How many times will lizards become "snakes"?

I love those, I also like deep-water wish with looong “legs” like that, they’re weird!
@benkendrick maybe, but I hope they would stay more agile and won’t grow ribcages like manatees, that’d be a minus for getting on land, though if they were still feeding on fish it’s unlikely, but who knows, what are the odds of them getting back to eating plants, did they loose all the symbionts they had for that or not? I know little about their digestion, other than that whales can swallow birds and poop them out whole.

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I just don’t see how mammals could re-evolve gills instead of lungs, the correct excretion system or swim bladders. It’s just not in mammalian DNA anymore. They might evolve into some other form of life that use water as a means of Oxygen exchange but they will never be fish. It’s far more likely that fish species would change to inhabit any niches left by mammals.

A paper written by a colleague of mine asked the question “ is a soft shell turtle a fish?” Softshells (Trionychidae) are able to absorb oxygen from water through tissues in their cloaca which supplements the O2 they acquire conventionally through surfacing and breathing. So perhaps fish-like in some respects but not fish.

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All of mammalian DNA wasn’t in mammalian DNA at one point. I see your point, and I’m not saying it’s likely for mammals to redevelop gills, just that given enough time it’s possible. It doesn’t matter if the pathway is probable, only that ‘fish’ is the evolutionarily preferred end state (or something like it as you say. I’m probably being a little more generous with the definition of ‘fish’ in my head) and that there is some way, however improbable, of getting to that state. Are we ever going to observe that state? Probably not. I’d bet on human extinction before that.