a few vertebral structures develop to give rise to the urostyle later in life, the tail lacks the completely solid, segmental, skeletal elements of cartilage or bony tissue that are so typical for other vertebrates, although it does contain a notochord
At the end of the tadpole stage, frogs undergo metamorphosis, in which they undergo a transition into the adult form. This metamorphosis last typically only 24 hours and consists of:

Larva of the common frog Rana temporaria a day before metamorphisis

Common frog - Metamorphosis stage. Notice the deformed jaws, large eyes and the remains of the gill pouch.

Young frog with tail remains after metamorphosis

Adult leopard frog

• The disappearance of the gill pouch, making the front legs visible.
• The transformation of the jaws into the big jaws of predatory frogs (most tadpoles are scrapers of algae or are filter feeders)
• The transformation of the digestive system: the long spiral gut of the larva is being replaced by the typical short gut of a predator.
• An adaptation of the nervous system for stereoscopic vision, locomotion and feeding
• A quick growth and movement of the eyes to higher up the skull and the formation of eyelids.
• Formation of skin glands, thickening of the skin and loss of the lateral line system
• An eardrum is developed to lock the middle ear.

The disappearance of the tail is somewhat later (occurs at higher thyroxin levels) and after the tail has been resorbed the animals are ready to leave the water. The material of the tail is being used for a quick growth of the legs. The disappearing of the larval structures is a regulated process called apoptosis.

Incident of frog cannibalism

After metamorphosis, young adults may leave the water and disperse into terrestrial habitats, or continue to live in the aquatic habitat as adults. Almost all species of frogs are carnivorous as adults, eating invertebrates such as arthropods, annelids and gastropods. A few of the larger species may eat prey such as small mammals, fish and smaller frogs. Some frogs use their sticky tongues to catch fast-moving prey, while others capture their prey and force it into their mouths with their hands. However, there are a very few species of frogs that primarily eat plants.^[34] Adult frogs are themselves preyed upon by birds, large fish, snakes, otters, foxes, badgers, coatis, and other animals. Frogs are also eaten by people (see section on uses in agriculture and research, below).
Frogs and toads can live for many years; though little is known about their life span in the wild, captive frogs and toads are recorded living up to 40 years.^[35]
Frogs from temperate climates hibernate through the winter, and 4 species are known to freeze during this time, most notably Rana sylvatica.^[36]

Reproduction of frogs

Once adult frogs reach maturity, they will assemble at a water source such as a pond or stream to breed. Many frogs return to the bodies of water where they were born, often resulting in annual migrations involving thousands of frogs. In continental Europe, a large proportion of migrating frogs used to die on roads, before special fences and tunnels were built for them.

Male and female Common toad (Bufo bufo) in amplexus

A Male and Female common toad in amplexus. The black strands are eggs released into open water minutes after birth.

Once at the breeding ground, male frogs call to attract a mate, collectively becoming a chorus of frogs. The call is unique to the species, and will attract females of that species. Some species have satellite males who do not call, but intercept females that are approaching a calling male.
The male and female frogs then undergo amplexus. This involves the male mounting the female and gripping her (sometimes with special nuptial pads) tightly. Fertilization is external: the egg and sperm meet outside of the body. The female releases her eggs, which the male frog covers with a sperm solution. The eggs then swell and develop a protective coating. The eggs are typically brown or black, with a clear, gelatin-like covering.
Most temperate species of frogs reproduce between late autumn and early spring. In the UK, most common frog populations produce frogspawn in February, although there is wide variation in timing. Water temperatures at this time of year are relatively low, typically between four and 10 degrees Celsius. Reproducing in these conditions helps the developing tadpoles because dissolved oxygen concentrations in the water are highest at cold temperatures. More importantly, reproducing early in the season ensures that appropriate food is available to the developing frogs at the right time.

Parental care

Colour plate from Ernst Haeckel's 1904 Kunstformen der Natur, depicting frog species that include two examples of parental care.

Although care of offspring is poorly understood in frogs, it is estimated that up to 20% of amphibian species may care for their young in one way or another, and there is a great diversity of parental behaviours.^[37] Some species of poison dart frog lay eggs on the forest floor and protect them, guarding the eggs from predation and keeping them moist. The frog will urinate on them if they become too dry. After hatching, a parent (the sex depends upon the species) will move them, on its back, to a water-holding bromeliad. The parent then feeds them by laying unfertilized eggs in the bromeliad until the young have metamorphosed. Other frogs carry the eggs and tadpoles on their hind legs or back (e.g. the midwife toads, Alytes spp.). Some frogs even protect their offspring inside their own bodies. The male Australian Pouched Frog (Assa darlingtoni) has pouches along its side in which the tadpoles reside until metamorphosis. The female Gastric-brooding Frogs (genus Rheobatrachus) from Australia, now probably extinct, swallows its tadpoles, which then develop in the stomach. To do this, the Gastric-brooding Frog must stop secreting stomach acid and suppress peristalsis (contractions of the stomach). Darwin's Frog (Rhinoderma darwinii) from Chile puts the tadpoles in its vocal sac (see next section) for development. Some species of frog will leave a 'babysitter' to watch over the frogspawn until it hatches.
The evolution of parental care in frogs is driven primarily by the size of the water body in which they breed. There is an inverse relationship between the level of parental care in a frog species and the size of the body of water—frogs that breed in smaller water bodies tend to have more complex parental care behaviors.^[38] Water body size shows this strong relationship with parental care because it encompasses several important variables that interact to select for parental care: predation, desiccation, competition, and resource limitation. Because predation of eggs and larvae is high in large water bodies, a number of frog species evolved terrestrial oviposition. Once eggs are deposited on land, the desiccating terrestrial environment demands uniparental care in the form of egg hydration to ensure egg survival.^[39] The subsequent need to transport hatched tadpoles to a water source requires an even more intense form of uniparental care. In small water bodies where predators are mostly absent, such as phytotelmata (water-filled leaf axils or small woody cavities), inter-tadpole competition becomes the variable that constrains tadpole survival. Certain frogs species avoid this competition by evolving the use of smaller phytotelmata as tadpole deposition sites.^[40] However, while these smaller tadpole rearing sites are free of competition, they also lack nutrients. Because they do not have sufficient nutrients to support a tadpole without parental provisioning behavior, frog species that transitioned from the use of larger to smaller phytotelmata have evolved trophic (unfertilized) egg laying. In this complex form of biparental care, the female provides her offspring with nutritive eggs. While each of these variables select for different behaviors, they correlate with the size of a species' tadpole-rearing site and influence the degree of parental care displayed by a species.

Call

A male Dendropsophus microcephalus displaying its vocal sac during its call.

Some frog calls are so loud, they can be heard up to a mile away.^[41] The call of a frog is unique to its species. Frogs call by passing air through the larynx in the throat. In most calling frogs, the sound is amplified by one or more vocal sacs, membranes of skin under the throat or on the corner of the mouth that distend during the amplification of the call. The field of neuroethology studies the neurocircuitry that underlies frog audition.
Some frogs lack vocal sacs, such as those from the genera Heleioporus and Neobatrachus, but these species can still produce a loud call. Their buccal cavity is enlarged and dome-shaped, acting as a resonance chamber that amplifies their call. Species of frog without vocal sacs and that do not have a loud call tend to inhabit areas close to flowing water. The noise of flowing water overpowers any call, so they must communicate by other means.
The main reason for calling is to allow males to attract a mate. Males call either individually or in a group called a chorus. Females of many frog species, for example Polypedates leucomystax, produce calls reciprocal to the males', which act as the catalyst for the enhancement of reproductive activity in a breeding colony.^[42] A male frog emits a release call when mounted by another male. Tropical species also have a rain call that they make on the basis of humidity cues prior to a rain shower. Many species also have a territorial call that is used to chase away other males. All of these calls are emitted with the mouth of the frog closed.
A distress call, emitted by some frogs when they are in danger, is produced with the mouth open, resulting in a higher-pitched call. The effectiveness of the call is unknown; however, it is suspected the call intrigues the predator until another animal is attracted, distracting them enough for its escape.
Many species of frog have deep calls, or croaks. The English onomatopoeic spelling is "ribbit". The croak of the American bullfrog (Rana catesbiana) is sometimes spelt "jug o' rum".^[43] Other examples are Ancient Greek brekekekex koax koax for probably Rana ridibunda, and the description in Rigveda 7:103.6 gómāyur éko ajámāyur ékaħ = "one has a voice like a cow's, one has a voice like a goat's".

Distribution and conservation status

The Red-eyed Tree Frog (Litoria chloris) is a species of tree frog native to eastern Australia.

See also: Decline in amphibian populations

The habitat of frogs extends almost worldwide, but they do not occur in Antarctica and are not present on many oceanic islands.^[44][45] The greatest diversity of frogs occurs in the tropical areas of the world, where water is readily available, suiting frogs' requirements due to their skin. Some frogs inhabit arid areas such as deserts, where water may not easily accesible,and rely on specific adaption to survive.

Platypus

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For other uses, see Platypus (disambiguation).

Platypus[1] Temporal range: 66–0 Ma PreЄ Є O S D C P T J K Pg N Late Cretaceous to Recent
Conservation status
Least Concern (IUCN 3.1)[2]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Monotremata
Family:	Ornithorhynchidae
Genus:	Ornithorhynchus Blumenbach, 1800
Species:	O. anatinus
Binomial name
Ornithorhynchus anatinus (Shaw, 1799)
Platypus range (blue — native, red — introduced)

The platypus (Ornithorhynchus anatinus) is a semi-aquatic mammal endemic to eastern Australia, including Tasmania. Together with the four species of echidna, it is one of the five extant species of monotremes, the only mammals that lay eggs instead of giving birth to live young. It is the sole living representative of its family (Ornithorhynchidae) and genus (Ornithorhynchus), though a number of related species have been found in the fossil record.
The bizarre appearance of this egg-laying, venomous, duck-billed, beaver-tailed, otter-footed mammal baffled European naturalists when they first encountered it, with some considering it an elaborate fraud. It is one of the few venomous mammals, the male platypus having a spur on the hind foot that delivers a venom capable of causing severe pain to humans. The unique features of the platypus make it an important subject in the study of evolutionary biology and a recognisable and iconic symbol of Australia; it has appeared as a mascot at national events and is featured on the reverse of the Australian 20 cent coin. The platypus is the animal emblem of the state of New South Wales.^[3]
Until the early 20th century it was hunted for its fur, but it is now protected throughout its range. Although captive breeding programmes have had only limited success and the platypus is vulnerable to the effects of pollution, it is not under any immediate threat.

Contents [hide] 1 Taxonomy and etymology 2 Description 2.1 Venom 2.2 Electrolocation 3 Ecology and behaviour 3.1 Reproduction 3.2 Sleep 4 Evolution 5 Conservation status 6 Platypus in wildlife sanctuaries 6.1 Queensland 6.1.1 Gold Coast 6.1.2 Brisbane 6.2 New South Wales 6.2.1 Sydney 6.3 Victoria 6.3.1 Healesville 6.4 South Australia 6.4.1 Mylor 7 Cultural references 8 See also 9 Notes 10 References 11 External links

Taxonomy and etymology

When the platypus was first encountered by Europeans in 1798, a pelt and sketch were sent back to Great Britain by Captain John Hunter, the second Governor of New South Wales.^[4] British scientists' initial hunch was that the attributes were a hoax.^[5] George Shaw, who produced the first description of the animal in the Naturalist's Miscellany in 1799, stated that it was impossible not to entertain doubts as to its genuine nature, and Robert Knox believed it might have been produced by some Asian taxidermist.^[5] It was thought that somebody had sewn a duck's beak onto the body of a beaver-like animal. Shaw even took a pair of scissors to the dried skin to check for stitches.^[6]
The common name "platypus" is the latinisation of the Greek word πλατύπους (platupous), "flat-footed",^[7] from πλατύς (platus), "broad, wide, flat"^[8] and πούς (pous), "foot".^[9][10] Shaw assigned it as a Linnaean genus name when he initially described it, but the term was quickly discovered to belong already to the wood-boring ambrosia beetle (genus Platypus).^[11] It was independently described as Ornithorhynchus paradoxus by Johann Blumenbach in 1800 (from a specimen given to him by Sir Joseph Banks)^[12] and following the rules of priority of nomenclature it was later officially recognised as Ornithorhynchus anatinus.^[11] The scientific name Ornithorhynchus anatinus is derived from ορνιθόρυνχος ("ornithorhynkhos"), which literally means "bird snout" in Greek, and anatinus, which means "duck-like" in Latin.
There is no universally agreed plural of "platypus" in the English language. Scientists generally use "platypuses" or simply "platypus". Colloquially the term "platypi" is also used for the plural, although this is technically incorrect and a form of pseudo-Latin;^[6] the correct Greek plural would be "platypodes". Early British settlers called it by many names, such as watermole, duckbill, and duckmole.^[6] The name "platypus" is often prefixed with the adjective "duck-billed" to form duck-billed platypus, despite there being only one species of platypus.^[13]

Description

The body and the broad, flat tail of the platypus are covered with dense brown fur that traps a layer of insulating air to keep the animal warm.^[6][11] The fur is waterproof, and the texture is akin to that of a mole.^[14] The platypus uses its tail for storage of fat reserves (an adaptation also found in animals such as the Tasmanian Devil^[15] and fat-tailed sheep). It has webbed feet and a large, rubbery snout; these are features that appear closer to those of a duck than to those of any known mammal. The webbing is more significant on the front feet and is folded back when walking on land.^[11] Unlike a bird's beak (in which the upper and lower parts separate to reveal the mouth), the snout of the platypus is a sensory organ with the mouth on the underside. The nostrils are located on the dorsal surface of the snout, while the eyes and ears are located in a groove set just back from it; this groove is closed when swimming.^[11] Platypuses have been heard to emit a low growl when disturbed and a range of other vocalisations have been reported in captive specimens.^[6]

A colour print of platypuses from 1863

Weight varies considerably from 0.7 to 2.4 kg (1.5 to 5.3 lb), with males being larger than females: males average 50 cm (20 in) in total length while females average 43 cm (17 in).^[11] There is substantial variation in average size from one region to another, and this pattern does not seem to follow any particular climatic rule and may be due to other environmental factors such as predation and human encroachment.^[16]
The platypus has an average body temperature of about 32 °C (90 °F) rather than the 37 °C (99 °F) typical of placental mammals.^[17] Research suggests this has been a gradual adaptation to harsh environmental conditions on the part of the small number of surviving monotreme species rather than a historical characteristic of monotremes.^[18][19]
Modern platypus young have three-cusped molars, which they lose before or just after leaving the breeding burrow;^[20][21] adults have heavily keratinised pads in their place.^[11] The platypus jaw is constructed differently from that of other mammals, and the jaw-opening muscle is different.^[11] As in all true mammals, the tiny bones that conduct sound in the middle ear are fully incorporated into the skull, rather than lying in the jaw as in cynodonts and other pre-mammalian synapsids. However, the external opening of the ear still lies at the base of the jaw.^[11] The platypus has extra bones in the shoulder girdle, including an interclavicle, which is not found in other mammals.^[11] It has a reptilian gait, with legs that are on the sides of the body, rather than underneath.^[11] When on land it engages in knuckle-walking to protect the webbing between its toes.^[22]

Venom

Main article: Platypus venom

The calcaneus spur found on the male's hind limb is used to deliver venom.

While both male and female platypuses are born with ankle spurs, only the male has spurs which produce a cocktail of venom,^[23][24][25] composed largely of defensin-like proteins (DLPs), three of which are unique to the platypus.^[26] The defensin proteins are produced by the immune system of the platypus. Although powerful enough to kill smaller animals such as dogs, the venom is not lethal to humans, but is so excruciating that the victim may be incapacitated.^[26][27] Oedema rapidly develops around the wound and gradually spreads throughout the affected limb. Information obtained from case histories and anecdotal evidence indicates that the pain develops into a long-lasting hyperalgesia (a heightened sensitivity to pain) that persists for days or even months.^[28][29] Venom is produced in the crural glands of the male, which are kidney-shaped alveolar glands connected by a thin-walled duct to a calcaneus spur on each hind limb. The female platypus, in common with echidnas, has rudimentary spur buds which do not develop (dropping off before the end of their first year) and lack functional crural glands.^[11]
The venom appears to have a different function from those produced by non-mammalian species: its effects are not life-threatening to humans but nevertheless powerful enough to seriously impair the victim. Since only males produce venom and production rises during the breeding season, it is theorised that it is used as an offensive weapon to assert dominance during this period.^[26]

Electrolocation

Platypus (Ornithorhynchus anatinus)

Monotremes (for the other species, see Echidna) are the only mammals known to have a sense of electroreception: they locate their prey in part by detecting electric fields generated by muscular contractions. The platypus' electroreception is the most sensitive of any monotreme.^[30][31]
The electroreceptors are located in rostro-caudal rows in the skin of the bill, while mechanoreceptors (which detect touch) are uniformly distributed across the bill. The electrosensory area of the cerebral cortex is contained within the tactile somatosensory area, and some cortical cells receive input from both electroreceptors and mechanoreceptors, suggesting a close association between the tactile and electric senses. Both electroreceptors and mechanoreceptors in the bill dominate the somatotopic map of the platypus brain, in the same way human hands dominate the Penfield homunculus map.^[32][33]
The platypus can determine the direction of an electric source, perhaps by comparing differences in signal strength across the sheet of electroreceptors. This would explain the characteristic side-to-side motion of the animal's head while hunting. The cortical convergence of electrosensory and tactile inputs suggests a mechanism for determining the distance of prey items which, when they move, emit both electrical signals and mechanical pressure pulses: the difference between the times of arrival of the two signals would allow computation of distance.^[31]
The platypus feeds by neither sight nor smell,^[34] closing its eyes, ears, and nose each time it dives.^[35] Rather, when it digs in the bottom of streams with its bill, its electroreceptors detect tiny electrical currents generated by muscular contractions of its prey, so enabling it to distinguish between animate and inanimate objects, which continuously stimulate its mechanoreceptors.^[31] Experiments have shown that the platypus will even react to an "artificial shrimp" if a small electrical current is passed through it.^[36]

Ecology and behaviour

Dentition, as illustrated in Knight's Sketches in Natural History

The platypus is very difficult to spot even on the surface of a river.

Platypus swimming

Swimming underwater at Sydney Aquarium, Australia

The platypus is semi-aquatic, inhabiting small streams and rivers over an extensive range from the cold highlands of Tasmania and the Australian Alps to the tropical rainforests of coastal Queensland as far north as the base of the Cape York Peninsula.^[37] Inland, its distribution is not well known: it is extinct in South Australia (apart from an introduced population on Kangaroo Island)^[38] and is no longer found in the main part of the Murray–Darling Basin, possibly due to the declining water quality brought about by extensive land clearing and irrigation schemes.^[39] Along the coastal river systems, its distribution is unpredictable; it appears to be absent from some relatively healthy rivers, and yet maintains a presence in others that are quite degraded (the lower Maribyrnong, for example).^[40]
In captivity platypuses have survived to seventeen years of age, and wild specimens have been recaptured when eleven years old. Mortality rates for adults in the wild appear to be low.^[11] Natural predators include snakes, water rats, goannas, hawks, owls, and eagles. Low platypus numbers in northern Australia are possibly due to predation by crocodiles.^[41] The introduction of red foxes in 1845 for hunting may have had some impact on its numbers on the mainland.^[16] The platypus is generally regarded as nocturnal and crepuscular, but individuals are also active during the day, particularly when the sky is overcast.^[42][43] Its habitat bridges rivers and the riparian zone for both a food supply of prey species and banks where it can dig resting and nesting burrows.^[43] It may have a range of up to 7 km (4.3 mi), with a male's home range overlapping those of 3 or 4 females.^[44]
The platypus is an excellent swimmer and spends much of its time in the water foraging for food. When swimming it can be distinguished from other Australian mammals by the absence of visible ears.^[45] Uniquely among mammals it propels itself when swimming by an alternate rowing motion of the front two feet; although all four feet of the platypus are webbed, the hind feet (which are held against the body) do not assist in propulsion, but are used for steering in combination with the tail.^[46] The species is endothermic, maintaining its body temperature at about 32 °C (90 °F), lower than most mammals, even while foraging for hours in water below 5 °C (41 °F).^[11]
Dives normally last around 30 seconds but can last longer, although few exceed the estimated aerobic limit of 40 seconds. Recovery at the surface between dives commonly takes from 10 to 20 seconds.^[47][48] The platypus is a carnivore: it feeds on annelid worms and insect larvae, freshwater shrimps, and yabbies (freshwater crayfish) that it digs out of the riverbed with its snout or catches while swimming. It utilises cheek-pouches to carry prey to the surface, where they are eaten.^[45] The platypus needs to eat about 20% of its own weight each day. This requires the platypus to spend an average of 12 hours each day looking for food.^[47] When not in the water, the platypus retires to a short, straight resting burrow of oval cross-section, nearly always in the riverbank not far above water level, and often hidden under a protective tangle of roots.^[45]

Reproduction

When the platypus was first encountered by European naturalists, they were divided over whether the female laid eggs. This was not confirmed until 1884 when W. H. Caldwell was sent to Australia where, after extensive searching assisted by a team of 150 Aborigines, he managed to discover a few eggs.^[11][26] Mindful of the high cost per word of wiring England, Caldwell famously but tersely wired London, "Monotremes oviparous, ovum meroblastic." That is, monotremes lay eggs, and the eggs are similar to those of reptiles in that only part of the egg divides as it develops.
The species exhibits a single breeding season; mating occurs between June and October, with some local variation taking place between different populations across its range.^[41] Historical observation, mark-and-recapture studies, and preliminary investigations of population genetics indicate the possibility of both resident and transient members of populations and suggest a polygynous mating system.^[49] Females are thought likely to become sexually mature in their second year, with breeding confirmed still to take place in animals over nine years old.^[49]
Outside the mating season, the platypus lives in a simple ground burrow whose entrance is about 30 cm (12 in) above the water level. After mating, the female constructs a deeper, more elaborate burrow up to 20 m (66 ft) long and blocked at intervals with plugs (which may act as a safeguard against rising waters or predators, or as a method of regulating humidity and temperature).^[50] The male takes no part in caring for its young, and retreats to its year-long burrow. The female softens the ground in the burrow with dead, folded, wet leaves and she fills the nest at the end of the tunnel with fallen leaves and reeds for bedding material. This material is dragged to the nest by tucking it underneath her curled tail.^[6]
The female platypus has a pair of ovaries but only the left one is functional.^[42] It lays one to three (usually two) small, leathery eggs (similar to those of reptiles), that are about 11 mm (0.43 in) in diameter and slightly rounder than bird eggs.^[51] The eggs develop in utero for about 28 days with only about 10 days of external incubation (in contrast to a chicken egg, which spends about 1 day in tract and 21 days externally).^[42] After laying her eggs, the female curls around them. The incubation period is divided into three phases. In the first phase, the embryo has no functional organs and relies on the yolk sac for sustenance. The yolk is absorbed by the developing young.^[52] During the second phase, the digits develop and, in the last phase, the egg tooth appears.^[53]
The newly hatched young are vulnerable, blind, and hairless, and are fed by the mother's milk. Although possessing mammary glands, the platypus lacks teats. Instead, milk is released through pores in the skin. There are grooves on her abdomen in which the milk pools, allowing the young to lap it up.^[6][41] After they hatch, the offspring are suckled for three to four months. During incubation and weaning, the mother initially leaves the burrow only for short periods, to forage. When doing so, she creates a number of thin soil plugs along the length of the burrow, possibly to protect the young from predators; pushing past these on her return forces water from her fur and allows the burrow to remain dry.^[54] After about five weeks, the mother begins to spend more time away from her young and, at around four months, the young emerge from the burrow.^[41] A platypus is born with teeth, but these drop out at a very early age, leaving the horny plates with which it grinds its food.^[55]

Sleep

Further information: Sleep (non-human)

The average sleep time of a platypus is said to be as long as 14 hours day. This is thought to possibly be because they eat crustaceans which provide a high level of calories.^[56]

Evolution

Platypus skeleton

The platypus and other monotremes were very poorly understood and some of the 19th century myths that grew up around them—for example, that the monotremes were "inferior" or quasi-reptilian—still endure.^[57] In 1947, William King Gregory theorised that placental mammals and marsupials may have diverged earlier and a subsequent branching divided the monotremes and marsupials, but later research and fossil discoveries have suggested this is incorrect.^[57][58] In fact, modern monotremes are the survivors of an early branching of the mammal tree, and a later branching is thought to have led to the marsupial and placental groups.^[57][59] Molecular clock and fossil dating suggest platypuses split from echidnas around 19–48 million years ago.^[60]

Platypus Echidnas  live birth  Marsupials  true placenta  Eutherians

Evolutionary relationships between the platypus and other mammals.[61]

The oldest discovered fossil of the modern platypus dates back to about 100,000 years ago, during the Quaternary period. The extinct monotremes Teinolophos and Steropodon were closely related to the modern platypus.^[58] The fossilised Steropodon was discovered in New South Wales and is composed of an opalised lower jawbone with three molar teeth (whereas the adult contemporary platypus is toothless). The molar teeth were initially thought to be tribosphenic, which would have supported a variation of Gregory's theory, but later research has suggested that, while they have three cusps, they evolved under a separate process.^[20] The fossil is thought to be about 110 million years old, which means that the platypus-like animal was alive during the Cretaceous period, making it the oldest mammal fossil found in Australia. Monotrematum sudamericanum, another fossil relative of the platypus, has been found in Argentina, indicating that monotremes were present in the supercontinent of Gondwana when the continents of South America and Australia were joined via Antarctica (up to about 167 million years ago).^[20][62]
Because of the early divergence from the therian mammals and the low numbers of extant monotreme species, the platypus is a frequent subject of research in evolutionary biology. In 2004, researchers at the Australian National University discovered the platypus has ten sex chromosomes, compared with two (XY) in most other mammals (for instance, a male platypus is always XYXYXYXYXY),^[63] although, given the XY designation of mammals, the sex chromosomes of the platypus are more similar to the ZZ/ZW sex chromosomes found in birds.^[64] The platypus genome also has both reptilian and mammalian genes associated with egg fertilisation.^[65] Since the platypus lacks the mammalian sex-determining gene SRY, the mechanism of sex determination remains unknown.^[66] A draft version of the platypus genome sequence was published in Nature on 8 May 2008, revealing both reptilian and mammalian elements, as well as two genes found previously only in birds, amphibians, and fish. More than 80% of the platypus' genes are common to the other mammals whose genomes have been sequenced.^[65]

Conservation status

A depiction of a platypus from a book for children published in Germany in 1798

Except for its loss from the state of South Australia, the platypus occupies the same general distribution as it did prior to European settlement of Australia. However, local changes and fragmentation of distribution due to human modification of its habitat are documented. Its current and historical abundance, however, are less well-known and it has probably declined in numbers, although still being considered as common over most of its current range.^[43] The species was extensively hunted for its fur until the early years of the 20th century and, although protected throughout Australia since 1905,^[54] until about 1950 it was still at risk of drowning in the nets of inland fisheries.^[39] The platypus does not appear to be in immediate danger of extinction thanks to conservation measures, but it could be impacted by habitat disruption caused by dams, irrigation, pollution, netting, and trapping.^[2] The IUCN lists the platypus on its Red List as Least Concern.^[2]
Platypuses generally suffer from few diseases in the wild; however, there is widespread public concern in Tasmania about the potential impacts of a disease caused by the fungus Mucor amphibiorum. The disease (termed Mucormycosis) affects only Tasmanian platypuses and has not been observed in platypuses in mainland Australia. Affected platypuses can develop ugly skin lesions or ulcers on various parts of the body, including their backs, tails, and legs. Mucormycosis can kill platypuses, death arising from secondary infection and by affecting the animals' ability to maintain body temperature and forage efficiency. The Biodiversity Conservation Branch at the Department of Primary Industries and Water are collaborating with NRM north and University of Tasmania researchers to determine the impacts of the disease on Tasmanian platypuses, as well as the mechanism of transmission and current spread of the disease.^[67] Until recently, the introduced red fox (Vulpes vulpes) was confined to mainland Australia, but growing evidence now indicates that it is present in low numbers in Tasmania.^[68]
Much of the world was introduced to the platypus in 1939 when National Geographic Magazine published an article on the platypus and the efforts to study and raise it in captivity. The latter is a difficult task, and only a few young have been successfully raised since—notably at Healesville Sanctuary in Victoria. The leading figure in these efforts was David Fleay, who established a platypusary—a simulated stream in a tank—at the Healesville Sanctuary, where breeding was successful in 1943. In 1972, he found a dead baby of about 50 days old, which had presumably been born in captivity, at his wildlife park at Burleigh Heads on the Gold Coast, Queensland.^[69] Healesville repeated its success in 1998 and again in 2000 with a similar stream tank. Taronga Zoo in Sydney bred twins in 2003, and breeding was again successful there in 2006.^[70]

Platypus in wildlife sanctuaries

Platypus House at Lone Pine Koala Sanctuary in Brisbane, Queensland

The platypus can be seen in special aquariums at the following Australian wildlife sanctuaries:

Queensland

Gold Coast

• David Fleay Wildlife Park

Brisbane

• Lone Pine Koala Sanctuary ^[71]
• Walkabout Creek Wildlife Centre

New South Wales

Sydney

• Taronga Zoo

Victoria

Healesville

• Healesville Sanctuary, near Melbourne, where the first platypus was bred in captivity, during 1943, by naturalist David Fleay.

South Australia

Mylor

• Warrawong Sanctuary near Mylor in the Adelaide Hills (near Adelaide).

Cultural references

The Australian 20 cent coin features a platypus

Since the introduction of decimal currency to Australia in 1966, the embossed image of a platypus has appeared on the reverse (tail) side of the 20 cent coin.
The platypus has been used several times as a mascot: "Syd" the platypus was one of the three mascots chosen for the Sydney 2000 Olympics along with an echidna and a kookaburra,^[72] "Expo Oz" the platypus was the mascot for World Expo 88, which was held in Brisbane in 1988,^[73] and Hexley the platypus is the mascot for Apple Computer's BSD-based Darwin operating system, Mac OS X.^[74] The platypus is also the mascot for the currently inactive Wenatchee Valley Venom arena football team located in Wenatchee, Washington.
The Platypus Trophy was made as an award for the winner of the college rivalry between the Oregon Ducks and the Oregon State Beavers.
The platypus has also been featured in songs, such as Green Day's "Platypus (I Hate You)" and Mr. Bungle's "Platypus". It is the subject of a children's poem by Banjo Paterson,^[75] and it also frequently appears as a character in children's television programmes, for example, the Platypus Family on Mister Rogers' Neighborhood, Perry the Platypus on the show Phineas and Ferb, and Ovide, the star of the cartoon Ovide and the Gang.^[76]
In the 1980s, the platypus was the main animal featured on promotional ads for the educational animal encyclopedia "Wildlife Treasury". In the ad, an excited young boy exclaims: "The Duck Billed Platypus has feet like a duck but it's furry! It's all in my Wildlife Treasury!"
The platypus is sometimes jokingly referred to as proof that God has a sense of humour (at the beginning of the film Dogma, for example; Robin Williams implied that He was also stoned on marijuana at the time^[77]) and is also often used humorously (along with the camel) to describe something designed by committee. For the "Star Trek: The Next Generation" novel Q-Squared, the titled character claims (in private) to a disbelieving Capt. Picard he personally influenced God's decision to create/evolve the platypus.
The platypus is also a pet in the massively multiplayer online role playing game RuneScape.
"Platypus Man" was a short lived, 1995 sitcom aired on Fox Television and/or UPN in the United States. Fox also had an animated program called "Taz-Mania," featuring the Platypus Bros.: Daniel and Timothy.
In the episode, The Truth in the Myth on Bones, when the team were studying a murdered victim who was supposed to be killed by the cryptic animal, chupacabra, Dr. Saroyan questions the very existence of such a creature, in which intern Nigel-Murray responded, "I'd be skeptical if you told me there was a venomous, egg laying, duck-billed, beaver tailed mammal, and yet the platypus, it does exist."

See also

• Fauna of Australia
• Henry Burrell

Notes

1. ^ Groves, Colin P. (16 November 2005). "Order Monotremata (pp. 1-2)". In Wilson, Don E., and Reeder, DeeAnn M., eds. Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Baltimore: Johns Hopkins University Press, 2 vols. (2142 pp.). p. 2. ISBN 978-0-8018-8221-0. OCLC 62265494. http://www.bucknell.edu/msw3/browse.asp?id=10300020. 
2. ^ ^{a b c} Lunney, D., Dickman, C., Copely, P., Grant, T., Munks, S., Carrick, F., Serena, M. & Ellis, M. (2008). Ornithorhynchus anatinus. In: IUCN 2008. IUCN Red List of Threatened Species. Downloaded on 9 October 2008. D
3. ^ Government of New South Wales (2008). "Symbols & Emblems of NSW". Archived from the original on July 23, 2008. http://web.archive.org/web/20080723133614/http://www.nsw.gov.au/emblems.asp. Retrieved 29 December 2008. 
4. ^ Brian K. Hall (1999-03). "The Paradoxical Platypus". BioScience (American Institute of Biological Sciences) 49 (3): 211–218. doi:10.2307/1313511. JSTOR 1313511. 
5. ^ ^{a b} "Duck-billed Platypus". Museum of hoaxes. http://www.museumofhoaxes.com/hoax/Hoaxipedia/Duckbilled_Platypus/. Retrieved 2010-07-21. 
6. ^ ^{a b c d e f g} "Platypus facts file". Australian Platypus Conservancy. http://www.platypus.asn.au/. Retrieved 2006-09-13. 
7. ^ πλατύπους, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
8. ^ πλατύς, A Greek-English Lexicon, on Perseus
9. ^ πούς, A Greek-English Lexicon, on Perseus
10. ^ Liddell & Scott (1980). Greek-English Lexicon, Abridged Edition. Oxford University Press, Oxford, UK. ISBN 0-19-910207-4. 
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