Once tadpoles lose lungs, they never get them back https://phys.org/news/2025-10-tadpoles-lungs.html https://academic.oup.com/evolut/advance-article-abstract/doi/10.1093/evolut/qpaf192/8296690

"all #frogs have lungs, so #tadpoles retain the genetics to regain lungs when environmental pressures might favor having them but instead evolve alternate solutions... The lungless African red #toad lives in low oxygen waters, and while redeveloping lungs might seem like the obvious solution, these tadpoles have instead evolved a crest of vascularized skin on top of their heads"