What the Move Cost

Quick recap of the rebuild that getting ashore required:

• Lungs — already present in early air-gulping fish — became the full-time way to breathe.
• Fins became limbs strong enough to push against gravity.
• In mammals, jaw bones became ear bones to catch sound in air.
• A spine learned to hold weight, not just bend for swimming.

None of this was planned. Each change was a workaround that happened to keep an air-gulping fish alive.