A frog. (Click here to )
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A frog is a fresh-water amphibian of the family Ranidae, in the Order Anura. They are closely related to toads. The Ranidae are sometimes called the "true frogs" since a few members of other families also have common names including the word "frog."
|Table of contents|
2 Distribution and Status
3 Life cycle
4 A new frog
6 External links
Types and characteristics of frogs
Frogs 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.
Frogs range in size from less than 50mm to 300mm 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: They also have a tympanum on each side of their head, which is involved in sound production. Most frogs have deep, booming calls, or croaks, with some being onomatopoeically represented by the word "ribbet" or "ribbit."
Many species of frog secrete toxins from their skin when under threat. These toxins deter predatory animals from eating them, and some are extremely poisonous to humans. The natives of the Amazon area extract curare from the poison arrow frog.
Distribution and Status
Members 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 and 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.
The life cycle of a frog involves several stages. A female frog lays her eggs 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 an adolescent 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. Furthermore, The red-legged frogs normally reproduce from November to early April because during these months, the water is about six or seven degrees Celsius. Under these cool conditions, embryonic survival is ensured. 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. After about six to fourteen days, the eggs hatch between July and September into brown tadpoles that are about three inches long. The tadpoles then progress to lose their tails, grow legs, and change into a juvenile form with adult characteristics.
A new 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, 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. The BBC have a picture of one