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.
As of early 2012, the smallest known frog was Paedophryne amanuensis, with an average SVL of 7.7 mm¹. Its genus, Paedophryne, had been defined only two years earlier by a biologist² who had discovered, also in New Guinea, the previous record holder, Paedophryne verrucosa. That species's females averaged 9 mm and the males a half millimeter smaller.
Before the finds in New Guinea, the record for smallest known living frog was a tie between one found in Brazil and another in Cuba.
The Brazilian Gold Frog, or Izecksohn's Toad (Brachycephalidae didactylus3), is found in forests in the Brazilian state of Rio de Janeiro.
Photo courtesy, and © Martjan Lammertink.
The Cuban species, Eleutherodactylus iberia, was discovered4 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.
All these species, though geographically distinct, are found in tropical wet-forest leaf litter. These are not aquatic frogs, and most do not have a tadpole stage. To appreciate some problems of being a small frog, contemplate the surface-volume relationship. and see reference one for a discussion.
These microfrogs 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. Eric N. Rittmeyer, Allen Allison, Micael C. Gründler, Derrick K. Thompson, Christopher C. Austin.
Ecological Guild Evolution and the Discovery of the World's Smallest Vertebrate.
PLoS ONE 7(1): e29797.(2012)
2. F. Kraus.
At the lower size limit for tetrapods, two new species of the miniaturized frog genus Paedophyrne (Anura, Microhylidae).
ZooKeys 154, pages 71-88. (2011).
New genus of diminutive microhylid frogs from Papua New Guinea.
Zookeys 48, pages 39-59 (2010).
Luiz F. Ribeiro, Marcos R. Bornschein, Ricardo Belmonte-Lopes, Carina R. Firkowski, Sergio A. A. Morato and Marcio R. Pie.
Seven new microendemic species of Brachycephalus (Anura: Brachycephalidae) from southern Brazil.
PeerJ, 4 June 2015.
3. The frog was discovered by Izecksohn, who named it Psyllophyrne didactyla.
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:
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).
4. 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
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).
The Nature of Frogs: Amphibians with Attitude.
New York: Sterling, 2000.
For young readers.
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Last revised: 16 June 2015.