Frogs and toads (collectively referred to as anurans, although this is not a common word) are a large order ( Order Anura, about 3,500 species) of animals belonging to the amphibian class (Class Amphibia). Their closest living relatives are the newts and salamanders (Order Caudata, aka Urodela), plus an obscure order of amphibians, the caecilians (Order Gymnopoda). Together, these three orders form the Class Amphibia. Modern amphibians are much smaller than their prehistoric relatives, to whom the anurans bear little external resemblance today.
Anurans have conquered all parts of the world except for Antarctica and the North Pole. They are particularly abundant in the topics, especially Asia, but equally are found in the cooler parts of Europe as well as the deserts of Australia and Africa.
Amphibians belong to the vertebrates, or back-boned animals, a group that also comprises the fish, reptiles, birds and mammals. Compared with the other 95% of the animal kingdom, vertebrates share a vast number of common characteristics. In particular, most people tend to mentally lump amphibians and reptiles together. However, there are also important differences between amphibians, reptiles and mammals, which if overlooked can make a captive amphibian's life a miserable one.
Frogs and toads can normally be characterised by a moist, porous skin (in common with all other amphibians) and, more specifically, two ordinary front limbs and two rather more developed rear limbs, in contrast to newts and salamanders, which have limbs of roughly equal length, and caecilians, which have none at all. No frogs or toads have tails, whereas newts and salamanders do. Other than this the various anuran species have a variety of environments, lifestyles and, unusually for herptiles (reptiles and amphibians) a variety of mating calls that vary as much between species as the songs of different birds. The vast majority return to water to breed, or at least to give birth, but again there is also a fascinating diversity of reproductive habits.
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