The Orígens Geopark includes a wide representation of the evolution of life on Earth, comprising deposits from the Silurian to the Paleogene, about 400 million years represented by fossils of vertebrates, invertebrates and plants.
Fossil remains of graptolite are recorded in SILURIAN slates. Furthermore, DEVONIAN limestones contain marine fossils that record the extinction of organisms such as trilobites.
The PERMIAN and the TRIASSIC outcropping as reddish bedrock on the northern sector of the Geopark 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 discoveries remind us of the exuberance and variety of the Permian ecosystems.
The next period with a broad paleontological representation corresponds to the LOWER CRETACEOUS, with the outcrops in the Montsec Range recorded in the lithographic limestone quarries of Rubies and La Cabrúa. These have given magnificent fossils of insects, marine invertebrates, plants, vertebrates such as amphibians, small reptiles and even feathered birds. Soft parts of the body are often preserved, as well as rare 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 from these outcrops in 1902 by Charles René Zeiller.
The well-known paleontological legacy comes from the UPPER CRETACEOUS transitional sediments thanks to the abundant dinosaurs remains. This period has provided an excellent record both of coastal environments (rudists accumulations in Collades de Basturs), transitional environments (the ray feeding marks in La Posa) and especially of continental environments (Conca de Tremp and Sallent River Valley in Coll de Nargó) where many dinosaur remains have been discovered.
The existence of dinosaur remains in the Tremp Basin was first notified in 1916, during the building works of the Sant Antoni reservoir. However, the first dinosaur remains were reported in 1954 by German palaeontologist Walter Kühne from an excavation in the Orcau stream (site now known as Orcau-1) along with Spanish palaeontologist Emiliano Aguirre. A few years later, the French palaeontologist Albert-Félix de Lapparent discovered the first dinosaur eggs along the Basturs ravine.
Since the 1980s, researchers from the Catalan Institute of Palaeontology Miquel Crusafont (ICP) and the Conca Dellà Museum have been excavating systematically the area and have been collaborating with related regions, such as Haţeg Geopark (Romania). New deposits with thousands of fossils discovered during this period have contributed significantly on the understanding of the Dinosaurs Age ending in Europe.
The sedimentary strip that records Maastrichtian environments displays a great quantity and quality of bones, eggs and tracks of the last dinosaurs that lived in Europe few million years previous to their extinction on the Cretaceous/Paleogene boundary. Should be noted the discovery of various forms of sauropod, hadrosaurs, or ornithopods or theropods dinosaurs, besides the presence of crocodiles remains, pterosaurs, turtles, and other vertebrates. The wealth of fossilized eggs, both in the Conca de Tremp and the Coll de Nargó area places this region as the main European dinosaur eggs site and one of the most important in the world. Dozens of scientific articles published in scientific journals support the importance of these findings. The recovered fossils are deposited for further research and displayed in the Conca Dellà Museum in Isona and its satellite museum, the Dinosfera interpretation centre in Coll de Nargó.
The sedimentary record including fossil remains is completed with PALEOGENE deposits. The basins north and south of the Montsec Range comprise sites with spectacular concentrations of invertebrates, such as the Geozones of La Règola in Àger or the Ilerdian stratotype west of Tremp. On the other hand, the first mammalian forms, among which stand out the first European primates, have been recovered from Eocene deposits in Àger and la Pobla de Segur.