Pterosaurs were the first vertebrates to evolve true flapping kind of flight, a complex and physiologically more demanding activity .Researchers always suspected that these extinct reptiles sustained flight through flapping, based on fossil evidence from the wings, but there was little understanding on how the energy demands for the activity were met. A new study published February 17 in the journal PLoS One by researchers from Ohio University, College of the Holy Cross and the University of Leicester explains how balloon-like air sacs, which extended from the lungs to inside the skeleton of pterosaurs, provided an efficient breathing system for the ancient beasts. Using X-ray movies and CT scans , authors were able to reconstruct the breathing system in pterosaurs, which shares many similarities with modern birds.
Because fossils rarely preserve soft tissues, the research team conducted a comparative study that included pterosaurs, birds and crocodilians in order to get a better understanding of the relationships among air sacs, lung structure and the skeleton. the group characterized how the skeleton works to move air through the lungs in living animals, and also how to identify the signature traces left on bones that have been invaded by air sacs.

Not only do the extinct pterosaurs show evidence that their bones that were invaded by air sacs, but patterns of pneumaticity throughout the entire skeleton of different pterosaur species parallel trends identified in many living bird groups.

In this authors present various lines of skeletal evidence that indicate that pterosaurs had a highly effective flow-through respiratory system, capable of sustaining powered flight, predating the appearance of an analogous breathing system in birds by approximately seventy million years. Convergent evolution of gigantism in several Cretaceous pterosaur lineages was made possible through body density reduction by expansion of the pulmonary air sac system throughout the trunk and the distal limb girdle skeleton, highlighting the importance of respiratory adaptations in pterosaur evolution, and the dramatic effect of the release of physical constraints on morphological diversification and evolutionary radiation.

Reference and image credit:
Claessens LPAM, O’Connor PM, Unwin DM (2009) Respiratory Evolution Facilitated the Origin of Pterosaur Flight and Aerial Gigantism.
PLoS ONE 4(2): e4497. doi:10.1371/journal.pone.0004497

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