A flying reptile that lived 100 million years ago and had an 18m wingspan has entered the record books as the largest-known animal to have taken to the air. Scientists discovered the fossilised bones of the dinosaur-like creature at a site in Mexico and have calculated that its wingspan was nearly twice the length of a Spitfire's.

Details of the pterosaur, the first animals with backbones to fly, emerged at the British Association's Science Festival in Dublin. It was described by Dr David Martill of Portsmouth University from work carried out by Dino Frey of the German Staatlichen Museum fur Naturkunde in Karlsruhe.

Only fragments of wing bones have been discovered but their size and dimensions indicate that the animal must have had a wingspan of at least 18m.

The largest flying bird today is the wandering albatross, with a wingspan of about 3.5m, which means that some pterosaurs were more than five times the size.

"A Spitfire has a wingspan of 11m and has to be powered by a Rolls-Royce Merlin engine," Martill said. "Pterosaurs did it on a diet of fish and a superb ability to utilise air currents, thermals and ground effects.

"There is nothing close to pterosaurs alive today. Pterosaurs went extinct 65 million years ago, they left no descendants and we don't know quite what their closest relative was.

"We believe they were mostly fish feeders, but there are some wide-mouthed forms that probably ate insects and there were some with comb-like teeth and they were probably filter feeders, a little bit like flamingos."

Pterosaurs could walk on four legs using the "knuckles" of their hands. They flew with the help of an ultra-thin membrane just half a millimetre thick, which was stretched between its neck, tail and wings.

"Exceptional tissue preservation shows that this membrane was a very sophisticated structure. It wasn't just a piece of skin."

Although it was originally thought pterosaurs merely glided, it is now believed they flapped their wings for powered flight. "If they were able to use a frog-like jump, that would have given them an extra bit of lift," Martill said. "We call them dynamic soarers but it seems like they all had the musculature to flap. It is powered flight."

Embryonic pterosaurs recovered from fossilised eggs indicate that they could fly soon after they hatched, unlike modern birds which have to grow to nearly full-sized before they can safely leave the nest.

It is possible that the giant flying reptiles used a phenomenon called winging ground effect, when a flying object experiences extra lift when skimming the surface of the sea or flat piece of ground.