Frog

A common frog

A frog is a member of a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura (Ancient Greek an-, without + oura, tail). The oldest fossil "proto-frog" appeared in the early Triassic of Madagascar, but molecular clock dating suggests their origins may extend further back to 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 rainforests. There are approximately 4,800 recorded species, accounting for over 85% of extant amphibian species. They are also one of the five most diverse vertebrate orders.

Characteristics

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 significantly declining.

Life cycle

A frog begins life as a fertilized egg. A female frog lays a lot of eggs at one time in a pond. The eggs are in a jelly substance that floats on water. The eggs hatch and a tadpole comes out. After about five weeks, the tadpole begins to change. It starts to grow legs and its tail becomes shorter. It also starts to breathe air. This process is called metamorphosis. After this process is complete, the frog is a juvenile, almost an adult. The frog will continue to grow until it is a full adult. The adult frogs then lay their eggs and the cycle starts over.

Classification

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 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 a single central respiratory spiracle and mouthparts consisting of keratinous beaks and denticles.

Frogs and humans

Frogs serve as an important symbol in mythology, literature, and popular culture. They are also considered a keystone species due to their impact on the ecosystem. A decline in frog populations has significant implications. Frogs are also valued as food and also have many cultural roles in literature, symbolism and religion.

See also

• Amphibian
• Tadpole
• Metamorphosis
• Keystone species

External links

• AmphibiaWeb
• IUCN Red List