Air-filled bones helped prehistoric reptiles take first flight

Feb 18, 2009
Image copyright Mark Witton, 2009

(PhysOrg.com) -- In the Mesozoic Era, 70 million years before birds first conquered the skies, pterosaurs dominated the air with sparrow- to Cessna-sized wingspans. Researchers suspected that these extinct reptiles sustained flight through flapping, based on fossil evidence from the wings, but had little understanding of how pterosaurs met the energetic demands of active flight.

A new study published today 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. The system reduced the density of the body in pterosaurs, which in turn allowed for the evolution of the largest flying vertebrates.

"We offer a reconstruction of the breathing system in pterosaurs, one that proposes the existence of a mechanism with the same essential structure to that of modern birds — except 70 million years earlier," said study co-author Leon Claessens, an assistant professor of biology at the College of the Holy Cross.

Courtesy of Claessens, O'Connor, Unwin, 2009

The system would have facilitated the necessary gas exchange to enable sustained activity, added co-author Patrick O'Connor, an assistant professor of biomedical sciences at the Ohio University College of Osteopathic Medicine.

Claessens and O'Connor were inspired to conduct the study after David Unwin of the University of Leicester, then curator at the Natural History Museum in Berlin, showed them an extraordinarily preserved pterosaur in 2003. The scientists thought the specimen might finally shed light on how the animals powered sustained flight.

"The shape and size of the rib segments that articulate with the sternum indicate that the ribcage was mobile, contrary to previous ideas," Claessens said.

Unique and previously unrecognized projections on the ribs provided important leverage for the muscles that power lung ventilation, he added.

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. By using X-ray movies and CT scans, 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. For example, there is a direct relationship between the proportion of the skeleton invaded by air sacs and the absolute body size of an animal.

"Whereas small-bodied pterosaurs and birds typically pneumatize only a restricted part of the backbone, larger-bodied species routinely pneumatize most bones of the body, including the wing skeleton out to the ends of the fingers," O'Connor said.

Such modifications of the skeleton would have reduced bone density and resolved a major problem with sustaining flight in large-bodied pterosaurs: the energetic cost of keeping a heavy body up in the air. Density reduction of the skeleton in pterosaurs may have been beneficial, particularly so in the aerial giants—just as it appears to be in the largest flying birds today.

Air sacs in birds also serve other purposes, such as for visual displays and the production of sound, the researchers said. The existence of an analogous air-sac system in pterosaurs highlights new areas of research in which paleobiologists can explore aspects of pterosaurian biology.

Provided by Ohio University

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QubitTamer
4.5 / 5 (2) Feb 18, 2009
I once had a conversation with someone who was a skeptic of the theory of evolution. She was not a creationist by any means so her doubts were based on credible science based reasoning. One of the major questions she had was how did flying dinosaurs and then birds come about? Exactly what were the circumstances which completely changed the engineering of a creature from terrestrial to airborne. Where are the fossils of the in-between species? I have never been able to bring solid or substantive science to bear against this question and it bothers me immensely that these flying dinosaurs just appear in the fossil record and that this question remains unanswered.
Birger
not rated yet Feb 18, 2009
Useful adaptations will spread rapidly through the gene pool of any species, making the new variant or new species appear very quickly by a geological timescale. Often, no fossils of a transitional form survive. A possible explanation for the development is that a transitional form used gliding, like some squirrels and even snakes do today. If mutations of muscle attachments allowed muscles to give a useful boost to the range, the development of animals with increasing glide range might be relatively straightforward. (PS Pterodactyls are not dinosaurs, but another group of reptiles, thus showing the evolutionary flexibility of early reptiles)
Mercury_01
4.2 / 5 (5) Feb 18, 2009
I bet the bones were filled with hydrogen, and when the pterosaurs crashed, there were phenomenal explosions. Plus they had lasers.
Sophos
3 / 5 (2) Feb 18, 2009
I'm with Qubit on this. It seems that an adaptation which make air travel more efficient would limit survival on the ground or trees. An adaptation that grew bigger flaps (or muscles) on flying squirrels would limit their ability to escape predators in the trees?
QubitTamer
not rated yet Feb 18, 2009
I think it was yeah... probably lasers.
Tesla444
1 / 5 (2) Feb 19, 2009
Further to QubitTamer's & Birger's comments: Concerns about the lack of 'transitional' species are valid and can't be so easily explained away as Birger implies. The whole idea of evolution is that it happens over millions of years, yet Birger would have us believe that it happens in only years. The facts are that there are 'no' transitional species that have yet been found, barring a few scattered claims of some. If species do evolve from one to another (the basis of evolution) shouldn't there be millions (or at least 100's) of fossils of such transitional 'trial & error' examples as each species evolved to its next level - curiously, we only see the final version with none of the 'errors'. Maybe it is time to just accept that the facts prove this to be in error and we should modify this 'belief' to fit the scientific facts. I thought 'belief' was only part of religion. Why does it seem to play such a big role in Evolutionary Science. If you really believe in scientific method this deserves serious consideration.

Also, the fossil record seems to show that virtually all species simply appear in one time frame, exist in various forms for multiple Centuries, then disappear. This would seem to offer scientific facts that demonstrate that no Species ever evolves into a new unrelated Species. Given this perhaps we need to re-think Evolution.

Food for Thought!

FYI - I am non-religious and very much science oriented.

tesla444

Further to QubitTamer's & Birger's comments: Concerns about the lack of 'transitional' species are valid and can't be so easily explained away as Birger implies. The whole idea of evolution is that it happens over millions of years, yet Birger would have us believe that it happens in only years. The facts are that there are 'no' transitional species that have yet been found, barring a few scattered claims of some. If species do evolve from one to another (the basis of evolution) shouldn't there be millions (or at least 100's) of fossils of such transitional 'trial & error' examples as each species evolved to its next level - curiously, we only see the final version with none of 'errors'. Maybe it is time to just accept that the facts prove this to be in error and we should modify this 'belief' to fit the scientific facts. I thought 'belief' was only part of religion. Why does it play such a big role in Evolutionary Science. If you really believe in scientific method this deserves serious consideration.

Also, the fossil record seems to show that virtually all species simply appear in one time frame, exist in various forms for multiple Centuries, then disappear. This would seem to offer scientific facts that demonstrate that no Species ever evolves into a new unrelated Species. Given this perhaps we need to re-think Evolution.

Food for Thought!

FYI - I am non-religious and very much science oriented.

Thanks!
Sonhouse
not rated yet Feb 21, 2009
What we see today in the fossil record is there because of the large #'s of the species in question. It's a matter of statistics, if you have 10,000,000 of a species alive and then they die, chances are pretty good we will find one fossilized 100 million years later. But the transitional variety would not have existed for very long by definition, it is transitional, so instead of ten million as in my hypothetical example, there may only be 1,000 so the chances of finding one fossilized 100 million years later is a thousand times more difficult and that has been the case for the last 200 years of evolutionary theory. Don't expect someone to find a clear transitional birdlike fossil any time soon, it's the old needle in a haystack thing. Does not require supernatural intervention.
smiffy
not rated yet Feb 22, 2009
But the transitional variety would not have existed for very long by definition, it is transitional
By inventing the term 'transitional' you do not explain the mystery. You 'explain away' the mystery.
Ethelred
1 / 5 (1) Feb 23, 2009
The whole idea of evolution is that it happens over millions of years, yet Birger would have us believe that it happens in only years.


He said no such thing as years. Just not millions of them. Thousands for example is a fairly long time. Such distortions are popular with creationist of all kinds.

The facts are that there are 'no' transitional species that have yet been found, barring a few scattered claims of some.


False. ALL fossils are of transitional species in the first place. If you are fossilized your remains will be a transitional fossil. Many species have very detailed fossil records with the horse being the most well know set of transitional fossils. We have many transitional fossils of whales and their ancestors and of us for that matter. Lucy is so transitional that one creationist called her an ape and another called her a human (creationists are barred by ideology from admitting to transitional fossils so they lie a lot).

species do evolve from one to another (the basis of evolution) shouldn't there be millions (or at least 100's) of fossils of such transitional 'trial & error' examples as each species evolved to its next level


There are at least hundreds. Several in the human line that we know of. Its why its hard to tell with some Australopithecus fossils whether they are hominid ancestors or not since they are transitional into either hominids or some other species of Australopithecus(plus scientist feel there is prestige in finding a new species so they tend to claim more then they find).

curiously, we only see the final version with none of 'errors'.


Another misunderstanding of evolution. There are no errors in species. Just dead offspring that fail reproduce. There are no 'final' versions either. All species are evolving, its just that its hard to see over short time periods and in some species they fit their environment so well the rate of change is unobservable until there is a large change in the environment. At which point they must change rapidly or go extinct. Extinction without producing different species is what is what has happened in most species.

Also, the fossil record seems to show that virtually all species simply appear in one time frame, exist in various forms for multiple Centuries, then disappear.


Various forms equals evolution. But it is true that MOST species fail to adapt enough at eventually. Most in no way equals all. Its multiple megayears by the way not centuries. You seem to have a difficulty the time issue something not uncommon amongst Young Earth Creationists.


FYI - I am non-religious and very much science oriented.


Then try learning some actual science and quit getting bogus information from AnswersinGenesis.com.

I recommend:

The Blind Watchmaker - Richard Dawkins

Climbing Mt. Improbable - Richard Dawkins

Shadows of Forgotten Ancestors - Carl Sagan and Anne Druyan.

Wonderfull Life - Steven J. Gould

http://www.talkorigins.org/

Origin of Species - Charles Darwin but only if you really feel the need as its a bit archaic and dry. I haven't finished it myself.

The Dover Trial apparently had a lot of transitional forms brought up.

Yes I do understand that I said all life is transitional. I just want to make it clear that there are no end points except extinction. There are periods of rapid change which produce variants that are most least awkwardly discussed as transitional forms. If it walks like a duck and quacks like a duck its easier to call it a duck instead of awkward phrases like almost a duck or a post-duck birdlike entity.

Ethelred
Ethelred
not rated yet Feb 24, 2009
Sophos, keep that up and I will hunt down all your posts. There was no excuse for giving my post a one. Tit for tat. Your post was crap and I still didn't give it one till you did that to me. Do it again and you know now now what the results will be.

Ethelred
And I am ready.