Tech UPTechnologyHow to make a fossil?

How to make a fossil?

It is impossible for the imposing stone skeleton of a Tyrannosaurus rex to go unnoticed by those who contemplate it. Sue, that’s what they call the best preserved rex remains to date. Such a figure, more typical of science fiction than of our reality, had a complex transformation process so that it could end up in an exhibition at the Field Museum of Natural History in Chicago millions of years after having fallen to the ground lifeless. Based on this specimen, it may seem easy to find fossils to study to reconstruct the past, but the process of fossilization is extremely rare and, of course, finding a skeleton as complete as Sue’s is an exceptional find for humanity. . We tell you what you have to do if you want to leave a fossil as complete as Sue’s for paleontologists to come.

Taphonomy (which literally means “the laws of burial”) is the branch of paleontology that studies the processes of fossil formation. To make one, you would first have to be clear about what a fossil is. The word comes from the Latin fossilis, which means “which is obtained by digging”. This etymology already gives us an important clue. The first two meanings that the dictionary of the Royal Spanish Academy has for the word “fossil” are the ones that interest us: “said of a substance of organic origin or of a remnant of an organism: that it is more or less petrified, and it is found due to natural causes in the terrestrial layers, especially if it belongs to another geological epoch”. And also “said of an impression, a vestige or a mold: that denotes the existence of organisms that are not from the current geological era”. More clearly: “fossils are the remains of organisms or their biological activity that have been preserved in rocks, generally in sedimentary rocks”, in the words of Laura Domingo, PhD in Geology and Paleontology from the Complutense University of Madrid. In other words, a fossil is not only a petrified living being, but if any of its activities left a record, it would also be a fossil. Therefore, not only is a T yrannosaurus rex a fossil, but so is a footprint, excrement, a tree trunk, a leaf, eggshells, or a feather.

If you wanted to make a fossil, you would need to generate a series of conditions and processes that in the natural course of life of organisms are difficult to achieve successfully. There are various forms of fossilization : among other options, the organism could be frozen or preserved in amber. But the basic process of most of the fossils found is based on burial. Therefore, the organic remains to be fossilized must remain under sediments (mud, sand, rocks, for example) as soon as possible. Not a little, no. If possible, tons of mud that isolate the body from everything that can deteriorate it: the wind, water movements, animals that come to eat the remains and even the oxygen itself, in order to slow down decomposition. The less exposed and the more preserved, obviously, the more chances of success. Therefore, do not bury it under a waterfall, on top of a mountain, or leave the remains next to a pack of hyenas. You need a place like the bed of a river or the bottom of a lake.

After this first phase, you only have to wait thousands of years for the remains to undergo mineralization . This chemical process causes organic remains to turn to stone. The pressure of the sediments on the organism will squeeze out the water and dissolve all the organic components, replacing the bones with other minerals. In time, what will be left will be a stone copy in the shape of the buried organism. It is easier to preserve the hard parts such as bones, teeth or shells, but, with a bit of luck, you will be able to preserve soft parts of organisms such as feathers, hair and algae.

Nature tends to feed on itself. Getting an animal to stop serving as sustenance when it dies and be preserved for millions of years is a remote coincidence. This makes fossil finds extremely important given the few options available to study them and continue to piece together the puzzle that answers one of the universal questions of human beings: where do we come from?

A study by the Higher Council for Scientific Research (CSIC) analyzed bone remains in the Doñana National Park to better understand the formation of the fossil record. The research was published in the journal PLoS ONE, adding information on these processes as similar projects are already doing in the Amboseli National Park (Kenya) or the Yellowstone National Park (United States).

“For fossils to exist, one must start from the presence of skeletal remains produced by animals in ecosystems. These remains will undergo a series of processes and modifications that can lead to their preservation in the fossil record or their destruction before they have the opportunity to fossilize. With this project we intend to better understand the processes that lead to fossilization in the order in which they actually occur and not the other way around, which is what paleontologists usually do when we study a fossil deposit and try to construct how it was formed”, he commented. Soledad Domingo, team researcher, about the work in Doñana.



Behrensmeyer, AK et al. 2000. Taphonomy and Paleobiology. Paleobiology 26(4): 103–147. DOI: 10.1666/0094-8373(2000)26[103:TAP]2.0.CO;2.

Domingo, MS et al. 2020. Taphonomic information from the modern vertebrate death assemblage of Doñana National Park, Spain. PLoS ONE 15 (11) : e0242082. DOI: 10.1371/journal.pone.0242082.

Fernández-López, SR 1999. Taphonomy and fossilization. Treaty of Paleontology, volume I, pp. 51-107. Superior Council of Scientific Investigations.

Pardo, A. 1996. Fossils and fossilization: processes and results of the long underground history. SEA Bulletin , 16, pgs. 31-42.

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