LOS ANGELES, CA (Catholic online) - Called the Otton frog, or Babina subaspera, these new species calls the Amami islands of Southern Japan its home. Both males and females of the species have the spike.

The study, conducted by Dr Noriko Iwai from the University of Tokyo found that unlike most other frogs, the Otton has an extra digit-like structure. It's a trait that the frog shares with the five-fingered Hypsiboas rosenbergi frogs of Latin America.

"Why these fifth fingers exist in some species remains an evolutionary mystery, but the extra digit of the Otton is in fact a pseudo-thumb," Iwai said.

"The digit encases a sharp spine which can project out of the skin, which fieldwork demonstrates is used for combat and mating," she said.

Studying the rare frogs since 2004, researchers wished to understand the species' distribution, breeding habits and range. These factors would be used in any conservation strategy.

Once Iwai began exploring how the Otton's use their pseudo-thumbs, she discovered that while both males and females had the spike, it was only used by males, who were found to have larger pseudo-thumbs than the females. Iwai believes that the spikes evolved for anchoring to the female, known as amplexus, the Latin for embrace, during mating.

"While the pseudo-thumb may have evolved for mating, it is clear that they're now used for combat," Iwai said.

"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," she said.

Spikes which shoot from fingers are a key weapon for Wolverine, the comic book superhero. Perhaps unfortunately, the image projected by the star of screen and comic books is slightly dented by the frogs' fighting style.

Rather than dueling with thumb spikes the males wrestle each other in an embrace, jabbing at each other with the spines.

This fighting style helps confirm the theory that the spines were original used for embracing mates.

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