They're each smaller than a coin—and in big trouble.

Three salamander species recently identified from Oaxaca, Mexico, are likely headed for extinction, scientists say.

The newfound amphibians belong to what may be the most endangered genus of amphibians in the world: Thorius. Although once extremely abundant, all known Thorius species have declined precipitously over the last three decades, and living specimens are now difficult to find in the wild.

For that reason, nearly all the specimens examined in this study are museum specimens that are more than 35 years old. (See "Smallest Frogs Found—Each Tinier Than an M&M.")

Not only are the salamanders rare, they're so small that "many of their bones are extremely reduced and difficult to see,” says study