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The Otton frog (Babina subaspera), is a species of frog in the family Ranidae. It is endemic to the islands of Amami Ōshima and Kakeromajima in the Ryukyu Islands, Japan. Its natural habitats are subtropical or tropical moist lowland forests, freshwater marshes, and intermittent freshwater marshes. Once considered a delicacy as a source of food, it is now threatened by habitat loss through deforestation, and predation by introduced mongooses.

Otton frog
Scientific classification
B. subaspera
Binomial name
Babina subaspera
(Barbour, 1908)

Rana subaspera Barbour, 1908

It is one of only two species (the other being Babina holsti) to possess a "pseudothumb" on the forelimbs.[2]

Physiology and morphologyEdit

The Otton frog has been denoted the 'wolverine frog' due to hidden retractable claws, which are sharp and shoot out from under their thumbs. Both male and female Otton frogs have these claws, with male claws being typically longer than those of the females.

Like the five-fingered Hypsiboas rosenbergi frogs of Latin America, the Otton frog has five fingers.[3]


This rare frog uses its switch-blade claws to fight and in mating. Although both sexes have claws, apparently only the males use them, probably to anchor the female to the male during mating.[4]

During fighting, two male Otton frogs wrestle each other until in an embrace. They then impale their opponent on their retractable spikes.[4]


  1. ^ Yoshio Kaneko; Masafumi Matsui (2004). "Babina subaspera". The IUCN Red List of Threatened Species. 2004: e.T19172A8847183. doi:10.2305/IUCN.UK.2004.RLTS.T19172A8847183.en. Retrieved 27 December 2017.
  2. ^ Masayoshi Tokita & Noriko Iwai (2010). "Development of the pseudothumb in frogs". Biology Letters. 6 (4): 517–520. doi:10.1098/rsbl.2009.1038. PMC 2936208. PMID 20147308.
  3. ^ Briggs, Amy (2012-10-19). "The Deadly Thumbs of Japanese Flick Knife Frogs". National Geographic Society (blogs). Retrieved 2016-08-28.
  4. ^ a b Iwai, N. (2013-02-01). "Morphology, function and evolution of the pseudothumb in the Otton frog". Journal of Zoology. 289 (2): 127–133. doi:10.1111/j.1469-7998.2012.00971.x. ISSN 1469-7998.