Air-powered flight
11 May 2009, by Sara Coelho
How do birds fly? It helps to have wings, but they are nothing without an efficient breathing mechanism built with special lungs and air-sacs for added power.
Dimorphodon macronyx, a pterosaur from the Early Jurassic. Image: Mark Witton, University of Portsmouth.
Now scientists discovered that ancient flying reptiles evolved the same features earlier than previously thought.
Pterosaurs first appeared about 230 million years ago, in the Late Triassic, and rapidly became masters of the skies at the time of the dinosaurs. Some of the later species were the largest flying animals of all time with a wingspan of up to 12 metres. They were able to grow large and still fly thanks to air-sacs connected to the lungs to keep blood oxygen levels high, and hollow air-filed bones to make them lighter.
Today these adaptations for flight are seen only in birds. Dr Richard Butler and his colleagues at the Natural History Museum set up a project to find out how reptiles evolved air-sacs and hollowed bones. The mainstream idea was that 'early pterosaurs did not have hollow, or pneumatised, bones and thus could have lacked air sacs', says Butler. 'It was thought possible that these features evolved independently in birds and pterosaurs.'
The team analysed fossils from two pterosaur species from the Triassic and one from the earliest Jurassic. They were looking for little openings called foramina, evidences of hollow bones connected to the air-sacs. 'We could identify and measure the openings in the sides of the fossil vertebrae,' explains Butler.
They found that the openings in these species had the same size and elliptical shape as the foramina recorded in late pterosaur fossils and modern birds. This means that they shared the same function and that early pterosaurs had a complex breathing system, well adapted to the demands of flight.
The findings, published in Biology Letters, have wider implications for the origins of flight and respiratory systems. 'It now seems likely that air-sacs and hollowed bones evolved much earlier than we thought,' says Butler.
The first animal to develop this specialised breathing system was probably an ancient reptile that lived before the line of pterosaurs was separated from the dinosaur and bird branch.
Richard J. Butler, Paul M. Barrett and David J. Gower. 2009. Postcranial skeletal pneumaticity and air-sacs in the earliest pterosaurs Biol. Lett. doi:10.1098/rsbl.2009.0139
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