The spike shooting from a male Otton frog's pseudo-thumb. Credit: N. Iwai 
 
 A rare Japanese frog sports spikes protruding from a set of pseudo-thumbs, a scientist has discovered. The built-in weaponry helps the males grab onto females during sex and duel with competitors over mates, the researcher said. 
 
 Unlike most four-toed frogs, the endangered Otton frog (Babina subaspera) has a "fifth finger." In both males and females, this extra digit encases a sharp spine, but in males, this spike is more prominent, researcher Noriko Iwai from the University of Tokyo found. 
 
 Iwai believes the thumb-dagger evolved to allow males to anchor to the female during mating. And field observations in southern Japan's Amami islands, the frog's only home, showed that the males indeed jab their spikes into the sides of the females to hold on during amplexus — a form of pseudocopulation in which the males mount the female and fertilize her eggs as, or soon after, she lays them. 
 
 But it appears the frogs also use the spikes for male-to-male combat over females and breeding nests. The researcher found they wrestle with each other in an embrace while stabbing at each other with the spines. 
 
 "While the pseudo-thumb may have evolved for mating, it is clear that they're now used for combat," Iwai explained in a statement. "The males demonstrated a jabbing response with the thumb when they were picked up, and the many scars on the male spines provided evidence of fighting." 
 
 The Otton frog is native to southern Japan's Amami islands. Credit: N. Iwai 
 
 The spike, however, does not appear to cause lethal injuries during duels. Iwai noted a previous study of another frog with pseudo-thumb spikes, Hypsiboas rosenbergi, found that many males died after being stabbed in the eyes and ear drums by an opponent. Otton frogs don't appear to jab their rivals in these critical areas, and they have a raised patch on their sides that seems to guard against serious injury, according to the study. 
 
 "It seems that the intensity of combat in Otton frogs is finely balanced so as not to result in critical or mortal injuries, yet it remains aggressive enough to establish a clear victor," Iwai wrote in a paper published online today (Oct. 18) in the Journal of Zoology. 
 
 Follow LiveScience on Twitter @livescience. We're also on Facebook & Google+. ||||| Image copyright Jim McGuire Image caption The new species was discovered on Sulawesi Island in Indonesia; a male (L) and female (R) are pictured here 
 
 For the first time, frogs have been seen giving birth to tadpoles. 
 
 Most frogs lay eggs and although some species give birth to froglets, newborn tadpoles are new to science. 
 
 This species of fanged frog lives on Sulawesi Island in Indonesia, and zoologists had chased it for decades because they suspected it would show this unique behaviour. 
 
 An international team has now described it for the first time, in a study published in the journal Plos One. 
 
 Dr Jim McGuire from the University of California, Berkeley, actually thought he was holding a male frog the first time he witnessed a birth. 
 
 In fact, he had in his hands a pregnant female and, suddenly, a clutch of brand new tadpoles. 
 
 Mystery mechanism 
 
 Nearly all the world's 6,000 frog species use external fertilisation: the female lays eggs during mating, while the male releases sperm to fertilise them. 
 
 "But there are lots of weird modifications to this standard mode of mating," Dr McGuire said. 
 
 "This new frog is one of only 10 or 12 species that has evolved internal fertilization, and of those, it is the only one that gives birth to tadpoles, as opposed to froglets or laying fertilized eggs." 
 
 How the male frogs manage to fertilise eggs inside the female remains a mystery, because frogs have no conventional sexual organs to transfer the sperm. 
 
 Image copyright SPL Image caption Most frogs lay eggs, from which tadpoles eventually hatch 
 
 Two species found in California have evolved a penis-like "tail" that does the job, but the scientists found no such contrivance on the new Indonesian species. 
 
 Prof Djoko Iskandar, a collaborator of Dr McGuire's from the Bandung Institute of Technology in Indonesia, first spotted this new type of fanged frog in the 1990s but they had not been confirmed as a distinct species until now. 
 
 The scientists called the new species Limnonectes larvaepartus. The Limnonectes family are known as fanged frogs because of twin projections on their lower jaws that are used in fighting. 
 
 Race against time 
 
 Ben Tapley, team leader of herpetology at the Zoological Society of London (ZSL), said the new finding was "totally out of the blue". 
 
 "They're relatively dull frogs, actually," Mr Tapley told BBC News. "To find out something totally surprising about a frog you would barely notice in the forest is really cool." 
 
 There are thought to be up to 25 species of Limnonectes frogs on Sulawesi, but only four have been described so far - including the new larvaepartus. 
 
 Little is known about any of the animals' biology. 
 
 Image copyright Jim McGuire Image caption The newborn tadpoles are about 1.5cm long 
 
 "Finding a new species is not that rare - but actually discovering a new reproductive mode is," Mr Tapley said. 
 
 "There are more than 40 of these modes in amphibians, but this one is obviously totally unique." 
 
 He added that the region where the frog was discovered has one of the highest deforestation rates in the world. 
 
 "These kind of findings are really valuable, especially in Sulawesi where most of the forest is gone. 
 
 "It's great that we're learning about these species before it's too late." 
 
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– Meet the most badass frog in the pond: The Japanese Otton frog has what amounts to spiked thumbs, reports LiveScience. The scientist who made the discovery says the extra bony digit is used to help the male hang on during mating but also for fighting other males. It's apparently not a lethal weapon, because the boys seem to take care not to poke each other in the eye or ear drums. Discover has a great photo here—and it also uses the term "flick-knives" to describe the weaponry. "While the pseudo-thumb may have evolved for mating, it is clear that they're now used for combat," says the University of Tokyo scientist who made the find. "The males demonstrated a jabbing response with the thumb when they were picked up, and the many scars on the male spines provided evidence of fighting." A group of African frogs has retractable claws, but those frogs don't have the extra "psuedo-thumb." Advantage, Otton.