doi.org/10.1126/science.adw3536
Credibility: 989
#Dinosaurs
About 66 million years ago, a group of herbivorous dinosaurs died during a drought, just hours or days before a major rainstorm arrived
We know this because these dinosaurs left behind some of the best-preserved dinosaur mummies ever found, with clay molds that retain details such as skin, spines, and even the first hooves ever seen on a reptile.
These mummies belong to the species Edmontosaurus annectens, herbivorous, duck-billed dinosaurs that roamed North America, like ancient buffalo.
They are well-known to scientists because they are common and often found in good preservation.
Researchers from the University of Chicago led a study that closely examined several of these mummies found in a 10-kilometer region of Wyoming, USA, called the “mummy zone,” where preservation conditions are exceptionally good.
Surprising New Discoveries
Two newly discovered mummies have revealed features never before seen.
The first is a young animal, about two years old when it died.
This is the first large dinosaur found with its complete flesh profile, including a crest running along its neck and spine.
The second specimen is a young adult, between five and eight years old.
It still has a complete row of small spines along its back, from its hips to the tip of its tail.
Some of these spines had been found before, but never so complete.
The most intriguing find, however, are the hooves on its hind legs.
This discovery is rare: not only is it the first time hooves have been found on a dinosaur, but also on any reptile.
Furthermore, at between 66 and 69 million years old, these are some of the oldest hooves ever recorded on any animal.
Researchers believe hooves may have emerged even earlier, in the Jurassic period, in armored dinosaurs like stegosaurs and ankylosaurs, which had robust feet and left footprints with rounded toes.
How were these mummies formed?
To understand how these mummies were preserved, scientists used optical scans, X-rays, CT scans, and electron microscopes.
They found that there is no longer any organic material, such as skin or organs, nor any traces of internal structures.
Instead, all that remains is preserved as a thin layer of clay, less than 1 millimeter thick.
This clay formed when the material solidified over a layer of microbes that covered the bodies as they decomposed.
The Story Behind the Death
These finds tell the story of these dinosaurs’ deaths in stunning detail.
The wrinkled skin, which was very close to the bones, shows that the bodies were exposed to the hot sun for hours or days after death.
Drought has been confirmed as the cause of death for at least some of these dinosaurs.
What happened next is tragically ironic: soon after death, the bodies were quickly buried by a large amount of sediment, with mud and broken tree trunks in the same layer.
“These details show that the bodies were buried by a flood at or very close to the site of death, within a matter of hours or, at most, days,” the researchers explain.
They estimate that the time between death and burial of these mummies was about a week or a few weeks, within a single season.
Why is this important?
Most of what we know about dinosaurs comes from fossilized bones, but sometimes soft tissues, such as skin, feathers, scales, or even organs, survive.
These dinosaur mummies offer one of the clearest glimpses of these ancient animals, almost like time travel.
Published in 10/24/2025 01h23
Text adapted by AI (Grok) and translated via Google API in the English version. Images from public image libraries or credits in the caption. Information about DOI, author and institution can be found in the body of the article.
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