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59-506: The moss froglet ( Crinia nimbus ) is a species of frog in the family Myobatrachidae . It is endemic to southern Tasmania . Adult males measure 19–27 mm (0.7–1.1 in) and adult females 25–30 mm (1.0–1.2 in) in snout–vent length . The snout is short and projecting. The eyes are prominent. The tympanum is indistinct. The fingers and toes are unwebbed. Dorsal colouration ranges from very dark brown to grey-brown or tan. There are darker markings that are quite obscure in

118-401: A larval stage undergo metamorphosis, and during metamorphosis the organism loses larval characteristics. The word metamorphosis derives from Ancient Greek μεταμόρφωσις , "transformation, transforming", from μετα- ( meta- ), "after" and μορφή ( morphe ), "form". In insects, growth and metamorphosis are controlled by hormones synthesized by endocrine glands near

177-500: A yolk sac ), then to motile larvae (often known as fingerlings due to them roughly reaching the length of a human finger ) that have to forage for themselves after the yolk sac resorbs, and then to the juvenile stage where the fish progressively start to resemble adult morphology and behaviors until finally reaching sexual maturity . In typical amphibian development, eggs are laid in water and larvae are adapted to an aquatic lifestyle. Frogs , toads , and newts all hatch from

236-399: A butterfly 2 – The pupa is now spewing the thread to form chrysalis 3 – The chrysalis is fully formed 4 – Adult butterfly coming out of the chrysalis In cephalochordata , metamorphosis is iodothyronine -induced and it could be an ancestral feature of all chordates . Some fish, both bony fish (Osteichthyes) and jawless fish (Agnatha) , undergo metamorphosis. Fish metamorphosis

295-648: A complete metamorphosis, including a pupal or resting stage between the larval and adult forms. A number of hypotheses have been proposed to explain the evolution of holometaboly from hemimetaboly, mostly centering on whether or not the intermediate stages of hemimetabolous forms are homologous in origin to the pupal stage of holometabolous forms. According to a 2009 study, temperature plays an important role in insect development as individual species are found to have specific thermal windows that allow them to progress through their developmental stages. These windows are not significantly affected by ecological traits, rather,

354-413: A considerable role during physiological processes of multicellular organisms, particularly during embryogenesis , and metamorphosis. Additional research in 2019 found that both autophagy and apoptosis , the two ways programmed cell death occur, are processes undergone during insect metamorphosis. Below is the sequence of steps in the metamorphosis of the butterfly (illustrated): 1 – The larva of

413-528: A diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura (coming from the Ancient Greek ἀνούρα , literally 'without tail'). The oldest fossil "proto-frog" Triadobatrachus is known from the Early Triassic of Madagascar (250   million years ago ), but molecular clock dating suggests their split from other amphibians may extend further back to

472-469: A few feed on plant matter. Frog skin has a rich microbiome which is important to their health. Frogs are extremely efficient at converting what they eat into body mass. They are an important food source for predators and part of the food web dynamics of many of the world's ecosystems . The skin is semi-permeable , making them susceptible to dehydration, so they either live in moist places or have special adaptations to deal with dry habitats. Frogs produce

531-454: A long stage of growth followed by a more gradual metamorphosis to the migrating phase. In the pre-adult freshwater stage, the eel also has phenotypic plasticity because fish-eating eels develop very wide mandibles, making the head look blunt. Leptocephali are common, occurring in all Elopomorpha ( tarpon - and eel -like fish). Most other bony fish undergo metamorphosis initially from egg to immotile larvae known as sac fry ( fry with

590-678: A point of common ancestry. It is based on Frost et al. (2006), Heinicke et al. (2009) and Pyron and Wiens (2011). Leiopelmatidae Ascaphidae Bombinatoridae Alytidae Discoglossidae Pipidae Rhinophrynidae Scaphiopodidae Pelodytidae Pelobatidae Megophryidae Heleophrynidae Sooglossidae Nasikabatrachidae Calyptocephalellidae Myobatrachidae Limnodynastidae Ceuthomantidae Brachycephalidae Eleutherodactylidae Craugastoridae Hemiphractidae Hylidae Bufonidae Aromobatidae Dendrobatidae Leptodactylidae Allophrynidae Metamorphosis Generally organisms with

649-469: A prefrontal bone, presence of a hyoid plate , a lower jaw without teeth (with the exception of Gastrotheca guentheri ) consisting of three pairs of bones (angulosplenial, dentary, and mentomeckelian, with the last pair being absent in Pipoidea ), an unsupported tongue, lymph spaces underneath the skin, and a muscle, the protractor lentis, attached to the lens of the eye . The anuran larva or tadpole has

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708-420: A relatively long, spiral‐shaped gut to digest that diet. Recent studies suggest tadpoles do not have a balanced homeostatic feedback control system until the beginning stages of metamorphosis. At this point, their long gut shortens and begins favoring the diet of insects. Rapid changes in the body can then be observed as the lifestyle of the frog changes completely. The spiral‐shaped mouth with horny tooth ridges

767-466: A single central respiratory spiracle and mouthparts consisting of keratinous beaks and denticles . 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 families of modern frogs, including most common species throughout

826-469: A slightly warty skin and prefers a watery habitat whereas the Panamanian golden frog ( Atelopus zeteki ) is in the toad family Bufonidae and has a smooth skin. The origin of the order name Anura —and its original spelling Anoures —is the Ancient Greek alpha privative prefix ἀν- ( an- from ἀ- before a vowel) 'without', and οὐρά ( ourá ) 'animal tail'. meaning "tailless". It refers to

885-502: A wide range of vocalisations , particularly in their breeding season , and exhibit many different kinds of complex behaviors to attract mates, to fend off predators and to generally survive. Frogs are valued as food by humans and also have many cultural roles in literature, symbolism and religion. They are also seen as environmental bellwethers , with declines in frog populations often viewed as early warning signs of environmental damage. Frog populations have declined significantly since

944-649: Is informal, not from taxonomy or evolutionary history. An adult frog has a stout body, protruding eyes , anteriorly-attached tongue , limbs folded underneath, and no tail (the tail of tailed frogs is an extension of the male cloaca). Frogs have glandular skin, with secretions ranging from distasteful to toxic. Their skin varies in colour from well- camouflaged dappled brown, grey and green to vivid patterns of bright red or yellow and black to show toxicity and ward off predators . Adult frogs live in fresh water and on dry land; some species are adapted for living underground or in trees. Frogs typically lay their eggs in

1003-555: Is iodothyronine-induced and an ancestral feature of all chordates . All three categories of metamorphosis can be found in the diversity of insects, including no metamorphosis ("ametaboly"), incomplete or partial metamorphosis ("hemimetaboly"), and complete metamorphosis ("holometaboly"). While ametabolous insects show very little difference between larval and adult forms (also known as " direct development "), both hemimetabolous and holometabolous insects have significant morphological and behavioral differences between larval and adult forms,

1062-421: Is outside the parental body, development is subject to many adaptations due to specific ecological circumstances. For this reason tadpoles can have horny ridges for teeth, whiskers, and fins. They also make use of the lateral line organ. After metamorphosis, these organs become redundant and will be resorbed by controlled cell death, called apoptosis . The amount of adaptation to specific ecological circumstances

1121-549: Is reabsorbed, due to the higher thyroxin concentrations required for tail resorption. Salamander development is highly diverse; some species go through a dramatic reorganization when transitioning from aquatic larvae to terrestrial adults, while others, such as the axolotl , display pedomorphosis and never develop into terrestrial adults. Within the genus Ambystoma , species have evolved to be pedomorphic several times, and pedomorphosis and complete development can both occur in some species. In newts, metamorphosis occurs due to

1180-402: Is remarkable, with many discoveries still being made. With frogs and toads, the external gills of the newly hatched tadpole are covered with a gill sac after a few days, and lungs are quickly formed. Front legs are formed under the gill sac, and hindlegs are visible a few days later. Following that there is usually a longer stage during which the tadpole lives off a vegetarian diet. Tadpoles use

1239-401: Is resorbed together with the spiral gut. The animal develops a big jaw, and its gills disappear along with its gill sac. Eyes and legs grow quickly, a tongue is formed, and all this is accompanied by associated changes in the neural networks (development of stereoscopic vision, loss of the lateral line system, etc.) All this can happen in about a day. It is not until a few days later that the tail

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1298-524: Is the name of the total group that includes modern frogs in the order Anura as well as their close fossil relatives, the "proto-frogs" or "stem-frogs". The common features possessed by these proto-frogs include 14 presacral vertebrae (modern frogs have eight or 9), a long and forward-sloping ilium in the pelvis , the presence of a frontoparietal bone , and a lower jaw without teeth. The earliest known amphibians that were more closely related to frogs than to salamanders are Triadobatrachus massinoti , from

1357-403: Is typically under strong control by the thyroid hormone. Examples among the non-bony fish include the lamprey . Among the bony fish, mechanisms are varied. The salmon is diadromous , meaning that it changes from a freshwater to a saltwater lifestyle. Many species of flatfish begin their life bilaterally symmetrical , with an eye on either side of the body; but one eye moves to join

1416-647: Is uncertain, but agrees with arguments that it could plausibly derive from a Proto-Indo-European base along the lines of * preu , meaning 'jump'. How Old English frosc gave rise to frogga is, however, uncertain, as the development does not involve a regular sound-change . Instead, it seems that there was a trend in Old English to coin nicknames for animals ending in - g , with examples—themselves all of uncertain etymology—including dog , hog , pig, stag , and (ear)wig . Frog appears to have been adapted from frosc as part of this trend. Meanwhile,

1475-530: The Antarctic Peninsula , indicating that this region was once home to frogs related to those now living in South American Nothofagus forest . A cladogram showing the relationships of the different families of frogs in the clade Anura can be seen in the table below. This diagram, in the form of a tree , shows how each frog family is related to other families, with each node representing

1534-719: The Cretaceous–Paleogene extinction event associated with the Chicxulub impactor . All origins of arboreality (e.g. in Hyloidea and Natatanura) follow from that time and the resurgence of forest that occurred afterwards. Frog fossils have been found on all of the Earth's continents. In 2020, it was announced that 40 million year old helmeted frog fossils had been discovered by a team of vertebrate palaeontologists in Seymour Island on

1593-469: The Permian , 265   million years ago. Frogs are widely distributed, ranging from the tropics to subarctic regions, but the greatest concentration of species diversity is in tropical rainforest . Frogs account for around 88% of extant amphibian species. They are also one of the five most diverse vertebrate orders. Warty frog species tend to be called toads , but the distinction between frogs and toads

1652-548: The Permian , rather less than 300 million years ago, a date in better agreement with the palaeontological data. A further study in 2011 using both extinct and living taxa sampled for morphological, as well as molecular data, came to the conclusion that Lissamphibia is monophyletic and that it should be nested within Lepospondyli rather than within Temnospondyli . The study postulated that Lissamphibia originated no earlier than

1711-519: The divergence of the three groups took place in the Paleozoic or early Mesozoic before the break-up of the supercontinent Pangaea and soon after their divergence from the lobe-finned fishes . This would help account for the relative scarcity of amphibian fossils from the period before the groups split. Another molecular phylogenetic analysis conducted about the same time concluded that lissamphibians first appeared about 330 million years ago and that

1770-623: The edible frog ( Pelophylax esculentus ) is a hybrid between the pool frog ( P. lessonae ) and the marsh frog ( P. ridibundus ). The fire-bellied toads Bombina bombina and B. variegata are similar in forming hybrids. These are less fertile than their parents, giving rise to a hybrid zone where the hybrids are prevalent. The origins and evolutionary relationships between the three main groups of amphibians are hotly debated. A molecular phylogeny based on rDNA analysis dating from 2005 suggests that salamanders and caecilians are more closely related to each other than they are to frogs and

1829-425: The middle Jurassic is slightly younger, about 155–170 million years old. The main evolutionary changes in this species involved the shortening of the body and the loss of the tail. Tadpoles of N. degiustoi constitute the oldest tadpoles found as of 2024, dating back to 168-161 million years ago. These tadpoles also showed adaptations for filter-feeding , implying residence in temporary pools by filter-feeding larvae

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1888-429: The richest in species . The Anura include all modern frogs and any fossil species that fit within the anuran definition. The characteristics of anuran adults include: 9 or fewer presacral vertebrae, the presence of a urostyle formed of fused vertebrae, no tail, a long and forward-sloping ilium, shorter fore limbs than hind limbs, radius and ulna fused, tibia and fibula fused, elongated ankle bones , absence of

1947-540: The temnospondyl-origin hypothesis is more credible than other theories. The neobatrachians seemed to have originated in Africa/India, the salamanders in East Asia and the caecilians in tropical Pangaea. Other researchers, while agreeing with the main thrust of this study, questioned the choice of calibration points used to synchronise the data. They proposed that the date of lissamphibian diversification should be placed in

2006-412: The 1950s. More than one third of species are considered to be threatened with extinction and over 120 are believed to have become extinct since the 1980s. The number of malformations among frogs is on the rise and an emerging fungal disease, chytridiomycosis , has spread around the world. Conservation biologists are working to understand the causes of these problems and to resolve them. The use of

2065-519: The anuran lineage proper all lived in the early Jurassic period. One such early frog species, Prosalirus bitis , was discovered in 1995 in the Kayenta Formation of Arizona and dates back to the Early Jurassic epoch (199.6 to 175 million years ago), making Prosalirus somewhat more recent than Triadobatrachus . Like the latter, Prosalirus did not have greatly enlarged legs, but had

2124-411: The change in habitat, not a change in diet, because newt larvae already feed as predators and continue doing so as adults. Newts' gills are never covered by a gill sac and will be resorbed only just before the animal leaves the water. Adults can move faster on land than in water. Newts often have an aquatic phase in spring and summer, and a land phase in winter. For adaptation to a water phase, prolactin

2183-540: The common names frog and toad has no taxonomic justification. From a classification 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 and have smooth, moist skins; the term toad generally refers to species that are terrestrial with dry, warty skins. There are numerous exceptions to this rule. The European fire-bellied toad ( Bombina bombina ) has

2242-513: The darkest-coloured specimens. Some individuals have a pale or tan mid-vertebral stripe. Ventral surfaces are dark brown with fine white spots or pale with dark spots. The male advertisement call is a series of tok' s, likened to a ping-pong ball being dropped on wood. Crinia nimbus is the only fully terrestrial frog in Tasmania. They live in moist, cool, alpine habitats, poorly drained sites in moor land (shrubland and heath), and rainforest, from

2301-462: The development of adult characteristics during ecdysis . In holometabolous insects, molts between larval instars have a high level of juvenile hormone, the moult to the pupal stage has a low level of juvenile hormone, and the final, or imaginal , molt has no juvenile hormone present at all. Experiments on firebugs have shown how juvenile hormone can affect the number of nymph instar stages in hemimetabolous insects. In chordates, metamorphosis

2360-474: The early Triassic period of Madagascar (about 250 million years ago), and Czatkobatrachus polonicus , from the Early Triassic of Poland (about the same age as Triadobatrachus ). The skull of Triadobatrachus is frog-like, being broad with large eye sockets, but the fossil has features diverging from modern frogs. These include a longer body with more vertebrae . The tail has separate vertebrae unlike

2419-538: The eggs as larvae with external gills but it will take some time for the amphibians to interact outside with pulmonary respiration. Afterwards, newt larvae start a predatory lifestyle, while tadpoles mostly scrape food off surfaces with their horny tooth ridges. Metamorphosis in amphibians is regulated by thyroxin concentration in the blood, which stimulates metamorphosis, and prolactin , which counteracts its effect. Specific events are dependent on threshold values for different tissues. Because most embryonic development

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2478-650: The evolution of metamorphosis in insects is thought to have fuelled their dramatic radiation (1,2). Some early ametabolous "true insects" are still present today, such as bristletails and silverfish . Hemimetabolous insects include cockroaches , grasshoppers , dragonflies , and true bugs . Phylogenetically, all insects in the Pterygota undergo a marked change in form, texture and physical appearance from immature stage to adult. These insects either have hemimetabolous development, and undergo an incomplete or partial metamorphosis, or holometabolous development, which undergo

2537-411: The front of the body ( anterior ). Neurosecretory cells in an insect's brain secrete a hormone, the prothoracicotropic hormone (PTTH) that activates prothoracic glands, which secrete a second hormone, usually ecdysone (an ecdysteroid ), that induces ecdysis (shedding of the exoskeleton). PTTH also stimulates the corpora allata , a retrocerebral organ, to produce juvenile hormone , which prevents

2596-518: The fused urostyle or coccyx in modern frogs. The tibia and fibula bones are also separate, making it probable that Triadobatrachus was not an efficient leaper. A 2019 study has noted the presence of Salientia from the Chinle Formation , and suggested that anurans might have first appeared during the Late Triassic . On the basis of fossil evidence, the earliest known "true frogs" that fall into

2655-477: The late Carboniferous , some 290 to 305 million years ago. The split between Anura and Caudata was estimated as taking place 292 million years ago, rather later than most molecular studies suggest, with the caecilians splitting off 239 million years ago. In 2008, Gerobatrachus hottoni , a temnospondyl with many frog- and salamander-like characteristics, was discovered in Texas . It dated back 290 million years and

2714-566: The most significant being the inclusion, in holometabolous organisms, of a pupal or resting stage between the larval and adult forms. In hemimetabolous insects , immature stages are called nymphs . Development proceeds in repeated stages of growth and ecdysis (moulting); these stages are called instars . The juvenile forms closely resemble adults, but are smaller and lack adult features such as wings and genitalia. The size and morphological differences between nymphs in different instars are small, often just differences in body proportions and

2773-415: The nest after completing the metamorphosis , about one year after starting their development. Crinia nimbus is probably widespread in southwestern Tasmania. There are no know threats to it, although the terrestrial nests are vulnerable to trampling by animals and people (tourists and researchers alike). Most of the range is protected by national parks. Frog See text A frog is any member of

2832-478: The nineteenth century, and is paralleled widely in other Germanic languages , with examples in the modern languages including German Frosch , Norwegian frosk , Icelandic froskur , and Dutch (kik)vors . These words allow reconstruction of a Common Germanic ancestor * froskaz . The third edition of the Oxford English Dictionary finds that the etymology of * froskaz

2891-488: The number of segments; in later instars, external wing buds form. The period from one molt to the next is called a stadium. In holometabolous insects, immature stages are called larvae and differ markedly from adults. Insects which undergo holometabolism pass through a larval stage, then enter an inactive state called pupa (called a "chrysalis " in butterfly species), and finally emerge as adults. The earliest insect forms showed direct development ( ametabolism ), and

2950-464: The other side of the fish – which becomes the upper side – in the adult form. The European eel has a number of metamorphoses, from the larval stage to the leptocephalus stage, then a quick metamorphosis to glass eel at the edge of the continental shelf (eight days for the Japanese eel ), two months at the border of fresh and salt water where the glass eel undergoes a quick metamorphosis into elver, then

3009-458: The sea level to 1,287 m (4,222 ft). They are mostly quite cryptic and hide in vegetation and in the nest cavities, but males can be heard calling in spring to summer. Females lay clutches of 4–16 egg in nests in moss, lichen, or peat. The larvae hatch inside egg capsules. After a while, egg capsules disintegrate, but the larvae continue their development in the resulting gelatinous mass as free-living, but non-feeding larvae. They only leave

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3068-533: The tailless character of these amphibians. The origins of the word frog are uncertain and debated. The word is first attested in Old English as frogga , but the usual Old English word for the frog was frosc (with variants such as frox and forsc ), and it is agreed that the word frog is somehow related to this. Old English frosc remained in dialectal use in English as frosh and frosk into

3127-428: The typical three-pronged pelvic structure of modern frogs. Unlike Triadobatrachus , Prosalirus had already lost nearly all of its tail and was well adapted for jumping. Another Early Jurassic frog is Vieraella herbsti , which is known only from dorsal and ventral impressions of a single animal and was estimated to be 33 mm ( 1 + 1 ⁄ 4  in) from snout to vent. Notobatrachus degiustoi from

3186-467: The water. The eggs hatch into aquatic larvae called tadpoles that have tails and internal gills . They have highly specialised rasping mouth parts suitable for herbivorous , omnivorous or planktivorous diets. The life cycle is completed when they metamorphose into adults. A few species deposit eggs on land or bypass the tadpole stage. Adult frogs generally have a carnivorous diet consisting of small invertebrates , but omnivorous species exist and

3245-529: The windows are phylogenetically adapted to the ecological circumstances insects are living in. According to research from 2008, adult Manduca sexta is able to retain behavior learned as a caterpillar . Another caterpillar, the ornate moth caterpillar , is able to carry toxins that it acquires from its diet through metamorphosis and into adulthood, where the toxins still serve for protection against predators. Many observations published in 2002, and supported in 2013 indicate that programmed cell death plays

3304-543: The word toad , first attested as Old English tādige , is unique to English and is likewise of uncertain etymology. It is the basis for the word tadpole , first attested as Middle English taddepol , apparently meaning 'toad-head'. About 88% of amphibian species are classified in the order Anura. These include over 7,700 species in 59 families , of which the Hylidae (1062 spp.), Strabomantidae (807 spp.), Microhylidae (758 spp.), and Bufonidae (657 spp.) are

3363-438: The world. The suborder Neobatrachia is further divided into the two superfamilies Hyloidea and Ranoidea . 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. Some species of anurans hybridise readily. For instance,

3422-540: Was already commonplace. The evolution of modern Anura likely was complete by the Jurassic period. Since then, evolutionary changes in chromosome numbers have taken place about 20 times faster in mammals than in frogs, which means speciation is occurring more rapidly in mammals. According to genetic studies, the families Hyloidea , Microhylidae , and the clade Natatanura (comprising about 88% of living frogs) diversified simultaneously some 66 million years ago, soon after

3481-473: Was hailed as a missing link , a stem batrachian close to the common ancestor of frogs and salamanders, consistent with the widely accepted hypothesis that frogs and salamanders are more closely related to each other (forming a clade called Batrachia) than they are to caecilians. However, others have suggested that Gerobatrachus hottoni was only a dissorophoid temnospondyl unrelated to extant amphibians. Salientia (Latin salire ( salio ), "to jump")

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