Amphibian-Skinned Monsters in Volcano?

Isn't it weird how amphibian-like monsters who usually live in swamp-lands or jungles are also commonly found in the Volcano? Like Ioprey, Iodrome, Furogi, Dosufurogi, and Zuwaroposu. Is it because of that old myth that salamanders are resistant to fire, or the monsters' skin is very thick, or that the skin it contains moisture, or what.....? Because amphibian skin constantly needs moisture, and dry out quickly.