free download PNG images :Frog

Frogs are the majority members of the various short-lived, tailless amphibians that make up the Anura sequence. The oldest fossil "primitive frog" appeared in the Early Triassic of Madagascar, but the age of molecular clock indicates that their origin may extend to the Permian of 265 million years ago. Frogs are widely distributed from the tropics to the sub Arctic, but the areas with the most species diversity are tropical rainforests. About 4800 species have been recorded, accounting for more than 85% of the existing amphibian species. They are also one of the five most diverse vertebrate populations.

The body plan of adult frogs is usually characterized by a strong body, protruding eyes, split tongue, folded limbs below and no tail in adulthood. In addition to living in fresh water and dry land, adults of some species are also suitable for living underground or in trees. Frog's skin is a gland, secretions from harmful to toxic. Frog wart species are often called toads, but the difference between frogs and toads is based on informal naming conventions that focus on warts rather than taxonomic or evolutionary history. Some toads are more closely related to frogs than others. Frogs' skin colors range from vivid patterns disguised as mottled brown, gray and green to bright red, yellow and black to promote toxicity and warn natural enemies.

Frogs usually lay their eggs in the water. The eggs hatch into an aquatic larva called T. have a tail and internal G. They have highly specialized rough parts, suitable for herbivores, omnivores or floating food. When they become adults, the life cycle is complete. A few species lay their eggs on land or bypass the stage. Adult frogs usually eat carnivorous food, including small invertebrates, but omnivorous species exist and eat fruit. Frogs are very effective at turning food they eat into weight. They are important food sources for predators and are part of the dynamics of food webs in many ecosystems around the world. The skin is semi permeable, so it is easy to dehydrate, so they either live in wet places or have special adaptability to deal with dry habitats. Frogs make a variety of sounds, especially during the breeding season, and exhibit a variety of complex behaviors to attract mates, resist predators and generally survive.

Frogs are regarded as food by human beings, and have many cultural functions in literature, symbolism and religion. Since the 1950s, the number of frogs has greatly decreased. Since the 1980s, more than one third of the species have been considered endangered, and more than 120 species have been extinct. The number of deformities in frogs is increasing. A new fungal disease, Ampullaria, has spread all over the world. Conservation biologists are trying to understand the causes of these problems and solve them.