Fossil evidence suggests that the tiktaalik had lungs, which meant that it could breathe in air, instead of just water.
This trait allowed the tiktaalik to survive despite the low oxygen content of the shallow water because the tiktaalik would simply get its oxygen from the air. This selective advantage was passed on to the tiktaalik's offspring and over time, more amphibious creatures evolved with the ability to survive both on land and in water.
