The Arén Formation or Arén Sandstone (Catalan: Calcàries i gresos d’Areny) is a geological formation in the Tremp-Graus Basin around Arén, Catalonia, Spain whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation. The formation dates to the Campanian to Maastrichtian and underlies the Tremp Group.

Fossil content

Dinosaurs

Dinosaur eggs (Megaloolithus baghensis, Sankofa pyrenaica), sauropod tracks, unnamed sauropod remains, theropod tracks, euornithopod tracks, and an unnamed iguanodont remains present in Lérida Province.

Paleontological sites of interest

-Les Serretes. It is a place in Vilamitjana municipality known by the finding of an important paleontological site. In this site there have found dinosaur remains that belongs to the Second biggest hadrosaur found in Spain, and the biggest of Catalonia. Also there have been found two carnívor dinosaur tooth that belongs to two new dinosaur species morphotypes. Picture of the dentary from les Serretes. Nowadays exposed on the Museum of Isona.