Frogs are a diverse and largely carnivorous group of short-bodied, tailless amphibians
composing the order Anura. 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
found in tropical rainforests. There are approximately 4,800 recorded species, making
them among the most diverse vertebrate groups.
The body plan of an adult frog is generally characterized by a stout body, protruding
eyes, cleft tongue, limbs folded underneath and the absence of a tail. Besides living in
fresh water and on dry land, the adults of some species are adapted for living
underground or in trees. The skin of the frog is glandular, with secretions ranging from
distasteful to toxic. Warty species of frog tend to be called toads. Frog warts are
elevations in the skin where glandular toxins tend to concentrate. The distinction
between frogs and toads is based on informal naming conventions concentrating on the
warts rather than taxonomy or evolutionary history; some toads are more closely related
to frogs than other toads. Frogs' skins vary in colour from well-camouflaged dappled brown,
grey and green to vivid patterns of bright red or yellow and black to advertise
toxicity and warn off predators.
