For almost a century, scientists struggled to explain how the extinct reptiles called pterosaurs managed to get off the ground. In regard to the smaller pterosaurs, bird models sufficed; flapping from standstill or a running start could work. But for the larger pterosaurs, some of which had a 26-foot wingspan and weighed 200 pounds, scientists could not find a bird model that explained takeoff.
That is because they did not take off like birds, thinks Michael Habib, who studies functional anatomy and evolution at Johns Hopkins University. After analyzing the biomechanics of the creatures, Habib proposes that pterosaurs took flight by using all four limbs to make a standing jump into the sky, not by running on their two hind limbs or jumping off a height, as more widely assumed.
“I started as a bird researcher,” Habib says. “I became interested in mechanical limits in flying animals, and that naturally leads to pterosaurs.”
And pterosaurs such as Quetzalcoatlus sit firmly on the far end of those limits. Even with its birdlike hollow bones, Quetzalcoatlus weighed between 250 and 550 pounds and had about a 36-foot wingspan. By comparison, an albatross weighs about 18 pounds and has an 11-foot wingspan. It had to take off somehow, but no one had a good guess how.
By analyzing the shape of the pterosaur arm bones, Habib calculated that the forelimbs could withstand stresses far greater than those encountered during flight. But why evolve reinforced wings if they would never experience high stress? Habib then made the connection between the quadrupedal gait of the large pterosaurs and the jumping quadrupedal takeoff he had seen in vampire bats. If the large pterosaurs used all four limbs to get off the ground, that would explain both the superstrong forelimbs and solve the mystery of pterosaur takeoff.
But just because an animal could do something does not mean it did, and some paleontologists remain unconvinced that Habib’s data actually explain how pterosaurs got off the ground. “When I read the manuscript, my first reaction was, ‘Hmm, that’s odd.’ But if you work on pterosaurs, you get used to odd things anyway,” remarks David Unwin, a paleontologist at the University of Leicester in England and author of the book The Pterosaurs: From Deep Time. “Large and giant pterosaurs pose a problem,” he explains, “because the flying speed they need to achieve is quite high, 30 or 40 miles per hour, and I have a hard time understanding how they get that fast from a standing jump.”
Paleontologist Kevin Padian of the University of California, Berkeley, also questions some of Habib’s conclusions. Padian says he believes the smaller pterosaurs (some were the size of sparrows) were bipedal and thus took off with two legs, not four. He also does not think Habib has covered every kind of relevant bone stress.
The divide between the pterosaur researcher and the researcher looking at pterosaurs is fairly common in this area of paleontology. According to both Unwin and Habib, pterosaurs, with their improbable size and ability to fly, draw in biomechanics experts more focused on physics than prehistoric biology. “Because of the bizarre nature of pterosaurs, they’ve attracted attention from outside paleontology,” Unwin says. “So we’ve had a disproportionate number of people come in from outside paleontology, lots of people ready to have a go at the aerodynamics who are not pterosaur researchers first.”
Still, all agree that Habib brings up interesting points, and they are not just for biomechanics. Showing that the large pterosaurs could take off without having to jump off a cliff expands the range of places they could have lived, raising all kinds of questions about the ecology of large pterosaurs. Says Padian: “Every time we think we’ve figured them out, they throw us another curve.”
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Add CommentAs a former windsurfer I can tell you that it doesn't take much oomf to get the sail up as long as you angle it correctly into the wind. Perhaps it is as simple as settling in a windy area and using the leaping technique along with correct positioning of the wings into the wind!
Reply | Report Abuse | Link to thisI remember having read about the former existence of a cliff hundreds of miles long from where those things may have started flying just jumping into the ascendent air column that originates when a wind hits a slope. There is a modality of sailplane flying that uses the same principle, once upon a time, an spanish sailplane pilot (Ara or Juez?) hold a world record of sailplane endurance by flying in slope wind. Salut +
Reply | Report Abuse | Link to thisWas the atmosphere denser then? Was there stronger prevailing wind flowing to certain direction all the time? Were there plenty of fish very close to or above water surface to be scooped up while they were flying? Otherwise once those creatures landed on somewhere to feed, then they might have not been able to fly again to escape from their predators. Or were they eating flying insects? Very interesting and fascinating beings. Puzzles me all the time.
Reply | Report Abuse | Link to thisThe windsurfer dude/dudette brings up an interesting possibility. But, if the pterosaur is on land when there is no wind, the problem of protecting itself from predators remain. Perhaps the especially beefy forelimbs were actually used as clubs, and not necessarily for superman-style leaps. A muscular clubbing of said predator might be enough to allow the pterosaur to dissuade it from using it as its next meal.
Reply | Report Abuse | Link to thisCreatures weighing more than 200 pounds with 34 foot wingspans can frequently be seen flying from hills and dunes as small as 10 feet high near where I live. With a headwind of 10-12 miles an hour they only require two or three short steps to get airborne and can easily get airborne with a brisk run of 6-8 steps from any moderate sized hill in no wind at all. Many of them are capable of remaining aloft with airspeeds as low 17 mph rather than the 30 to 40 noted in the article. These creatures are of course hang glider pilots.
Reply | Report Abuse | Link to thisNearly all experienced hang glider pilots have experienced "bullet thermals." These are narrow, sharp columns of rising air that are not more than a few feet in diameter and create momentary changes in velocity of 1000 ft/minute or more in under a second. If the researchers calculated the airborne stress on the front limbs based solely upon the stress that the wing experiences in calm air, they missed the substantial impulse forces resulting from these thermals. The leading edges of modern hang gliders consist of stout aluminum tubing in part so that they can withstand these forces.
With the exception of the seemingly useless narrow pointed tips a modern hang glider looks remarkably like the pterosaur's wings. If you are seriously interested in understanding how the air behaves in their environment a visit to a club site and a willingness to ask questions could be very enlightening. The National Association is the USHGPA, easily found by googling.
"Creatures weighing more than 200 pounds with 34 foot wingspans can frequently be seen flying from hills and dunes as small as 10 feet high near where I live. With a headwind of 10-12 miles an hour they only require two or three short steps to get airborne and can easily get airborne with a brisk run of 6-8 steps from any moderate sized hill in no wind at all. Many of them are capable of remaining aloft with airspeeds as low 17 mph rather than the 30 to 40 noted in the article. These creatures are of course hang glider pilots. "
Reply | Report Abuse | Link to thisAnd do these hang glider pilots land back at the same spot they took off at in all kinds of weather conditions? Do these hang glider pilots have the ability to take off at will from any location to avoid predators? Do these hang glider pilots need to attach 30hp+ motors to their back to achieve powered flight?
InBoulder, My point was that it isn't difficult for a 250 pound creature with a 35 foot wingspan to achieve flight without the benefit of a high cliff. We do it all the time, and yes we are quite capable of landing at the same spot where we took off after having flown for hours without any source of power whatsoever other than the thermals and the wind.
Reply | Report Abuse | Link to thisIf humans can do this without a great deal of strength and the aid of a prosthesis, I suspect that the pterosaurs might have been able to do it as well. If the pterosaurs landed on a flat area near a hill, a short climb might be all it needed to get airborne once again.
Dan T, your points about hang gliders are interesting, although I must say that I have I found some major things were different between hang gliders and pterosaurs, especially large members of pterodactyloidea. For example, most members of pterodactyloidea are characterised by long necks, made up of fairly long cervical vertebrae. This can especially be seen in azhdarchids like arambourgiania and quetzalcoatlus. Thus, the head and neck, although lightly built, do provide some imbalance when comparing to the relatively puny hind limbs of these pterosaurs. A running start does not seem feasible to me at all. I have read in Peter Wellnhofer's book The Illustrated Encyclopedia of Pterosaurs that relatively litte wind speed would be needed to get these animals airborne, seeing as their wings covered such a large surface area. However, the pterosaurs must be at a complete standstill. They have a very little chance of staying upright for very long due to the massive imbalances caused by the long neck and head against the small limbs.
Reply | Report Abuse | Link to thisCould it be that they pulled their necks in for take-off, and extended them for searching and for flight control later?
Reply | Report Abuse | Link to thisAs Dan T says, climbing back up could help them take off from low heights, land lower and do it all again. So, could the strong fore-limbs be for climbing back up?