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Frog |
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Frog Frogs are amphibians in the Order Anura, which includes frogs and toads. Frogs look like toads, but are generally more slender and have a less warty skin. The true frogs are the Ranidae. The term "frog" has no meaning whatsoever in animal systematics, since many anuran families include both "frogs" and "toads". Types of frogsFrogs are a diverse group with some 4800 species. Most spend their lives in or near a source of water (water frogs), although tree frogs live in moist environments that are not actually aquatic. The requirement for water becomes most acute for egg and tadpole stages of the frog, yet here again some species are able to utilize temporary pools and water collected in the axils of plants. The most familiar frog families are the true frogs Ranidae (common frog, bullfrog, edible frog, green frog, leopard frog), the Dendrobatids like the poison dart frogs and the tree frogs Hylidae. A classification of anurans based on "frogs" and "toads" results in polyphyletic groups. For example, the Discoglossidae includes both "frogs" and "toads": midwife toads, fire-bellied toads and painted frogs, although fire-bellied toads are now classified in the Bombinatoridae.
CharacteristicsFrogs range in size from less than 50mm (2.0 in) to 300mm (11.8 in) in Conraua goliath, which is the largest known frog. All frogs have horizontal pupils, smooth skin and long legs with webbing between their toes. This family has a bicornuated tongue that is attached in front. Frogs have three eyelid membranes: one transparent, for protecting the eyes underwater, and two which are translucent to opaque, like human eyelids. They also have a tympanum on each side of their head, which is involved in hearing. Many species of frogs have deep calls, or croaks. Frog noise tends to be spelt (for Engllish speakers) as "crrrrk" in Britain and "ribbit" in the USA: this difference may be due to Britain and the USA having different species of frogs; the croak of the bullfrog is sometimes spelt "jug o' rum". The Ancient Greeks (for example Aristophanes) transcribed the croak of the usual Greek species of frog as "korax" or "brekekekex co-ax co-ax". Small tropical frogs tend to have higher-pitched calls. Some species of frog secrete toxins from their skin. These toxins deter predatory animals from eating them, and some are extremely poisonous to humans. Some natives of the Amazon area extract arrow-poison from the poison dart frog. Distribution and StatusMembers of this family are found worldwide, but they have a limited distribution in South America and Australia. They do not occur in the West Indies, nor on most oceanic islands. In many parts of the world the frog population has declined drastically over the last few decades. Pollutants are one cause for this decline, but other culprits include climatic changes, parasitic infestation, introduction of non-indigenous predators/competitors, infectious diseases, and urban encroachment. Life cycleThe life cycle of a frog involves several stages. Typically adult frogs gather in suitable pools, the first to arive usually being the males. Their croaking may well encourage the females to arrive. A female would wish to avoid arriving at a pond which did not have any males in attendance. Gravid female frogs are actively and persistently sought out by males and many males will often try to attach themselves to a single female but eventually one male will secure possession. Amplexus is the process wherein the male grasps the female while she lays her eggs. At the same time, he fertilizes them with a fluid containing sperm. The eggs are about 2.0 to 2.8 millimetres in diameter and are dark brown and are covered in an outer shell of gelatinous transparent material which swells in contact with water. The female frog lays her eggss in a shallow pond or creek, where they will be sheltered from the current and from predators. The eggs, known as frogspawn hatch into tadpoles. The tadpole stage develops gradually into a froglet, resembling an adult but retaining a vestigial tail. Finally the froglet develops into an adult frog. Typically, tadpoles are herbivores, feeding mostly on algae, whereas juvenile and adult frogs are rather voracious carnivores. Most temperate species of frog reproduce in the period between late autumn to 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 and 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. Diet Most frogs eat insects such as mosquitoes, earthworms and small fish such as minnows; however, a few of the bigger ones may tackle larger prey, such as mice. Some frogs use their sticky tongues effectively in catching fast-moving prey. Still others capture their prey in their mouth with speed and agility. They hunt mostly at night. A new frogMain article: Purple Frog In 2003, Franky Bossuyt of the Vrije Universiteit Brussel (Free University of Brussels) and S.D. Biji of the Tropical Botanic Garden and Research Institute in Palode, India reported the discovery of a new species of frog so distinct in appearance and DNA that it merited its own new family, the first new family for frogs since 1926. This new species, dubbed Nasikabatrachus sahyadrensis (commonly Purple Frog or Pignose Frog), is dark purple in color, seven centimeters in length, and has a small head and a pointy snout. Genetically, its closest living relatives are the sooglossids found in the Seychelles. The new species was discovered in the Sahyadri (Western Ghats) Mountains in India.
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