Arén Dinosaurs inhabited for more than seventy-five million years. Today, their fossilized footprints and the remains of his bones are visible in the local paleontological sites, surprising for its condition.

The first species of dinosaur, which paleontologists from the University of Zaragoza found remains, was named "Arenysaurio". In December 2010 there was a surprising new finding: Balsisaurio bones, a species whose only known remains in Asia and America.