Lizard Has One-Way Breathing; Hints at How Dinosaurs Breathed?

That’s surprising, because the unidirectional airflow of birds was thought to have evolved due to the high-oxygen demands of flight: Instead of being partially filled with stale, depleted air like human lungs, avian lungs contain air with a much higher average oxygen content and are much more efficient at getting oxygen to the blood.

So this method of breathing was generally considered to be unique to both warm-blooded animals and birds.

Source: Here