The meaning of Paleontology: "What is a fossil"
Paleontology is the Science that studies life in the past. The term was coined in the first half of the 19th Century (from the Latin paleos =ancient, ontos =life, logos =speech) and it literally means “speech on ancient organisms”.
Fossils are documents that enable the reconstruction of past models of life. They have preserved themselves until modern times by means of fossilization processes.
Fossils are any remains of animals or plants that lived in ages before our current one or any trace that an organism has left in the rock layers, including traces of its activities such as tracks, moulds, signs of movement, etc.
Fossils are found inside rocks that form the most superficial part of the earth’s crust. These organisms have fossilized in different ways but all lived in ages before our current one of today.
Being remains of ancient organisms, fossils are precious witnesses of the Earth’s past. They are scientific objects that enable us to reconstruct biological, geological and geographical events through their study.
Their geochronological significance is very important. Indeed, they have enabled us to understand the historical evolution of the Earth. Of particular and significant interest are “guide fossils”, which have had a short life but a large geographical distribution. Having been found in rock layers located even very far away from each other, they have enabled scientists to attribute to the rocks the same age. The fossilization process of an organic remain starts straight after its death.
The first step of this process is the " post mortem transport", a very common and varied phenomenon that leads to the fossilization of organisms in very distant places and often very different environments from the ones in which they lived.
By studying fossil associations you can understand whether the fossilization environment was the same as the one in which it lived (autochthonous fossil) or not (allochthonous fossil). Naturally, the transport phenomenon verified more probably for organisms that could freely move (nektonic marine organisms, birds) rather than for those that were fixed to the substratum (e.g. corals).
After the transport, the disintegration process starts. This is mainly due to three types of agents: biological, mechanical and chemical which act with variable speed and modalities on the different parts of the organism.
Most of the fossils that have preserved until today are only composed of "hard parts", that is to say those generally composed of calcium phosphate, silicon or other organic substances such as chitin and keratin since the "soft parts", which are mainly made up of proteins and carbohydrates, go through a fast chemical decomposition.
In order for an organism to preserve itself as a fossil, it must be protected from the action of exogenous agents, in other words a rapid and abundant sedimentation must take place to cover the organic remain before it is completely destroyed. Its preservation greatly depends on the type of sediment that incorporates it. Indeed, fine sediments with a poor permeability, such as clay and marl, offer a much higher protection than the coarser and more permeable sediments (sand and gravel).
The most adequate environments for the preservation of organisms are mainly the marine ones (except the coast) and the continental lakes and marshes.
The preservation takes place according to various more or less frequent fossilization processes.
Mineralization is a very common chemical-physical process in which the mineral substances abundantly contained in the fluids that circulate in the sediments replace the organism’s organic matter completely. The mineral substances that more often become part of the mineralization process are calcium carbonate, calcium phosphate and silicon. Carbonification, a less common process than the previous one, most of all regards plants which, once they are deposited, are attacked by particular bacteria that eliminate the oxygen and nitrogen, indirectly enriching the organic remains into carbon. This is how the great "fossil coal" deposits of the Carboniferous period originated. A third fossilization process, not widely spread and limited to recent organic remains, is encrustation. This occurs when the calcium carbonate, abundantly contained in some type of flowing waters, falls and rapidly deposits on the organic remain. Once it has decomposed, only the mould remains showing its shape. Finally, a very rare process exists named distillation. The volatile elements that compose the organic remain distil, leaving a thin layer of carbon that reproduces its shape. Fossils obtained by distillation are usually poorly preserved. Apart from the described processes, there are cases in which unique conditions (ice, amber, etc.) have allowed the preservation of organisms or of the “soft parts” that usually do not fossilize.
Classification of fossils
Systematics is the science that studies organisms and their similarities, differences and reciprocal relations.
Classification is an arrangement process based on the systematic study of animal or plant organisms. In other words it arranges individual specimens that have common features into categories called “systematic units”.
A given specimen or a group of organisms are defined by identifying or attributing them to a certain category. Systematics is a science made up of strict rules that are collected in the International Zoological Nomenclature Code (4th Edition, 1999). Its articles state the modalities that need to be followed for a correct nomenclature of organisms, for a regular description, etc.
The nomenclature, or the attribution of names according to international regulations, is based on the systematic method enunciated by Linneo in 1758, which was later slightly amended. This classification method is constructed according to a hyerarchical scale that includes a certain number of steps that start general and become more and more specific: Kingdom, Phylum or Type, Class, Order, Family, Genus and Species. In particular, each organism is defined with a double Latin name in which the first part is the genus and the second the species to which it belongs. The double scientific name is followed by the name of the author who defined the species for the first time.
Below is an example of mammal classification:
- Phylum Vertebrata
- Class Mammalia
- Order Perissodactyla
- Suborder Hippomorpha
- Superfamily Equoidea
- Family Equidae
- Genus Equus
Species caballus