Frogs make up about 88 percent of living amphibians
Frogs are tailless amphibians of order Anura—“without tail”—ranging from tropics to subarctic zones but richest in rainforest wetlands. They comprise roughly 88 percent of extant amphibians and rank among the five most diverse vertebrate orders. Wartier species get called toads, yet every anuran is a frog in cladistic speech.
Skin colours run from mottled brown, grey and green camouflage to vivid red or yellow warning patterns, and the glandular secretions range from merely unpleasant to toxic. The so-called tail of tailed frogs is actually an extension of the male cloaca. Anatomists define anurans by nine or fewer vertebrae before the hips, a urostyle of fused vertebrae, fused forearm and shin bones, elongated ankles and hind legs longer than the front. Tadpoles scrape food with specialised mouthparts suited to plant, mixed or plankton diets.
Over 7,700 species fill 59 families; the tree frogs of Hylidae lead with 1,062, ahead of Strabomantidae with 807, Microhylidae with 758 and true toads with 657. Some hybridise readily: the edible frog is a cross between the pool frog and the marsh frog, and fire-bellied toads form hybrid zones of less fertile offspring.
The oldest proto-frog, Triadobatrachus, comes from the Early Triassic of Madagascar. In 2008 the 290-million-year-old Gerobatrachus hottoni, found in Texas and combining frog and salamander traits, was hailed as a stem batrachian near their common ancestor, though a 2005 rDNA study had instead grouped salamanders with caecilians.
Old English used frosc for the animal, and frogga seems to be a nickname formed like dog, hog, pig and stag, while frosh and frosk lingered in dialects into the nineteenth century. Toad, from Old English tādige, gave Middle English taddepol, apparently toad-head. Frog numbers worldwide have fallen sharply since the 1950s, which makes them early warning signs of environmental damage.
Source: Frog
