Deep breath in, deep breath out
We breathe in and out along the same pathway, which mixes fresh and stale air in the lungs, so only part of the fresh oxygen breathed in can be used. Like birds, pterosaurs had a much more efficient, one-way flow-through breathing system, in which fresh air and stale air never mix.
Animals that have this breathing system gain more energy from each breath, important for active animals that need to minimize weight and maximize energy usage for flight. Also like birds, pterosaurs had many air sacs spread throughout the body. They even had air sacs in their bones, which would have made them more lightweight without compromising strength.
The energetic lifestyle of pterosaurs was enabled by an efficient breathing system similar to modern birds.
The respiratory system of pterosaurs was like that in modern birds, with a one-way lung and a system of air sacs. Pterosaurs did not use a diaphragm to inflate the lungs like mammals. Instead, they used abdominal muscles to move the ribs and sternum, squeezing the air sacs, like in birds.
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Posterior air-sacs
When pterosaurs inhaled, fresh air went first into posterior air sacs instead of going directly into the lungs. This air sac worked as a staging area for the fresh air before moving on.
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Lungs
From there, it moved to the lungs, going from back to front without mixing fresh and stale air. Like all air-breathing vertebrates, gas exchange (the trading of carbon dioxide for oxygen) only happens in the lungs.
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Anterior air-sacs
After crossing the lungs, the stale air moved into the anterior air sacs before being exhaled. This allowed the lungs to continually be fed fresh air without being mixed with stale air.
