Over the course of the last year, the BBC has been following researchers from the University of Portsmouth as they have been building giant pterosaur models.
The life-size models of the flying creatures - the largest of which has a wing span of 10m - will eventually go on display at the Southbank Centre in London for the Royal Society's Summer Exhibition.
While the fossil record has helped the team put the models together, deciding on the last fine details is tricky. What colour would the pterosaurs have been? Would their eyes be more lizard-like or crocodile-like? Were they scaly, furry and feathered?
Here, palaeo-artist Dr Mark Witton explains how the team has re-imagined the creatures that once dominated the skies millions of years ago.