These researchers watched dead fish rot for 70 days—for the sake of science


Oric Lawson / T. Clement and others.

Science can sometimes be a messy endeavor – not to mention “disgusting and smelly”. This is how British researchers describe their experiment of observing a 70-day decomposing sea bass carcass. In the process, they gained some interesting insights into how (and why) the soft tissues of internal organs could be selectively preserved in the fossil record, according to new paper Published in the Journal of Paleontology.

Most fossils are bones, shells, teeth, and other forms of “hard” tissue, but rare fossils are occasionally found that preserve soft tissues such as skin, muscles, organs, or even eyeballs. It can tell scientists so much about aspects of the biology, ecology, and evolution of ancient organisms that skeletons alone cannot. For example, earlier this year, Create a researcher Highly detailed 3D model of a 365 million year old ammonite fossil from Jurassic period by incorporating advanced imaging techniques, Reveal the inner muscles which has never been observed before.

“One of the best ways soft tissues can turn to stone is when they are replaced by a mineral called calcium phosphate (sometimes called apatite),” Co-author Thomas Clements said: from the University of Birmingham. “Scientists have been studying calcium phosphate for decades trying to understand how this process occurs — but one question we don’t understand is why some internal organs seem more likely than others.”

In particular, the muscles, stomach, and intestines tend to “phosphate” more often than other organs, such as the kidneys and gonads. There are two general hypotheses to explain this. The first is that different organs degrade at different rates, and that the pH of some organs will drop below a critical threshold of 6.4. When these organs degrade, they create a different pH microenvironment that increases the potential for these organs to harden. Different minerals can form in different areas within the same carcass.

Examples of soft tissue phospholipids in fossils: (a) A frog's stomach with a phospholipid vacuum;  (b) Micro-CT image of a Brazilian fish fossil with pharyngeal internal organs;  (c) Colobrid snake with phosphate shell.
Zoom in / Examples of soft tissue phospholipids in fossils: (a) A frog’s stomach with a phospholipid vacuum; (b) Micro-CT image of a Brazilian fish fossil with pharyngeal internal organs; (c) Colobrid snake with phosphate shell.-

The second hypothesis is that tissue biochemistry plays a major role. In particular, a diffuse pH environment is formed within the body cavity and persists until the carcass is damaged.

According to Clement and others. , no previous studies have focused on documenting the pH gradient associated with the decomposition of specific anatomical features where carcasses degrade in real time; Previous experiments focused on recording off-carcass pH fluctuations. So the team decided to fix this gap and ran experiments on decomposing fish, documenting how the pH gradient changed over two and a half months.

First, they buy some mature European seabass from a local fishmonger as soon as possible after death (no later than 24-36 hours). Fish are kept on ice to slow decomposition but not frozen to avoid cell damage. Next, they inserted pH sensors at different locations on each of the six sea bass carcasses to target specific organs: stomach, liver, intestines, and axial muscles. The fifth probe was used to monitor the pH of the ambient environment between 1 and 2 mm of the carcass.

More examples of phosphatidylar soft tissue in fossils: (d) phosphatidylcholinester polychords;  (e) Trilobites with phospholipids in the intestinal tract;  and (f) a vampyropod octopus under UV light to demonstrate a phospholipid network.More examples of phosphatidylar soft tissue in fossils: (d) phosphatidylcholinester polychords;  (e) Trilobites with phospholipids in the intestinal tract;  and (f) a vampyropod octopus under UV light to demonstrate a phospholipid network.
Zoom in / More examples of phosphatidylar soft tissue in fossils: (d) phosphatidylcholinester polychords; (e) Trilobites with phospholipids in the intestinal tract; and (f) a vampyropod octopus under UV light to demonstrate a phospholipid network.-

T. Clements dkk., 2022

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