‘Mummified’ dinosaur sheds light on how soft tissue can be preserved for millions of years

The term “mummy” is often used to describe rare dinosaur fossils with extremely well-preserved skin (and sometimes other soft tissue). It is generally considered that such fossils can only form in exceptional circumstances: in particular, the carcass must be protected from the weather and from agents of decomposition, such as predators and scavengers – which implies the extremely rapid burial of the corpse. Once covered in sediment, the animal’s remains were theoretically protected from the elements and scavengers. Insects, fungi or other micro-organisms living underground could nevertheless attack the carcass, which calls into question this hypothesis of rapid burial. A recent analysis of the remains of a relatively well-preserved dinosaur suggests the existence of another pathway for soft tissue preservation.

A partially ‘cleaned’ dinosaur carcass

The Dakota specimen studied here, from the hadrosaurid family, was found in the Hell Creek Formation, dating from the Late Cretaceous; he has large patches of parched skin on his limbs and tail. CT scans showed that this preserved skin was deflated, not compressed by the sedimentary stones covering it.

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At the top, an illustration of an Edmontosaurus; below, the “mummified” forelimb belonging to the dinosaur Dakota. Credits: Natee Puttapipat/Drumheller et al., PLOS One, 2022

Read also: A mummified baby mammoth, found in the ice in Canada!

The study of the sediments surrounding this fossil shows that this dinosaur lived in a rather humid environment; when he died, his body lay near a water source. In addition, the team identified soft tissue damage consistent with injury likely caused by predators or scavengers. These are the earliest examples of unhealed damage caused by carnivores to the skin of a fossilized dinosaur. These tracks prove that the dinosaur carcass lingered in the landscape for some time before it was buried.

How to explain then that his skin did not rot as it should have? To answer the question, the researchers combined fossil evidence and sightings of modern animal carcasses. The latter are often emptied by scavengers and decomposing animals, which attack the internal tissues and leave behind skin and bones. The study authors propose that damage to this dinosaur’s skin would have exposed its innards, allowing a similar process to occur; the skin and bones then slowly dried out before burial.

A common process in the forensic literature

Based on bite marks – likely caused by ancient crocodilians – researchers believe that at least two carnivores consumed parts of a limb and tail of the dinosaur after it died. As the viscera were devoured or rotted, the tough, scaly skin of the hadrosaurid was then better able to dry out in the sun, forming a kind of envelope around the bones before the animal was buried – which explains the “deflated” appearance of the skin.

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Traces of injuries have been identified in three different places, here in the soft tissues of the right hand (left), and the right elbow (right). Credits: Drumheller et al., PLOS One, 2022

Read also: Huge dinosaur skeleton found in Portugal

Incomplete evacuation of the carcass allowed gases, fluids and microbes associated with decomposition to escape, allowing the more durable soft tissue to persist for the weeks or months required for desiccation, before incineration and fossilization “, detail the researchers in PLOS One. This dual process, which the authors call “desiccation and deflation,” is common with modern carcasses.

It’s something that’s actually quite predictable in the forensic literature. said Stephanie Drumheller, a paleontologist at the University of Tennessee at Knoxville and first author of the study. This was simply not considered in the case of dinosaur fossilization; this process explains how dinosaur mummies can form under relatively ordinary circumstances.

Several possible ways of mummification

The researchers point out, however, that not all dinosaur mummies form this way, although it is the most common route; there are probably other ways in which a dinosaur could undergo a process of mummification.

Some mummies may have formed from a quick burial of the carcass, as scientists have believed so far – although, for now, the evidence is lacking to support this theory. Others may have formed by immersion in deep water with little oxygen – a process the authors call “aqueous anoxia”: the lack of oxygen would slow the process of decomposition, allowing mummification to take place. ” Aqueous anoxia itself can promote soft tissue mineralization, contributing directly to the process of fossilization “says the team. This mode of preservation was illustrated by a mummified specimen of the Borealopelta dinosaur.

Read also: How could a fetus have been preserved for 2000 years in an Egyptian mummy?

This new study thus suggests that there could be a lot more mummified skin to be found in the fossil record than previously thought. A real godsend for paleontologists: “ Not only has Dakota taught us that durable soft tissue like skin can be preserved on partially devoured carcasses, but that soft tissue can also be a unique source of information about other animals that have interacted with the carcass. “Says Clint Boyd, senior paleontologist at the North Dakota Geological Survey and co-author of the study.

The team intends to find more of these mummified specimens to study in detail the chemical reactions involved in this process. Researchers also hope to determine why most of the preserved skin remains discovered so far belong to hadrosaurid dinosaurs…

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