Fossils are material proofs of living organisms in the geological past. They are usually found into sedimentary rocks. They allow to know the age of these rocks and the environmental characteristics of the area when these organisms were alive. The source of the most common and known fossils in Bages is the sea. They come from the living organisms of the former, not too much deep, warm sea that covered the region during most of the Eocene period. Fossils can also be found in rocks of lake origin. Fossils of terrestrial vertebrates from quaternary period have been dug up in fluvial terraces (i.e. elephants) and in Toll caves (coves del Toll) in Moià (i.e. bears, hyenas, rhinoceroses.).
I n terms of Geology, the fossils of Bages are recent , thus most of them are similar to the current species.
Hereafter, there is a description of the fossil groups that are common in Bages. However, in the area there are also fossils of vegetable remains, sponges, bryozoans, worms, crabs, shark teeth, turtle shells, sirenid bones.
Nummulites are one of the most typical fossil groups of the marine Eocene. Their popular name is lentils or coins, because of its shape like a lentil. In some places of Bages, they outcome detached in loamy plots of land where they can generously be collected. Also nummulites are the main component of a compact rock: the Sant Vicenç limestone which is actively exploited as stone for ornamental and construction purposes.
Nummulites became extinguished at the end of Oligocene. They were giant marine protozoans -from few millimeters till 6 cm diameter- of the faraminifer group, with the body covered by a calcareous shell. The studies of the nummulites by Dr. Valentí Masachs contributed to to date the different levels of the Eocene of the region.
Corals are colonial marine animals that secrete a calcareous skeleton. Coral reefs, this are the big, calcareous, submarine buildings that are almost made by the skeletons of these animals and where life shows a peak of high biodiversity, growth only in clear, low mineral nutrients containing, warm sea waters (minimum winter temperature higher than 15ºC). The fossil coral reefs outcome in line from north-east to south-west in Bages. They proof the past tropical climate in Catalonia along the Eocene. The fossil fauna of the coral outcrops in Bages (Manresa, Navarcles, Calders.) is quite similar to that of the current coral reefs.
Bivalves (shells, mussels, oysters.) are mollusks provided with a calcareous shell of two valves that are inserted by a hinge. During the Eocene, a lot of bivalves lived in the muddy sea bed close to the coast and to the fluvial mouths. The best preserved fossils of Bivalves belong to the families with thicker and bigger shells. Fossils of families with thinner shells are often just their external or internal moulds.
The diversity of fossils of gastropods (snails) is noticeable in Bages. Their shapes vary from shells with just few turns (Velates, Natica, Terebellum) to very twisted shells (Turritella, Melanoides) and to giant snails (Campanille, Cerithium).
Most of gastropods fossils that are collected in Bages lived in the sea. However, the snail on the photo is one among the few fossils that are found in the layers fom continental lake origin. rocks.
Sea urchins are the most frequent echinoderms in this region. They are strictly marine invertebrates. Sea urchins have an external, calcareous skeleton that is made by welded plates and protuberances where prongs are articulated. They are one of the most attractive fossils of Bages, because they are usually entire and well-preserved. Their shapes are more or less globular or flattened, with radial or bilateral symmetry.
[Oriol Oms, Florenci Vallès, Josep Biosca and Joaquim Sanz]