Decomposing fish help solve the mystery of how soft tissue fossils formed

New research at the University of Leicester has transformed scientists’ understanding of how spectacular fossils form with delicate soft tissue.

While most fossils are “hard” tissues, such as bones, shells or teeth, some rare web pages in the world featured unique elements that allowed minerals to fossilize soft tissues such as skin, muscle groups and other organs – even the fragile eyeballs of some ancient creatures..

But one aspect of this preservation rare that has troubled scientists is why some internal organs seem to fossilize more frequently than others.

Researchers at the Leicester Paleobiology Center have developed an experiment to study the chemistry inside a decomposing fish and map the pH levels of its organs s during carcass decomposition for two and a half months.

Their findings, published today (Monday) in Paleontology, show that the specific tissue chemistry of each organ governs its likelihood of being replaced by minerals.

This finding explains why some tissues are more easily transformed into calcium phosphate fossils that capture the high-resolution detail of the most fragile material of a creature, while other organs are apparently lost to time.

Dr Thomas Clements, now of the University of Birmingham, has led the study while a PhD researcher at Leicester. He said:

“One of the best ways soft tissue can transform in rock is when they are replaced by a mineral called calcium phosphate (sometimes called apatite). Scientists have been studying calcium phosphate for decades to try to understand how this process occurs – but one thing we just don’t understand is why some internal organs seem more likely to be preserved than others.

“We designed a rotting fish viewing experiment that was disgusting and smelly, but we made an interesting discovery.

“Organs don’t generate special microenvironments – they all rot together in a kind of ‘soup’. This means that it is the specific chemistry of organ tissues that governs their likelihood of turning into fossils.”

For a tissue to be phosphated, its pH must fall in below about pH 6.4. At this acidity, if the fossil is buried quickly, calcium phosphate and other minerals can begin the process of fossilization which preserves the exquisite detail of certain soft tissues.

L One of the finest examples of such fossils includes a Cretaceous octopus of the extinct Keuppia style discovered in Lebanon, estimated to be at least 94 tens of millions of years old. ‘years.

Sarah Gabbott is professor of paleobiology and co-author of the article. Professor Gabbott added:

“Observing and recording (and smelling) how a fish rots may not be most people’s idea of ​​the science, but for paleontologists, understanding the process of decomposition is important in revealing what anatomical features of an animal are likely to become a fossil, and what they will become. look like.

“We were really pleased with the results because we can now explain, for example, why fossils often preserve an animal’s gut but never preserve its liver .”

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