London, October 2 : A new research has claimed that pterodactyls, ancient reptiles that could grow to the size of small aeroplanes, were too heavy to fly, even with their massive wings.
According to a report in the Telegraph, the problem, according to a leading scientist, is that they could not flap fast enough to create the thrust to keep their enormous bulk airborne.
The 'dinosaur' popularly known as a pterodactyl is actually called a reptile called a pterosaur, which is Greek for flying lizard.
It existed alongside the dinosaurs between 251 and 65 million years ago, and were thought to be the biggest creatures to ever take to the air.
But Katsufumi Sato, a Japanese scientist, who collected data from five large birds including the world's biggest, the wandering albatross, has calculated that it was physically impossible for them to stay aloft.
The University of Tokyo professor claims that the largest animal capable of soaring across the sky unaided could have weighed no more than 40kg (88lbs) or the size of a labrador dog.
Professor Soto, travelled to the Crozet Islands - halfway between Madagascar and Antarctica - and attached accelerometers, devices the size of AA batteries which measure thrust, to the wings of 28 birds from the five species including the albatross which is a soarer like the pterosaurs were thought to be.
Unlike turkeys or bustards, whose short wings are good for quick take-off but not for soaring, these larger birds fly long distances using dynamic soaring. They ride changing wind currents without moving their wings.
But when the wind dies down, or blows at a constant speed, they have to flap or be pulled down by air resistance and gravity.
The maximum speed a bird can flap is limited by its muscle strength and decreases for heavier species with longer wings.
Professor Sato said that animals heavier than 40 kg would not be able to flap fast enough to stay aloft. This would explain why the wandering albatross weighs only 22 kg (46lbs).
A bird weighing too close to 40kg would be incredible unstable and "would not have a safety margin to fly in bad weather", he added.
Palaeobiologists, who reconstruct the flight of pterosaurs, believe they were dynamic soarers with wingspans up to 15 metres across - enough to keep them airborne even if they weighed almost a quarter of a ton.
According to Dr Mike Habib, of Johns Hopkins Medical School in Maryland, a theory is that their wings were so large that, relatively speaking, wing load was low.
If a pterosaur spread its wings, staying on the ground would have been more of a problem than taking off.