Ortoceras plate with 2 to 4 cut fossils in each piece.

Orthoceras is an extinct genus of molluscs that lived during the Middle Ordovician. This nautiloid cephalopod had a tapered, cylindrical, cone-shaped shell with closely spaced chambers, containing a concave and a convex septum, with a connecting tube, the sipho, in the center. The length of the shell was approximately 15 cm. Orthoceras was a good swimmer, feeding on carrion and small animals. The shell always remained in a horizontal position while swimming. Fossils include all remains and traces of plants and animals that are preserved in rocks. Although commonly thought, fossils do not have to be 'petrified'. Indeed, many fossils are not fossilized. Even from very old rocks, fossil remains are known that have hardly changed. Furthermore, many think that fossils are always very old. This is also not correct. Many very young fossils are known, originating in periods known to humans. The science that studies fossils is called paleontology. This area of ​​knowledge helps in the study of rock sequence, a branch of geology called biostratigraphy. Because remains of life only fossilize under specific circumstances, fossil information is limited and by definition "incomplete". When we hear the word fossil, people often think of the bones of dinosaurs or mammoths and it is indeed true that the hard parts of an organism have the greatest chance of being preserved through fossilization. For vertebrates these are the bones and especially the teeth. The softer tissues of the organism are preserved only in special cases and are therefore much rarer. Softer tissues are only preserved if they quickly become buried under a layer that protects them against any form of rotting or damage. It is sometimes difficult to get a good picture of the complete organism with only the hard parts. A good example of this is the Conodonta, which were found in large numbers for a long time, but were only known for their teeth. Only when a print of the rest of such an animal was also found did it become apparent that this was a primitive form of the tribe Chordata. In other animal groups, other hard parts, such as shells, are often fossilized. There are a number of special forms of fossilization. For example, complete insects are sometimes found enclosed in amber, because the resin from which the amber is formed forms a good seal against oxidation. This also applies to tar pits on a larger scale. Near the American city of Los Angeles there is a good example of this in the La Brea tar pits. The bones of animals caught in the tar pit were often exceptionally well preserved. Moreover, the trapped animals often attracted predators, which also became entangled. In this way, a "bone cemetery" was formed during the Pleistocene. Very well preserved fossils are often found in clays deposited in stagnant anoxic water. Due to the absence of oxygen, plants fossilize particularly well in this environment. Very often the entire water column is not oxygen-free, but only the lower part. Such stratified water therefore has a normal oxygen content in the top layer. Organisms die in the top layer and then sink to the bottom and end up in an oxygen-free environment where they are preserved. Living organisms can also unintentionally end up in the lower oxygen-free layer, causing them to die and fossilize. In such a deposit, fish are sometimes preserved in a cramped manner, which indicates suffocation. A well-known rock with such fossils is the 'Kupferschiefer' from the Rotliegend in central Germany. In addition to remains that come from organisms themselves, traces that have been actively or passively made by organisms are also considered fossils. This includes, for example, coprolites (fossilized feces) and trace fossils such as paw prints and excavations. It is not always possible to determine from trace fossils which animal they come from. Z