Why scientists spent 70 days watching fish rot

British researchers conducted experiments to observe the carcasses of dead sea bass that rotted for 70 days. In the course of their work, they gained some interesting insights into how (and why) the soft tissues of internal organs can be selectively preserved in fossils. What is said in a new work published in the journal Palaeontology.

Most fossils are bones, shells, teeth, and other forms of “hard” tissue, but occasionally rare fossils are found that preserve soft tissue such as skin, muscles, organs, and even the occasional eyeball.

According to Clement et al., no previous study has aimed to document pH (acidity) gradients associated with the breakdown of specific anatomical features as a carcass rots in real time; past experiments have focused on recording pH fluctuations outside of the carcass. So the team decided to fill this gap and conduct experiments on decomposing fish, documenting the change in pH gradient over a period of two and a half months.

They first acquired several adult European sea bass that had died no more than 24-36 hours ago. The fish were kept on ice to slow down the decomposition process, but not frozen to avoid cell damage. They then inserted pH probes into various locations on each sea bass carcass to study specific organs: the stomach, liver, intestines, and epiaxial muscle. The fifth probe was used to monitor environmental pH at a distance of 1 to 2 mm from the carcass.

The entire setup was placed in a container filled with artificial sea water, and the container was placed in a large water bath to minimize temperature fluctuations. The probes were connected to an external electronic reader, and data was recorded every half an hour during the entire experiment.

By day 70, the carcasses had completely disintegrated, “leaving fragments of skin, scales, gelatinous white matter, bones, and some intact fin rays,” the authors write.

The results of the study showed that the organs do not create a special microenvironment – they all rot together in a kind of “soup”. “This means that the likelihood of organs turning into fossils is determined by the specific chemical composition of the tissues,” the authors concluded.

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