Paleogeographic map of the Pyrenees region at the end of the Cretaceous.
Author: Oriol Oms
Outcrops of the Tremp Formation around Isona village
Conca Dellà conserves one of Catalonia’s most important collections of palaeontological sites and dinosaur remains. A band of sediments from the Upper Cretaceous crosses Catalonia from east to west at the height of what we call the Pre-Pyrenees, and it is there that the main palaeontological sites from a period stretching from 72 to 66 million years ago can be found. Dinosaur remains have been found in the regions of Berguedà (province of Barcelona), Alt Urgell, Pallars Jussà and la Noguera (Lleida) and also in Ribagorça (province of Osca).
Remains of bones, eggs and footprints of the last dinosaurs to live in Europe have been found, as well as those of other organisms (vertebrates, invertebrates and plants) that lived alongside them.
We must imagine a much different landscape to that of today. The Pyrenees had just begun to form (and they would take more than 20 million years to do so!!) and the sea covered these regions. A drop in the sea level pulled the sea westwards, converting Conca Dellà into an increasingly more continental area with large fast-flowing rivers. Europe was a continent made up of islands with more or less contact between them, which at certain times acted as a step for the new species that would possibly migrate from the Asian continent.
Two great geological formations have been conserved in Conca Dellà: the Gresos d’Areny formation and the Tremp formation. These two formations were deposited just as the Pyrenees mountain range began to rise.
The Gres d’Areny formation is made up of generally very hard sandstone (sands) that appear in sites such as La Posa and originated in areas close to the sea.
The Tremp formation corresponds to zones of transition between the sea and the continent (grey unit) and also to fluvial environments (lower red unit). The end of the Mesozoic period was marked by the presence of layers of limestone (Vallcebre limestone and lateral equivalents) which point to a wide extension of lake areas which, subsequently, in the Palaeocene, gave rise once again to large rivers.
Within the municipalities of Conca Dellà, Tremp or Abella de la Conca, there is a large number of palaeontological sites, containing both fossils of dinosaurs (bones, prints and eggs), and of other vertebrates as well as plant remains. Those providing more information on a scientific and patrimonial level are described below.
Basturs 1 and Basturs 2
These are the most important sites of dinosaur eggs in Conca and one of the most important in Europe. They can be found at the north of the town of Basturs and were discovered during the decade of the 1960s, but the scientific study of them did not begin until the 1990s.
Hundreds of dinosaur eggs can be observed in these sites, especially in the form of circular sections. The eggs measure some 20 centimetres in diameter, and the study of the micro-structure of the shell has helped to classify them within the Megaloolithus genre. This type of egg is considered to belong to sauropod dinosaurs from the titanosaurus group. The rock where these eggs are found also conserves a large amount of small fragments of shells. This fact has helped to define this zone as a recurrent nesting area; in other words, titanosaurs periodically went there to lay their eggs.
This is the site that has yielded most dinosaur skeletal remains to date. It was discovered by an amateur geologist Marc Boada, and the first intervention took place in the winter of 2001. Since then, excavations have been carried out almost every year, and more than 1,000 bone remains have been recovered. These mainly belong to hadrosaurs, while a small number correspond to crocodiles and theropods. Due to the amount of remains conserved, the town of Basturs is considered to be one of the most important dinosaur sites in Europe.
La Llau de la Costa
In this site, located near the town of Basturs, prints of hadrosaurs or duck-billed dinosaurs have been conserved. These fossilised prints correspond to relatively small dinosaurs, since the maximum length of the prints does not exceed 30 centimetres.
A classic site excavated in the 1950s by the team led by Doctor Walter Kühne from the University of Berlin, with Dr Aguirre from the National Museum of Natural History. With the valuable assistance of Mr Nadal and Mr Montaner (the latter was foreman of the coal mine at Suterranya) several remains of a sauropod dinosaur were extracted and sent to Madrid. In the 1980s a new excavation was attempted by the team led by Doctors Josep Vicenç Santafé and Maria Lourdes Casanovas from the Institut Català de Paleontologia Miquel Crusafont, in which members from the Institut d’Estudis Ilerdencs participated. These carried out the tedious task of preparing the soil with explosive experts from the Spanish army, but the meteorological conditions thwarted this second intervention. Then, since the site remained covered, protected and intact, and thanks to instructions from Mr Antoni Lacasa, who took part in the campaign in 1984, this site was located again. Since 2012 a total of 6 excavation campaigns have been carried out, partially funded by the prestigious National Geographic Foundation, indicating the potential of this site. The sauropod fossils extracted are currently being prepared.
Site where tens of footprints attributed to titanosaurs have been conserved. The footprints present two morphologies corresponding to the shape of the foot and hand of the dinosaur that left them. Those corresponding to the feet are large (they can exceed 60 centimetres in length) and oval-shaped, while those made by the hands are small and are half-moon or croissant-shaped.
Molí del Baró
Located very near the town of Sant Romà d’Abella, this important site has produced a wide variety of dinosaur remains and remains of other vertebrates, as well as of invertebrates and plants. The site could correspond to the accumulation of water in an abandoned meander or in an area very close to a river.
The majority of recovered remains belong to different sized hadrosaurs, but teeth of carnivorous dinosaurs, fragments of titanosaurus egg shells and several crocodile bone remains were also discovered. Some recovered remains belong to the shell of land snails from the Lychnus genre. The most abundant remains correspond to remains of different species of plants, most notable of which are the leaves of the Sabalites palm tree. As well as leaves, innumerable fragments of trunks and seeds were also found.
The La Posa site is the most famous locality in the Conca Dellà region and has been adapted for visitors. It consists in a large surface that corresponds to the top of a sandstone bed of the Aren Sandstone Formation. It displays hundreds of depressions with a maximum size of 50 centimeters. Originally, paleontologists thought that the holes corresponded to the tracks produced by sauropod dinosaurs but many features of the locality, such as the coastal origin of the trackbed (with plenty of marine invertebrate), lead the scientists to interpretate the ichnites as feeding traces of rays. Rays are fishes related to sharks featured by a cartilaginous skeleton that feed on the intertidal zones of coasts by producing depressions on the sea floor. They produce holes during the feeding activity, when they feed on marine invertebrates.
The Els Nerets site, located between the villages of Vilamitjana and Suterranya (Tremp municipality), yielded hundreds of fossil remains of a great variety of taxa, including dinosaurs (hadrosaurs, titanosaurs, teropods, nodosaurs), crocodiles and turtles. The site has been excavated recently.
Sant Romà d’Abella
The Sant Roma d’Abella site is found near the homonymous village, in the Isona i Conca Dellà municipality. It was excavated many times during the 1980s and 1990s and later in 2003. The locality is known to yield cranial and postcranial material of a new species called Pararhabdodon isonensis, a lambeosaurine hadrosaur (“hollow-crest” hadrosaurs) of 6-7 meters in body length. Recent studies indicate that most of the “duck-billed” dinosaurs found in the region probably belong to similar species of that from Sant Romà d’Abella, being all of them lambeosaurine hadrosaurs.
Costa de les Solanes
The Costa de les Solanes site was discovered in 2002 by Pere Galceran, a neighbour of Basturs village who knew the work conducted by paleontologists in the nearby Basturs Poble fossil site. Pere Galceran saw some big bone fragments at the margins of a creek and identified them as belonging to dinosaurs. He called scientist of the Museu de la Conca Dellà, who certified the finding and started the administrative procedures in order to conduct and official excavation at the site. The fieldworks were conducted in two consecutive summer campaigns in which paleontologists collected a partial skeleton of a hadrosaur. A preliminary study of the bones indicate that they belong to the largest hadrosaur found in Europe, ataining a body length up to 9 meters.