Fossils are traces of living beings that have become more or less mineralized over time. As witnesses of the past, they allow us to reconstruct the most ancient environments. Some places are suitable for fossilization: the Lagerstätten are sites of exceptional conservation, whether in quality, quantity or diversity. Let's take advantage of these unique conservation sites from all over the world to trace the history of life.
The Burgess fauna of the Cambrian
More than 500 million years ago, Gaul was absolutely not entirely occupied by the Romans. At that time, there were no humans, no dinosaurs, not even mammals or land animals! In the Cambrian, only marine animals existed, and the land surface did not have a climate conducive to life. One might think that there were few living species, yet this period experienced a Cambrian explosion, a sudden appearance of new groups of animals very diverse. The very famous and late American paleontologist Stephen Jay Gould said that this anatomical disparity has never been equaled since.
It is possible to observe this diversity in Canada, at Yoho National Park. There, the Burgess fauna delivers us specimens all the more strange than the others, of which some do not have any descendants as of yet. Among them, Anomalocaris, or literally "strange shrimp", is the first known predator of the living world. A large arthropod with large appendages that can reach 1 meter in length, it is known for its large compound eyes. But an even more bizarre animal from its time is the Hallucigenia. It is an animal with a long and thin body like that of a worm, which does not have a clearly defined head. Instead of legs, it has spines on one side of its body, and tentacles on the other side, but none of them seem to be adapted to walking... For a long time, the fossil was represented upside down, walking on its spines, whereas it seems that it moves rather on its tentacles!
Image: Anomalocaris with its two appendages, and Hallucigenia on its rock.
The Fezouata deposit of the Ordovician
Let's jump in time and space. 30 million years later, in Morocco, in the region of Drâa-Tafilalet, walking on dry land was impossible because the place was covered by an immense and deep ocean. Today, the Fezouata deposit offers us the first site of exceptional conservation of the Ordovician, and allows us to better understand this ancient era, known to paleontologists as the Ordovician radiation, the second period of explosion of diversification, different from the Cambrian presented above. Where for years scientists thought the two Cambrian and Ordovician explosions were unrelated, the existence of similar species between the two sites, such as Anomalocaris, suggests that these two explosions were in fact one long one.
In addition to similar species, there are new marine species that were not known from the Cambrian, such as trilobites, the flagship fossils of paleontology. Marine arthropods that disappeared 250 million years ago, are extremely abundant and diverse, with more than 18,500 described species. As a comparison, only 14 species of Homo have been identified to date… Trilobites resemble nothing known today, and are found only in the sea. We find a great diversity in the Fezouata deposit. Other strange species are represented there, like the Eurypterids more commonly called sea scorpions, although they are not related to them. Located at the top of the food chain, some species can reach 2 meters long, and the group is among the largest arthropods that have existed on Earth.
Image: on the left, Eurypterids, on the right, a fossil of Selenopeltis binodosa and its representation
The Rhyne Cherts of the Devonian
Let's go further back in time, and above all, let's go back to dry land: for plants and arthropods have recently emerged from the waters! 100 million years later, in Scotland, the site of Rhynie chert presents silica deposits. When the fauna and flora were in full life, volcanic activity covered everything quickly, freezing the biodiversity. This specific fossilization allows us to have specimens of very good quality, with cellular conservation!
But fossils are not only animals! Algae, fungi and the first traces of lichen can be observed in Rhynie. Among these plants, Aglaophyton is known only in this place, and it is among the first plants to have had a relationship with fungi.
Image: Rhynie chert with Aglaophyton in the foreground. Author: richard bizley
The Mazon Creek site of the Carboniferous
The Mazon Creek site in Illinois, USA, is an exceptional fossil site from 300 million years ago. The quality, quantity and diversity of the fossils make it an important and well known paleontological site, which was once a river flowing in a tropical climate.
Many species have been found, both animal and plant, but the most bizarre is Tullimonstrum gregarium, also known as the Tully monster. It is a soft-bodied animal, no more than thirty centimeters long, which is now designated as the official fossil of the state of Illinois.
Image: Tullimonstrum gregarium. Author: Nobu Tamura
The Solnhofen Limestone of Germany
After a gap of 150 million years, a period during which no exceptional conservation site is listed to date, our journey takes us to the time of the dinosaurs, in the Jurassic. And it is in Germany that the Solnhofen limestones deliver us fossils of exceptional quality. A former archipelago on the edge of the Tethys Ocean, this Bavarian municipality was once covered with a very fine limestone mud, which has preserved species at a remarkable level.
Solnhofen is known in particular for having delivered a very well preserved specimen of archaeopteryx. It is a small dinosaur of about 60 cm in length and 1 kg in weight, whose good preservation has allowed it to show the presence of feathers. In general, archaeopteryx looks very much like a bird (with developed wings and flight feathers, and the presence of a fork, a characteristic bone of birds), with dinosaur characteristics (such as teeth, clawed fingers on the wings, and a long bony tail). The iconic species helped discover that birds are theropod dinosaurs.
Image: representation of archaeopteryx. Author: Simon Stålenhag
Image: representation of archaeopteryx. Author: Simon Stålenhag
The Angeac site from the Cretaceous
Let's fast forward to some 10 million years and go down to France. In the heart of the Charentes region, near Angoulême, the Angeac site offers us a collection of more than 7,000 pieces from over 50 different species dating back 140 million years. Known as one of the largest dinosaur sites in the world, it is also possible to find fossils of plants, turtles, crocodiles, fish, pterosaurs, lizards and amphibians. In 2019, a huge sauropod bone was unearthed, a femur of 2 meters and 400 kg.
The site is well represented in pictures, because Mazan, whose real name is Pierre Lavaud, is a comic book author who has taken a close interest in the site. Since 2010, he has been closely involved in the excavations, transcribing the history and discoveries into images. Thus he represents some species, such as the ornithomimosaurus, the flagship dinosaur of Angeac, 5 meters long (of which 49 individuals have been listed on the site). His comic book "Mimo sur la trace des dinos" (Mimo on the trail of the dinos) tells the story of the discovery of the site, and contains drawings of the excavations themselves as well as reconstructions of the landscape.
Image : representation of the Angeac site 140 million years ago. Author : Mazan
Image: An ornithomimosaurus from the Angeac site. Author : Mazan
Rancho la Brea, a Pleistocene site
For this last jump in time, the dinosaurs disappeared following the impact of a meteorite, and the mammals had time to diversify. It is in the heart of Los Angeles that Rancho la Brea offers us fossils of the Cenozoic. Imprisoned in bitumen, species dating from 12,000 to 40,000 years ago are gradually coming back to the surface. 95% of the species of this site are insects, but we also find spores and pollens (useful to reconstruct the paleoenvironment of the Pleistocene), and some mammals. Among the latter, mammoths, sloths and saber-toothed tigers inspired the famous animated film Ice Age. A fun opportunity to review your fossils!
Image: A complete saber-toothed tiger fossil found at rancho la brea. Author: James St. John
It is impossible to list all the exceptionally preserved sites in the world, as there are actually about 50 of them, not to mention that these exceptional sites are not the only ones with fossils! Take a walk along the beaches, and chances are that the coasts will offer small paleontological surprises.
For the pleasure of the eyes, sites of paleoartists: