What physical constraint limits the size and environmental tolerance of lungless salamander species?

Answer

The reliance on gas exchange solely across the skin surface

Lungless species depend entirely on diffusion across their thin, moist skin for all gas exchange, which imposes a hard limit on how large they can grow and how dry their environment can be.

What physical constraint limits the size and environmental tolerance of lungless salamander species?
biologyamphibiancharacteristicSalamander