Dinosaur “mummies” couldn’t be further from my mind as I stomped through the grassy Zerbst Ranch in eastern Wyoming, and then students from the University of Chicago went on a field trip related to my “Dinosaur Science” course.
As a university professor, I realized early on that to understand paleontology, students would need to see firsthand where fossils are born. And that outdoor experience had to be real, a place where I wanted to be – a place we managed to discover.
I chose the outcrops of the Lance Formation, a rock formation consisting mostly of sandstones laid down during the last few million years of the dinosaur era. These rocks are well-lit in the dry lowlands of Wyoming, traversed by dinosaur hunters for more than a century. But maybe they missed something.
Then I saw.
At the top of the hill lay a mass of concrete—hardened, iron-stained rock the size of a compact car—surrounded by fragments of fossilized bones. A series of small stick-shaped bones jutted from its side, which I recognized as the abdominal ribs of a giant predator. Tyrannosaurus rex.
Mummies nearby
But T. rex was more than one among the wonderful finds that outdoor season. On the same field trip, colleagues working nearby discovered two fossilized duckbills, a herbivorous dinosaur that roamed in herds and grew to T. rex. They showed signs of exceptional preservation.
A vertebra—part of the spine—and some ossified tendons protruded from the vertical wall of the incision in the seasonally dry river.
“What do you think?” asked my colleague Marcus Eriksen, who counts paleoart, science education, and environmentalism as his other pillars alongside paleontology. “You’ve got the back of a duck,” I said, referring to it Edmontosaurus annectensthe official name of the dinosaur that most likely is T. rexdinner menu.
It would take Marcus two outdoor seasons to remove the 15 feet of rock covering the skeleton. To his surprise, the tailbones were covered in large areas of scaly skin, with a row of spikes at the top. When I visited the exposed skeleton and looked at his feet, I saw a line of hair around the terminal bone of the toe. “Back off, take more,” I said wide eyed at what I saw. “I think it has hooves.”
Yet another group of bone hunters in the area found a Triceratops skeleton next to a large slab of his scaly skin. Finding even a patch of skin on a skeleton deserves celebration in paleontological circles. Discovering large areas of the outer surface of a fleshy dinosaur is the discovery of a lifetime.
The secret of mummification
How is dinosaur “mummy” skin preserved? What constitutes “skin impressions”?
Are these dinosaur “mummies” preserved like human mummies from Egypt, where after someone died, salt and oils were applied to the skin, hair, internal organs and, as recently shown, to dry and preserve their genome?
No. Dinosaur “mummies” do not preserve dry skin. However, many researchers believed that perhaps traces of tissue structure or even original organic matter might remain.
In order to lift the veil on dinosaur mummification, I needed not only my knowledge, but also knowledge and digital knowledge. I recruited Evan Saitta to pinpoint the composition of ancient scaly skin after learning that he was making reptilian skin to simulate fossilization.
I brought others on board: Dan Vidal, a Spanish paleontologist with the ability to digitally capture surface detail in 3D; Nathan Myhrvold, a polyglot scientist fresh out of steak chemistry; Stephanie Baumgart, a paleontologist who studies CT scans of living vertebrates; María Ciudad Real and Lauren Bop, the former skilled in analyzing CTs and the latter in combining them into composite figures; Tyler Keillor, who would invent new methods for cleaning ancient leather fabric; and Dani Navarro, the great Spanish paleoartist reimagining prehistoric scenes.
Clay mask, crests, hooves and scales
We used a diamond blade to cut the skin, spikes, and hooves, and found that they were all made of a very thin confining layer of clay—a clay mask or template—one-hundredth of an inch (less than 1 millimeter) thick. The sand on either side of the clay layer did not differ, indicating that when the framework was buried, the same sand that pressed outwards entered through the many cracks and holes into the dry, hollow framework, filling all the interior spaces. Even the spaces inside the spikes and hooves were filled with sand.
We found no evidence of tissue structures within the clay layer, whether looking at calluses, spikes, or hoofs. And we couldn’t find any traces of original organic matter. In other words, the original skin in the clay layer must have decomposed and washed away, and the same groundwater saturated the bones on their way to fossilization.
Our duck’s very realistic looking skin, spikes and hooves are actually a clay mask, a thin layer applied to the outside that captures all the original shape and texture of the fleshy body surface.
To test the digital image we created, we compared a digital version of the duck’s hoof foot to a fossilized duck footprint on the Canadian Museum shelf found in beds of the same age as the Lance Formation. We adjusted the foot size a bit to see if it fits perfectly. Together, the foot and footprint created the first complete image of a fleshy duck foot.
The only duckling alive at that time was Edmontosaurus annectenslikely track maker. The footprint was preserved so perfectly that you could see the scales on the sole of the foot.
“Mummy” zone
Due to the unique geology of the Lance Formation, many of these dinosaur mummies have been preserved under clay in a small area.
Drilling for natural gas and oil in Wyoming has shown that the sandstone rock that makes up the Lance Formation is very deep beneath the mummies, more than 1,000 meters (more than 3,200 feet) deep. It is five times thicker than anywhere else in the West, suggesting that the formation subsided more rapidly in the Mummy Zone, with periodic floods covering the desiccated dinosaur carcasses.
During this last era of the dinosaurs, a monsoon climate prevailed in western North America. Severe droughts have brought death to vast herds of duck-billed dinosaurs, some of which sought the last of their water in dry riverbeds before succumbing. Flash floods followed, bringing tons of sandy sediment that would instantly cover the sun-dried dinosaur carcass.
Only in rare cases do scientists have the opportunity to accurately imagine what a large dinosaur looked like alive, because we usually only have bones to reconstruct beasts that have no close living analogue. Dinosaur “mummies” provide us with that extraordinary opportunity for preservation.
My dream team of researchers has been able to clean, scan, resize, resize, reassemble, and otherwise recreate life-like anti-beak dinosaurs from rare dinosaur mummies – breathing life into fossils and allowing everyone to appreciate the grandeur of a past life.
This article is republished from The Conversation, a not-for-profit independent news organization that provides facts and sound analysis to help make sense of our complex world. It was written by: Paul C. Sereno, University of Chicago
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Paul C. Sereno is president of the Scitopia Foundation, a 501c3 non-school science education organization with operations and founding planning facilities in Chicago (Scitopia Chicago).