Flying lizards from the time of the dinosaurs may have grown as big as modern fighter planes, new discoveries are beginning to show.
Pterosaurs were alive between 220 and 80 million years ago, and recent fossil finds suggest their wingspans could reach a massive 18 metres wide.
Today's biggest bird, the wandering albatross, only gets to about 3.5m.
It's thought the reptiles got so big because they simply didn't stop growing as they got older.
Talking about people's growth, Dr David Martill, of the University of Portsmouth, said: "We get to teenage years and we stop.
"But if a pterosaur kept on growing then the older it got, the bigger it got.
"They would be rare as big ones, though, because the older you get, the more chance you have of being eaten or being involved in an accident."