The main difference between the frogs, many of which have fewer fingers and toes than most in order to optimize for their size, is skin color and texture. They produce varying levels of a neurotoxin called tetrodoxin, and their bright skin colors are a warning to potential predators.
To find the frogs, which live exclusively on their little mountain tops, researcher Marcio Pie of the Federal University of Parana and his colleagues had to trek up many small but rugged mountains, many of which lack well-marked trails. Since the area is so rich with members of the genus -- and since the mountains clearly separate one species from another -- it's pretty much assumed that each mountain searched for the first time will yield a new species. But frogs that grow less than a centimeter are pretty hard to spot.
"It takes a lot of practice and sometimes it's very frustrating, to go up the mountain for many hours and come back empty-handed," Pie told the BBC. "You can hear them singing and there's probably hundreds of them, but you simply can't catch them! Because once you get closer, just from the vibration in the ground, they keep silent for, say, 20 minutes or half an hour. And then you have to go through the leaf litter very carefully with your hands," he said.
Because their habitats are so exclusive, Pie and his colleagues warn that the frogs are in danger. Logging and climate change pose huge threats, especially because the frogs appear to be quite sensitive to temperature -- that's what keeps them on their mountain tops. To ensure the survival of the various species of the genus, the researchers say, we may need to start raising them in captivity -- and race to find the rest of them.