AHC: Terrestial Cartilaginous Vertebrates

Is there any way a terrestrial (or semi-terrestrial, if you rather) animal could have evolved from Chondrichthyes concurrent with (or possibly instead of) bony fish? What kind of environment would they need to find on land to make this work? And what kind of animals could evolve from these forebears?
 
I'm not a biologist, but I think the softness of cartilage and the fact that chondrichthyes need to constantly move to not suffocate, is going to preclude their evolution onto land.
 
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