A fossilised section of beak found in the UK is from the world\'s largest toothed pterosaur, say scientists. The fossil, dated to 100 million years ago, was kept at London\'s Natural history Museum but had not been thoroughly studied. Using the fragment to reconstruct the extinct beast, experts estimated that its wingspan measured up to 7m. They say it is the \"first substantial evidence for such large pterosaurs in the Early Cretaceous Period\". David Martill from the University of Portsmouth and David Unwin from the University of Leicester reported the discovery in the journal Cretaceous Research.Known as pterodactyls to many, winged reptiles from the order Pterosauria first appear in the fossil record 215 million years ago. \"Early pterosaurs were relatively small, with wing-spans not much bigger than a crow,\" explained Dr Martill \"These early pterosaurs all had a mouth full of teeth, usually small at the back and larger at the front.\" However, fossil finds have shown that in the late Jurassic Period pterosaurs diversified greatly, with two groups losing their teeth and becoming land-based giants. For example, the remains of the huge, toothless Hatzegopteryx - discovered in Transylvania - indicated an animal with a wingspan of 12m. But until this discovery, toothed species were thought to have been much smaller, with a maximum wingspan of 5m. This unusual fossil fragment was uncovered during the 19th Century, while workers were digging for phosphate fertiliser near Cambridge, in an area known as the Cambridge Greensand. Some of the layers of rock here date back to the Early Cretaceous.It was given to the Natural History Museum by renowned fossil hunter Sir Richard Owen who helped found the museum and famously coined the word \"dinosaur\". However, beyond being labelled \"pterosaur\", the fossil had not been formally described. \"It\'s an ugly looking specimen... but with a bit of skill you can work out just exactly what these bits and pieces were,\" explained Dr Martill. \"We have the tip of the upper jaws - bones called the premaxillae. There are some tooth sockets and fortunately a single tooth is preserved in one socket. \"Although the crown has broken off the tooth, the diameter is 13mm. This is huge for a pterosaur. \"Once you do the calculations you realise that the scrap in your hand is a very exciting discovery.\" Using the tooth measurement, and by studying the proportions of co-existing species from the Cretaceous Period, scientists were able to reconstruct the animal, named Coloborhynchus capito. They found that its skull would have been about 75cm long, making it the largest toothed specimen yet found. Dr Martill told BBC Nature: \"At the end of the Cretaceous, [pterosaurs] became extinct, [they have] no descendants. \"This is why they are so fascinating - all of our knowledge comes from the fossil record. \"The record is very scrappy, but tantalising.\"