A frog's size is generally described by the length of its body, not including the legs. Biologists usually use the distance from the snout to the vent (SVL, snout-vent length). The legs are at least as long as the body, and generally much longer.
Two species tie for the smallest known living frog: one found in Brazil and the other in Cuba.
The Brazilian Gold Frog, or Izecksohn's Toad (Brachycephalidae didactylus1), is found in forests in the Brazilian state of Rio de Janeiro.
Photo courtesy, and © Martjan Lammertink.
Eleutherodactylus iberia. The coin is somewhere between 17 and 24 mm in diameter (can't see denomination).
The Cuban species, Eleutherodactylus iberia, was discovered2 in 1993 in leaf litter in the rain forest on the western slopes of Monte Iberia. The body of the adult is less than a centimeter long. Females lay a single egg at a time, which hatches into a miniature frog, avoiding the tadpole stage.
These two species are the smallest known tetrapods (four-legged animals, or those whose distant ancestors had four legs). The tetrapods include all the animals with backbones (vertebrates) with the exception of fish. Other leg-less vertebrates, like snakes and whales, do qualify as tetrapods; their embryos reveal that they had four-legged ancestors.
1. The frog was discovered by Izecksohn, who named it Psyllophyrne didactyla.
E. Izecksohn.
Novo genero e nova especie de Brachycephalidae do Estado do Rio de Janeiro,
Brasil (Amphibia, Anura).
Boletim do Museu Nacional, Rio de Janeiro. Nova série: Zoologia. No. 280, pages
1-12. (1971)
Subsequently the genus was recognized as one described much earlier:
M. Kaplan.
Histology of the anteroventral part of the breast-shoulder apparatus of Brachycephalus ephippium (Brachycephalidae) with comments on the validity of the genus
Psyllophryne (Brachycephalidae).
Amphibia-Reptilia, vol. 23, no. 2, pages 225-227 (2002).
2. A. R. Estrada and S. B. Hedges.
At the lower size limit in tetrapods: a new diminutive frog from Cuba (Leptodactylidae:
Eleutherodactylus).
Copeia, vol 1996, no. 4, pages 852-859 (27 December 1996).
The biggest living frog is the Goliath frog (Conraua goliath), found in Cameroon. Its body (not counting the legs!) is as long as 30 centimeters (a foot), and it weighs about 3.3 kilograms.
Illustration by Luci Betti-Nash. Courtesy David Krause, Stony Brook University
B. ampinga compared to a pencil and the largest living frog in Madagascar, which is about 4 inches long.
Perhaps the largest known extinct frog is Beelzebufo ampinga1, from fossils found in Madagascar. Comparing its bones to those of related living species led investigators to estimate its body length at more than 40 cm (16 inches).
1. Susan E. Evans, Marc E. H. Jones and David W. Krause.
A giant frog with South American affinities from the Late Cretaceous of
Madagascar.
PNAS, vol. 105, no. 8, pages 2951-2956 (26 February 2008).
www.pnas.org/cgi/doi/10.1073/pnas.0707599105
Harry Parsons.
The Nature of Frogs: Amphibians with Attitude.
New York: Sterling, 2000.
For young readers.
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Last revised: 25 March 2008.