The area of the Geopark includes a wide representation of the evolution of life on Earth, ranging from deposits from the Permian to Paleogene, nearly 250 million years represented by fossils of vertebrates, invertebrates and plants
The existence of dinosaur remains in the Conca de Tremp (Tremp Basin) was notified for the first time in 1927. The first dinosaur remains in this area were announced in 1954 by German palaeontologist Walter Kühne, who excavate along with paleontologist Spanish Emiliano Aguirre Precipice Orcau (site now known as Orcau-1). A few years later, the Frenchman Albert-Félix de Lapparent discovered the first dinosaur eggs at Basturs ravine.
Since the 80s of last century, researchers from the Catalan Institute of Palaeontology (ICP) and the Museum of Isona i Conca Dellà excavate systematically the area, where new deposits have been discovered and thousands of fossils, which have allowed a better understanding of the end of the Dinosaurs Age in Europe.
Permian and Triassic are represented on the northern edge, where reddish sediments arise. They have provided a wealth of footprints (tracks and traces), mainly reptiles and amphibians, which indicate the great diversity of vertebrates in this area. In terms of plant remains, recently studied new sources remind us of the enormous exuberance and variety of the Permian ecosystems.
The next period with broad representation corresponds to the Lower Cretaceous, with outcrops of the Serra del Montsec, including quarries of Rubies and La Cabrúa, lithographic limestone deposits have provided a magnificent fossils of insects, marine invertebrates, plants, vertebrates such as amphibians, small reptiles and even birds with feathers. Soft parts of the body are often preserved and in some cases even coloration patterns. It is worth mentioning the remains of the first flowering plants (Montsechia vidalii), which appeared on the planet about 130 million years ago and were described in the Serra Montsec in 1902 by Charles René Zeiller.
Perhaps the most active paleontological comes from the Upper Cretaceous transitional sediments thanks to the abundant remains of dinosaurs. This period has provided an excellent record both of coastal environments (rudists accumulations of Collada de Basturs), transitional environments (site of brands feeding herds of La Posa) and especially of continental environments (Conca de Tremp and Sallent River Valley in Coll de Nargó). Bones, eggs and tracks of the last dinosaurs that lived millions in Europe previous to the extinction that took place on the Cretaceous / Paleogene edge, are in great quantity and quality in the sedimentary strip that records environments of Maastrichtian.
Note the presence of various forms of sauropod, hadrosaurs, or ornithopods theropods dinosaurs, besides the presence of the remains of crocodiles, pterosaurs, turtles, and other vertebrates. Wealth remains of eggs, both in the Conca de Tremp and Coll de Nargó place this area as the main European site of dinosaur eggs and one of the most important in the world. Dozens of scientific articles published in journals support the importance of the findings, which are deposited by their conservation and study at the Isona i Conca Dellà Museum and its satellite museum, the information centre Dinosfera in Coll de Nargó.
The sedimentary record with fossil remains is completed with the following geologic period, the Paleogene. On both sides of Montsec there are spectacular concentrations of invertebrate fauna, for example at the geozones of Régola (Ager) or at the Ilerdian Stage, while mammals’ first forms, with particular relevance to early primates Europeans have found in Eocene deposits at Ager and Pobla de Segur.