The rare Otton frog is being likened to the fictional character Woverine since it comes equipped with spikes that can shoot out of its "thumbs." These digits cannot actually
function as thumbs, but contain retracted little blades. Both males and
females have the blades, but only males make use of them.
Scientists say that the males use these blades in combat and to hold on to females during mating. Unlike most frogs (see photo) which have four digits on each hand, the Otton has what appears to be a fifth digit in which the blades are kept, something like a cat's retracted claws. Researchers believe that the spikes most likely evolved for mating, but ended up also being handy in a neighborhood rumble with all comers.
The Otton is native to islands in southern Japan in tropical and subtropical rainforests. The spike helps them wrestle for nesting areas and mates. The ability to retract the blade helps ensure that the frogs don't injure themselves.