How They First Breathed

Early land animals didn't suck air into their chests the way we do. They gulped it, pumping their throat to force air down — the exact trick a modern frog still uses, its throat visibly fluttering.

Rib-driven breathing, where the chest expands to draw air in, came much later. It needed major changes to the skeleton and muscles before a body could pull air in instead of pushing it.