09. April 2021

How do creatures transform into a fossil? How do creatures transform into a fossil?

A DFG Research Unit at the University of Bonn published a book on the latest fossilization findings

Anyone who holds a fossil in their hands usually feels respect. After all, the evidence of past living worlds is many millions of years old. It is often possible to tell at first glance whether the fossil is a plant, a shell or even a dinosaur. But what looks like a bone is usually not one at all. Only tiny remnants of the faded creature are contained in it. The form is preserved, but the substance is replaced by minerals, hence the term "petrifaction." How exactly this works is reported by a research group organized as a DFG Research Unit at the University of Bonn in the now published book "Fossilization."

225 million year old "rainbow wood"
225 million year old "rainbow wood" - 225 million year old "rainbow wood" from the Petrified Forest in the US state of Arizona. The colors come from tiny amounts of iron. © courtesy of Dr. Sidney Ash, New Mexico, USA

When laypeople come across a fantastic-looking fossil, they marvel: Oh, what is that? How old is it? How did it get that way? "Scientists are people, too, and they usually ask the same questions," paleobotanist Dr. Carole T. Gee describes her experience in the book's foreword. She is one of a total of 16 authors who have conducted research in recent years in the DFG Research Unit "The Limits of the Fossil Record: Analytical and Experimental Approaches to Understanding Fossilization" at the University of Bonn, which is funded by the German Research Foundation (DFG).

Normally, decomposition begins immediately after death. In a few exceptions, environmental conditions prevent this, for example because it is too humid or too dry. Together, the scientists asked themselves how a living being turns into a fossil after death. "With the naked eye, it is usually possible to see what kind of organism or part of one it is," says paleontologist Prof. Dr. Martin Sander of the University of Bonn, the coordinator of the Research Unit. A dinosaur bone looks like a bone, but its composition is greatly altered. For example, although it has a much higher mineral content than fresh bone, it is not just pure "stone," as was always thought. Rather, the fossil still contains organic molecules derived from the original living being. Even the microstructure of the bones has often survived. "Scientists have been studying dinosaur fossils for 200 years. But we don't know what we actually have in our hands," Sander sums it up.

That's why paleontologists, geochemists, organic chemists, pharmacists, mineralogists, and microbiologists have joined forces in the research group to form a productive community. Using state-of-the-art analytical methods such as Raman spectroscopy and high-sensitivity mass spectrometry, they study the structures and detected traces of original organic matter of living organisms.

Bone cells 290 million years old

Among the surprises was that bone cells, known as osteocytes, and blood vessels were preserved in most of the fossil bone, albeit altered. "We were able to isolate bone cells that are 290 million years old - 40 million years older than before," Sander reports. In addition, the researchers succeeded in using fish fossils to elucidate the steps involved in the metamorphosis from living being to fossil. How wood fossilizes was also suspected before: by hot silicate-bearing waters. However, the scientists have experimentally proven that instead of wood, agate is held in the hand.

The 400 million year old spine of a spiny shark from the Hunsrück Shale, which has a very complex fossilization history, also stands out. The original bone material seems to be partially preserved, but part of the fish has turned into graphite under high temperatures of about 330 degrees Celsius. Incidentally, the slate from the Hunsrück region also "adorns" the roof of the Poppelsdorf Palace and many other old buildings in Bonn.

Written in English, the book is intended as an introduction to fossilization, but also as an interim report of the DFG Research Unit embedded in the Transdisciplinary Research Area (TRA) "Building Blocks of Matter and Fundamental Interactions." In six different TRAs, scientists from a wide range of faculties and disciplines at the University of Bonn come together to work on future-relevant research topics.

If the German Research Foundation continues to fund the research group, the scientists already know which aspects of fossilization they will be looking at more closely in the future: In real time, they want to observe the process of bone fossilization with the Raman spectrometer. They also plan to create "artificial" fossils by precipitating lime and phosphate minerals around animal carcasses. Furthermore, together with pharmacists from the University of Bonn, the team wants to investigate the question of whether the color of fossil flowers can be determined using ultra-sensitive mass spectrometry.

Publication: Carole T. Gee, Victoria E. McCoy und P. Martin Sander (Hrsg.): Fossilization – Understanding the Material Nature of Ancient Plants and Animals, Johns Hopkins University Press, 304 S., 120 US Dollar, also available as e-book

Information about the Research Unit


Departement Paleontology
Institut für Geowissenschaften
University of Bonn
Phone: +49-(0)228/733065

Prof. Dr. Martin Sander
Speaker of the Research Uni
Departement Paleontology
Phone: +49-(0)228/733105




Silicon distribution in the wood cells of a tree from a hot spring:
Two examples of plant pigments that may be found in the fossil record:
Book "Fossilization"
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