19 Types Of Fossilization And Their Characteristics

The fossilization is a physical-chemical transformation over hundreds of thousands of years it is suffering the body (whether it is an animal or plant) to convert fossil. This process s
It occurs in exceptional cases, since there must be favorable environmental conditions so that the absence of oxygen, among others and very especially, can occur, the main factor of decomposition when an organism dies.

In addition to the fact that the fossilization process requires many years, it is also a process of a lot of time and patience, discovering and recovering fossils.

Types of Fossilization

Dinosaur fossil

A fossil is called any remnant of animal or plant origin or the impression left by an organism that lived on Earth in very remote geological times and that for various reasons did not disintegrate but was preserved (in its entirety or some of its parts) more or less intact, becoming part of the earth’s crust.

Thanks to scientific studies, explorations and research carried out by Paleontology, many fossils have been discovered and rescued, although it is considered that it is a minimal percentage compared to what is supposed to be still in the deepest layers of the Earth.

Taphonomy is the science that studies the dynamics of the fossilization process, provides paleobiological and geological information that helps to understand the characteristics and reasons for the conservation of the fossil.

Fossils and their transformation process can be classified according to various aspects, which are explained below.

Types of fossilization according to the geological process

Permineralization or petrification

Skull of a petrified velociraptor

It is the process that occurs when the organism or any of its parts are mineralized, forming a faithful copy on the stone. When they die, many organisms end up in the beds of rivers and swamps and are buried by layers of sediment that, in addition, help their conservation.

With the passage of time the organic matter is being replaced by the surrounding minerals, thus becoming petrified fossils.

In general, it is the hardest parts of organisms that are mineralized (bones, teeth and shells and shells of animals), although petrified fossils of eggs, plants and fruits have also been found.


Mosquito preserved in Baltic amber

Inclusion occurs when the organism is trapped within environments or materials that allow its conservation more or less intact to this day. Depending on the conditions, this type of fossilization can be:

  • Gelling or freezing : it occurs in glacier areas. Throughout history there have been different glaciations in which it is assumed that many specimens of various species died and were buried under large layers of ice that allowed their good state of conservation. In Siberia and Alaska, frozen mammoths have been found for more than 25,000 years in a perfect state of preservation, and they can even find food in their digestive system.
  • Mummification:  the organism is preserved thanks to the dehydration that it undergoes due to high temperatures.
  • Conservation in amber or tar:  in this case the organism is “trapped” by the thick sap of a tree that later solidifies, leaving the organism intact, even with its soft parts and all its genetic information. This is also the case when the organism is trapped in tar (crude oil).


Trilobite fossil print

Also called fossilization by compression, imprint or imprint, it takes place when the organism remains on some surface of little or relative hardness such as sand, mud, silt, clay, limestone, etc., and that is then covered by sediments that harden with time, resulting in a two-dimensional impression of the organism or some part of it.

Types of fossilization according to the chemical process


Ammonoid (Ammonoidea) fossils that underwent carbonation, Jurassic

It happens when the hard parts of the body are transformed into calcium carbonate or calcite.


Silicified cross section of a tree trunk

The silica contained in water, sediments or volcanic lava is deposited in the pores and interstices of the body and facilitates its fossilization.


Pyritized Ammonoid (Ammonoidea) fossil, found in Yorkshire, UK

It is when organic matter is replaced by pyrite or marcasite, a product of the combination of iron present in water with hydrogen sulfide that is produced by the decomposition of the body in an environment without oxygen.


Shark teeth underwent the phosphating process and were preserved in sedimentary rocks.

The calcium phosphate present in the bones and teeth of vertebrate animals allows fossilization with the help of calcium carbonate found in rocks and sea and river beds.


Charred fern embedded in a sedimentary rock

During the Carboniferous period of the Paleozoic Era, the earth had large extensions of forests that later degenerated into carbon thanks to particular atmospheric conditions; it is the most common mineralization process for plant species.

According to the physical process that occurs


Dismemberment of the skeletons at the level of their joints, due to the destruction of the ligaments.


Close-up of the back of a velociraptor fossil, showing the fractured ribs

Rupture due to physical impact or predation by other animals, even prior to death.


Fossil of a young Triceratops, you can see how polished its bones

Deterioration or polishing of the bones, softening their shapes and losing details. This can be caused by time, external abrasives, or brittleness in the skeletal structure.


It occurs in marine organisms such as algae or sponges in shallow seas.


The minerals present in the sediments slowly corrode the bones.

According to the presence or not of the organism


When the structure of the organism is present and preserved, although it is transformed to a greater or lesser extent by the mineralization process.


Impression or filling that remains after the organic matter has disappeared from the body. Depending on whether the fossil reflects the exterior or interior of the organism, the mold will be external or internal.

Fossil substances

When high pressures, high temperatures and physical, chemical and geological changes intervene in what thousands of years ago were living beings, transforming them into liquid hydrocarbons (oil), natural gas or coal (graphite, diamonds, calcite, etc.)


Depending on the type of fossilization, fossils of prehistoric animals (such as dinosaurs), marine species (fish, mollusks and marine arthropods), plants (amber, copal or coal) may be found in even ancient hominids and humans.

The term “Living Fossil” can be found in some texts and is the name given to certain species that exist today but are very similar in appearance to species that have already become extinct. It is also used to name specimens that were believed to be extinct and some were later found alive.


  1. Ma. De los Ángeles Gama Fuertes (2005). Biology 2: multicellular biodiversity. Page 224.
  2. Patricia Campos-Bedolla and others (2003). Biology, Volume 1. Pages 82-83.
  3. Fossils Recovered from Investigación.us.es
  4. George Madden (2014). Fossils and types of Fossilization. Recovered from prezi.com
  5. Antonia Andrade. Types of fossil preservation. Recovered from uah.es
  6. Fossil. Recovered from es.wikipedia.org.

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