The footprint was found among a series of tracks made by the ancestors of crocodiles and dinosaurs, a group known as archosauromorphs, the researchers from the Autonomous University of Barcelona and the Catalan Institute of Palaeontology said in a statement.
The scientists dubbed the new species of reptile Prorotodactylus mesaxonichnus in an article published in scientific journal Plos One.
They believe the species looked like a crocodile but with wider legs and was about a metre-and-a-half (five feet) long.
The researchers said the footprints suggest the tracks which they found in the Pyrenees mountains in northeastern Spain on the border with France were made by animals that used all four limbs to walk and often also left marks with their tails.
"The new Pyrenean footprints indicate that these animals used all four limbs to walk and often also left marks with their tails," said Catalan Institute of Palaeontology researcher Josep Fortuny.
The researchers believe the archosauromorphs dominated the river beds of the ancient Pyrenees. They said they are now looking for fossilised bones of the animals that made the tracks.
At the time, the Earth was very different from today, with continents grouped into one supercontinent called Pangaea and the planet was recovering from a mass extinction that wiped out most animals.
About 252 million years ago, a mass extinction devastated life on land and in the oceans. Some 90 per cent of species disappeared.