Amphibians are ectothermic, tetrapod vertebrates of the class Amphibia. Modern amphibians are all Lissamphibia, they inhabit a wide variety of habitats, with most species living within terrestrial, arboreal or freshwater aquatic ecosystems. Thus amphibians start out as larvae living in water, but some species have developed behavioural adaptations to bypass this; the young undergo metamorphosis from larva with gills to an adult air-breathing form with lungs. Amphibians use their skin as a secondary respiratory surface and some small terrestrial salamanders and frogs lack lungs and rely on their skin, they are superficially similar to lizards but, along with mammals and birds, reptiles are amniotes and do not require water bodies in which to breed. With their complex reproductive needs and permeable skins, amphibians are ecological indicators; the earliest amphibians evolved in the Devonian period from sarcopterygian fish with lungs and bony-limbed fins, features that were helpful in adapting to dry land.
They diversified and became dominant during the Carboniferous and Permian periods, but were displaced by reptiles and other vertebrates. Over time, amphibians shrank in size and decreased in diversity, leaving only the modern subclass Lissamphibia; the three modern orders of amphibians are Anura and Apoda. The number of known amphibian species is 8,000, of which nearly 90% are frogs; the smallest amphibian in the world is a frog from New Guinea with a length of just 7.7 mm. The largest living amphibian is the 1.8 m Chinese giant salamander, but this is dwarfed by the extinct 9 m Prionosuchus from the middle Permian of Brazil. The study of amphibians is called batrachology, while the study of both reptiles and amphibians is called herpetology; the word "amphibian" is derived from the Ancient Greek term ἀμφίβιος, which means "both kinds of life", ἀμφί meaning "of both kinds" and βιος meaning "life". The term was used as a general adjective for animals that could live on land or in water, including seals and otters.
Traditionally, the class Amphibia includes all tetrapod vertebrates. Amphibia in its widest sense was divided into three subclasses, two of which are extinct: Subclass Lepospondyli† Subclass Temnospondyli† Subclass Lissamphibia Salientia: Jurassic to present—6,200 current species in 53 families Caudata: Jurassic to present—652 current species in 9 families Gymnophiona: Jurassic to present—192 current species in 10 families The actual number of species in each group depends on the taxonomic classification followed; the two most common systems are the classification adopted by the website AmphibiaWeb, University of California and the classification by herpetologist Darrel Frost and the American Museum of Natural History, available as the online reference database "Amphibian Species of the World". The numbers of species cited above follows Frost and the total number of known amphibian species as of March 31, 2019 is 8,000, of which nearly 90% are frogs. With the phylogenetic classification, the taxon Labyrinthodontia has been discarded as it is a polyparaphyletic group without unique defining features apart from shared primitive characteristics.
Classification varies according to the preferred phylogeny of the author and whether they use a stem-based or a node-based classification. Traditionally, amphibians as a class are defined as all tetrapods with a larval stage, while the group that includes the common ancestors of all living amphibians and all their descendants is called Lissamphibia; the phylogeny of Paleozoic amphibians is uncertain, Lissamphibia may fall within extinct groups, like the Temnospondyli or the Lepospondyli, in some analyses in the amniotes. This means that advocates of phylogenetic nomenclature have removed a large number of basal Devonian and Carboniferous amphibian-type tetrapod groups that were placed in Amphibia in Linnaean taxonomy, included them elsewhere under cladistic taxonomy. If the common ancestor of amphibians and amniotes is included in Amphibia, it becomes a paraphyletic group. All modern amphibians are included in the subclass Lissamphibia, considered a clade, a group of species that have evolved from a common ancestor.
The three modern orders are Anura and Gymnophiona. It has been suggested that salamanders arose separately from a Temnospondyl-like ancestor, that caecilians are the sister group of the advanced reptiliomorph amphibians, thus of amniotes. Although the fossils of several older proto-frogs with primitive characteristics are known, the oldest "true frog" is Prosalirus bitis, from the Early Jurassic Kayenta Formation of Arizona, it is anatomically similar to modern frogs. The oldest known caecilian is another Early Jurassic species, Eocaecilia micropodia from Arizona; the earliest salamander is Beiyanerpeton jianpingensis from the Late Jurassic of northeastern China. Authorities disagree as to whether Salientia is a superorder that includes the order Anura, or whether
The Bombinatoridae are referred to as fire-bellied toads because of their brightly colored ventral sides, which show they are toxic. This family includes two genera and Bombina, both of which have flattened bodies. Bombina species are warty, aquatic toads about 7 cm in length, most noted for their bright bellies, they display the unken reflex when disturbed. This acts as a warning to predators; the vocal behavior of some Bombina species are unusual in that the call is produced during inhalation rather than exhalation as in other frogs. They lay pigmented eggs in ponds. Barbourula species occur in the Philippine Islands and Borneo, while Bombina species are found throughout Eurasia, they are less colored than Bombina, possess webbed fingers in addition to webbed toes. Characteristics of tadpoles of Barbourula are unknown. Barbourula was considered to be situated intermediate between Discoglossus and Bombina, but closer to the latter, so was added to the Bombinatoridae when that family was split from the Discoglossidae.
Fossil Bombina specimens are known from the Pliocene to the Pleistocene. The earliest fossil specimens are Eobarbourula from the Eocene of India, Hatzegobatrachus from Late Cretaceous of Hateg island, Romania Family Bombinatoridae Genus Barbourula - Jungle Toads Barbourula busuangensis - Philippine flat-headed frog or Busuanga jungle toad Barbourula kalimantanensis - Bornean flat-headed frog or Kalimantan jungle toad Genus Bombina - Firebelly Toads Bombina bombina – fire-bellied toad Bombina maxima – Yunnan firebelly toad or large-webbed bell toad Bombina microdeladigitora – Hubei firebelly toad or small-webbed bell toad Bombina fortinuptialis – large-spined bell toad or Guangxi firebelly toad, now considered a synonym of B. microdeladigitora Bombina lichuanensis – Lichuan bell toad, now considered a synonym of B. microdeladigitora Bombina orientalis – Oriental fire-bellied toad Bombina pachypus – Apennine yellow-bellied toad Bombina variegata – yellow-bellied toad San Mauro, Diego. "Phylogenetic relationships of discoglossid frogs based on complete mitochondrial genomes and nuclear genes".
Gene. 343: 357–66. Doi:10.1016/j.gene.2004.10.001. PMID 15588590. San Mauro, Diego. "Initial diversification of living amphibians predated the breakup of Pangaea". American Naturalist. 165: 590–9. Doi:10.1086/429523. PMID 15795855
The Pipidae are a family of primitive, tongueless frogs. The 41 species in the family Pipidae are found in tropical South sub-Saharan Africa; these frogs are aquatic and have numerous morphological modifications befitting their habitat. For example, the feet are webbed, the body is flattened, a lateral line system is present. In addition, pipids possess modified ears for producing and receiving sound underwater, they lack vocal cords, instead having bony rods in the larynx that help produce sound. They range from 4 to 19 cm in body length; the fossil record for pipids is good, with 12 extinct species known. Six of these are placed in the remainder in extinct genera; these fossils are known from Africa, South America, the Middle East back to the Lower Cretaceous. Family Pipidae Gray, 1825 Hymenochirus Boulenger, 1896 - dwarf clawed frogs Pipa Laurenti, 1768 - Surinam toads Pseudhymenochirus Chabanaud, 1920- Merlin's dwarf gray frog or Merlin's clawed frog Xenopus Wagler, 1827 - clawed frogs Subgenus Silurana Wagler, 1827 - common clawed frogs Subgenus Xenopus Gray, 1864 - tropical clawed frogs Data related to Pipidae at Wikispecies Media related to Pipidae at Wikimedia Commons
Animals are multicellular eukaryotic organisms that form the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, grow from a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. Animals range in length from 8.5 millionths of a metre to 33.6 metres and have complex interactions with each other and their environments, forming intricate food webs. The category includes humans, but in colloquial use the term animal refers only to non-human animals; the study of non-human animals is known as zoology. Most living animal species are in the Bilateria, a clade whose members have a bilaterally symmetric body plan; the Bilateria include the protostomes—in which many groups of invertebrates are found, such as nematodes and molluscs—and the deuterostomes, containing the echinoderms and chordates.
Life forms interpreted. Many modern animal phyla became established in the fossil record as marine species during the Cambrian explosion which began around 542 million years ago. 6,331 groups of genes common to all living animals have been identified. Aristotle divided animals into those with those without. Carl Linnaeus created the first hierarchical biological classification for animals in 1758 with his Systema Naturae, which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa and the Protozoa, single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics, which are effective at demonstrating the evolutionary relationships between animal taxa. Humans make use of many other animal species for food, including meat and eggs. Dogs have been used in hunting, while many aquatic animals are hunted for sport.
Non-human animals have appeared in art from the earliest times and are featured in mythology and religion. The word "animal" comes from the Latin animalis, having soul or living being; the biological definition includes all members of the kingdom Animalia. In colloquial usage, as a consequence of anthropocentrism, the term animal is sometimes used nonscientifically to refer only to non-human animals. Animals have several characteristics. Animals are eukaryotic and multicellular, unlike bacteria, which are prokaryotic, unlike protists, which are eukaryotic but unicellular. Unlike plants and algae, which produce their own nutrients animals are heterotrophic, feeding on organic material and digesting it internally. With few exceptions, animals breathe oxygen and respire aerobically. All animals are motile during at least part of their life cycle, but some animals, such as sponges, corals and barnacles become sessile; the blastula is a stage in embryonic development, unique to most animals, allowing cells to be differentiated into specialised tissues and organs.
All animals are composed of cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. During development, the animal extracellular matrix forms a flexible framework upon which cells can move about and be reorganised, making the formation of complex structures possible; this may be calcified, forming structures such as shells and spicules. In contrast, the cells of other multicellular organisms are held in place by cell walls, so develop by progressive growth. Animal cells uniquely possess the cell junctions called tight junctions, gap junctions, desmosomes. With few exceptions—in particular, the sponges and placozoans—animal bodies are differentiated into tissues; these include muscles, which enable locomotion, nerve tissues, which transmit signals and coordinate the body. There is an internal digestive chamber with either one opening or two openings. Nearly all animals make use of some form of sexual reproduction, they produce haploid gametes by meiosis.
These fuse to form zygotes, which develop via mitosis into a hollow sphere, called a blastula. In sponges, blastula larvae swim to a new location, attach to the seabed, develop into a new sponge. In most other groups, the blastula undergoes more complicated rearrangement, it first invaginates to form a gastrula with a digestive chamber and two separate germ layers, an external ectoderm and an internal endoderm. In most cases, a third germ layer, the mesoderm develops between them; these germ layers differentiate to form tissues and organs. Repeated instances of mating with a close relative during sexual reproduction leads to inbreeding depression within a population due to the increased prevalence of harmful recessive traits. Animals have evolved numerous mechanisms for avoiding close inbreeding. In some species, such as the splendid fairywren, females benefit by mating with multiple males, thus producing more offspring of higher genetic quality; some animals are capable of asexual reproduction, which results
Tetrapods are four-limbed animals constituting the superclass Tetrapoda. It includes existing and extinct amphibians and mammals. Tetrapods evolved from a group of animals known as the Tetrapodomorpha which, in turn, evolved from ancient Sarcopterygii around 390 million years ago in the middle Devonian period; the first tetrapods appeared by the late Devonian, 367.5 million years ago. The change from a body plan for breathing and navigating in water to a body plan enabling the animal to move on land is one of the most profound evolutionary changes known; the first tetrapods were aquatic. Modern amphibians, which evolved from earlier groups, are semiaquatic. However, most tetrapod species today are amniotes, most of those are terrestrial tetrapods whose branch evolved from earlier tetrapods about 340 million years ago; the key innovation in amniotes over amphibians is laying of eggs on land or having further evolved to retain the fertilized egg within the mother. Amniote tetrapods drove most amphibian tetrapods to extinction.
One group of amniotes diverged into the reptiles, which includes lepidosaurs, crocodilians and extinct relatives. Amniotes include the tetrapods that further evolved for flight—such as birds from among the dinosaurs, bats from among the mammals; some tetrapods, such as the snakes, have lost some or all of their limbs through further speciation and evolution. Others, such as amphibians, returned to or aquatic lives, the first during the Carboniferous period. Tetrapods have numerous anatomical and physiological features that are distinct from their aquatic ancestors; these include the structure of the jaw and teeth for feeding on land, limb girdles and extremities for land locomotion, lungs for respiration in air, a heart for circulation, eyes and ears for seeing and hearing in air. Tetrapods can be defined in cladistics as the nearest common ancestor of all living amphibians and all living amniotes, along with all of the descendants of that ancestor; this is a node-based definition. The group so defined is crown tetrapods.
The term tetrapodomorph is used for the stem-based definition: any animal, more related to living amphibians, reptiles and mammals than to living dipnoi. The group so defined is known as the tetrapod total group. Stegocephalia is a larger group equivalent to some broader uses of the word tetrapod, used by scientists who prefer to reserve tetrapod for the crown group; such scientists use the term "stem-tetrapod" to refer to those tetrapod-like vertebrates that are not members of the crown group, including the tetrapodomorph fishes. The two subclades of crown tetrapods are Reptiliomorpha. Batrachomorphs are all animals sharing a more recent common ancestry with living amphibians than with living amniotes. Reptiliomorphs are all animals sharing a more recent common ancestry with living amniotes than with living amphibians. Tetrapoda includes four living classes: amphibians, reptiles and birds. Overall, the biodiversity of lissamphibians, as well as of tetrapods has grown exponentially over time. However, that diversification process was interrupted at least a few times by major biological crises, such as the Permian–Triassic extinction event, which at least affected amniotes.
The overall composition of biodiversity was driven by amphibians in the Palaeozoic, dominated by reptiles in the Mesozoic and expanded by the explosive growth of birds and mammals in the Cenozoic. As biodiversity has grown, so has the number of niches that tetrapods have occupied; the first tetrapods were aquatic and fed on fish. Today, the Earth supports a great diversity of tetrapods that live in many habitats and subsist on a variety of diets; the following table shows summary estimates for each tetrapod class from the IUCN Red List of Threatened Species, 2014.3, for the number of extant species that have been described in the literature, as well as the number of threatened species. The classification of tetrapods has a long history. Traditionally, tetrapods are divided into four classes based on gross anatomical and physiological traits. Snakes and other legless reptiles are considered tetrapods because they are sufficiently like other reptiles that have a full complement of limbs. Similar considerations apply to aquatic mammals.
Newer taxonomy is based on cladistics instead, giving a variable number of major "branches" of the tetrapod family tree. As is the case throughout evolutionary biology today, there is debate over how to properly classify the groups within Tetrapoda. Traditional biological classification sometimes fa
A tadpole is the larval stage in the life cycle of an amphibian that of a frog or toad. They are wholly aquatic, though some species have tadpoles that are terrestrial; when first hatched from the egg they have a more or less globular body, a laterally compressed tail and internal or external gills. As they grow they undergo metamorphosis, during which process they grow limbs, develop lungs and reabsorb the tail. Most tadpoles are herbivorous and during metamorphosis the mouth and internal organs are rearranged to prepare for an adult carnivorous lifestyle. Having no hard parts, it might be expected. However, traces of biofilms have been preserved and fossil tadpoles have been found dating back to the Miocene. Tadpoles are eaten in some parts of the world and are mentioned in folk tales and used as a symbol in ancient Egyptian numerals; the name "tadpole" is from Middle English taddepol, made up of the elements tadde, "toad", pol, "head". "pollywog" / "polliwog" is from Middle English polwygle, made up of the same pol, "head", wiglen, "to wiggle".
Tadpoles are young amphibians that live in the water, though a few tadpoles are semi-terrestrial and terrestrial. During the tadpole stage of the amphibian life cycle, most respire by means of autonomous external or internal gills, they do not have arms or legs until the transition to adulthood, have a large, flattened tail with which they swim by lateral undulation, similar to most fish. As a tadpole matures, it most metamorphosizes by growing limbs and outwardly absorbing its tail by apoptosis. Lungs develop around the time of leg development, tadpoles late in development will be found near the surface of the water, where they breathe air. During the final stages of external metamorphosis, the tadpole's mouth changes from a small, enclosed mouth at the front of the head to a large mouth the same width as the head; the intestines shorten to accommodate the new diet. Most tadpoles are herbivorous; some species are omnivorous. Tadpoles vary in size, both during their development and between species.
For example, in a single family, length of late-stage tadpoles varies between 33 millimetres and 106 millimetres. The tadpoles of Pseudis paradoxa grow to the largest of any frog. Despite their soft-bodied nature and lack of mineralised hard parts, fossil tadpoles have been recovered from Upper Miocene strata, they are preserved with more robust structures preserved as a carbon film. In Miocene fossils from Libros, the brain case is preserved in calcium carbonate, the nerve cord in calcium phosphate. Other parts of the tadpoles' bodies exist as organic remains and bacterial biofilms, with sedimentary detritus present in the gut. Tadpole remains with telltale external gills are known from several labyrinthodont groups; some tadpoles are used as food. Tadpoles of megophryid frog Oreolalax rhodostigmatus are large, more than 10 cm in length, are collected for human consumption in China. In India, Clinotarsus curtipes are collected for food, in Peru at least Telmatobius mayoloi tadpoles are collected for food and medicine.
According to Sir George Scott, in the origin myths of the Wa people in China and Myanmar, the first Wa originated from two female ancestors Ya Htawm and Ya Htai, who spent their early phase as tadpoles in a lake in the Wa country known as Nawng Hkaeo. In the Ancient Egyptian numerals, a hieroglyphic representing a tadpole was used to denote the value of 100,000. McDiarmid, Roy W.. Tadpoles: the Biology of Anuran Larvae. Chicago: University of Chicago Press. ISBN 0226557634
Phrynopus is a genus of frogs of the Craugastoridae family. Their common name is Andes frogs, they are endemic to Peru and inhabit the upper humid montane forests and supra-treeline grasslands in the Cordillera Oriental, with one record from the Peruvian Cordillera Occidental. The contents and phylogenetic position of Phrynopus have long been uncertain, species once included in this genus have been moved to other genera. Hedges and colleagues placed it in 2008 in Strabomantidae, subfamily Strabomantinae. Most the genus was transferred into Craugastoridae, subfamily Holoadeninae. However, the AmphibiaWeb keeps Noblella in Strabomantidae/Strabomantinae, a family/subfamily no longer recognized by the Amphibian Species of the World. Phrynopus are small to medium-sized frogs, from 14.5 mm snout–vent length in Phrynopus auriculatus to 54 mm in Phrynopus kauneorum. Head is narrower than the body. Differentiated tympanic membrane and tympanic annulus are absent, except in Phrynopus auriculatus and Phrynopus peruanus, two basal species.
Dorsum is smooth to pustulate. Venter is areolate. There are 26 species in this genus