Yes, that's the 'chicken or egg' view which is probably the main, definitive force but there are others, especially
the development of lungs. Amphibians at least in some stages of their life cycle can only "breathe
" in water - they have gills and/or can absorb oxygen through their skins. Developing an imporous (to oxygen) skin for all life stages necessitate the alternative (lungs).
I think there is a tendency, generally, in biology to infer that this
(or that) is the critical point, when, actually there were many.
Incidentally, I hope we're not misreading this ... is this about how amphibians evolved into reptiles or
how fish evolved into amphibians? Or both? Or something else?
Originally Posted by Engorons
A lineage of amphibian evolved a shelled-type egg known as the amnionic or cleidoic egg that could be laid on land and become the first reptiles.
I suggest you check out the "tuataras" on the internet.