Rare Dinosaur ‘Mummies’ Show Their Features as We’ve Never Seen Them Before

In the badlands of Wyoming lies the “mummy zone.” This section of rocks dating back to the Cretaceous Period has produced several strikingly well-preserved dinosaur specimens over the last century, and now, scientists have used two of them to definitively determine what one long-lost species looked like.

In the early 2000s, researchers found two specimens of Edmontosaurus annectens, a large duck-billed dinosaur, in the mummy zone. The fossils were remarkably preserved, still showing fine details of scales and hooves 66 million years after these animals walked the Earth. In a study published Thursday in the journal Science, the team used these fossils to reveal exactly how this happened and reconstruct the species’ living appearance.

“It’s the first time we’ve had a complete, fleshed-out view of a large dinosaur that we can really feel confident about,” co-author Paul Sereno, a professor of organismal biology and anatomy at the University of Chicago, said in a release.

The preservation power of clay templating

In the early 1900s, researchers found several exceptionally well-preserved dinosaur fossils in a particular section of the Lance Formation—a division of rocks in east-central Wyoming dating back to the Cretaceous Period. Decades later, Serrano and his colleagues used historical photos and field sleuthing to map the area, dubbing it the “mummy zone.”

In 2000 and 2001, they excavated two E. annectens mummies—a late juvenile and an early adult—with large portions of their external skin surface still preserved. Unlike human mummies found in Egyptian tombs, however, the skin, spikes, and hooves of these dino mummies were preserved not as tissue but as an extremely thin clay film that formed on the carcass.

“This is a mask, a template, a clay layer so thin you could blow it away,” Sereno explained. “It was attracted to the outside of the carcass in a fluke event of preservation.”

Using a variety of imaging techniques and observations of the discovery site, he and his team figured out exactly how this preservation process—called clay templating—occurred. Soon after these two dinosaurs perished, a flash flood struck, burying their bodies in sediment.

The decaying carcasses were coated in a film of bacteria, which electrostatically attracted clay found in the sediment. This covered the bodies in a clay mask no more than 0.01 inches (0.02 centimeters) thick, creating a 3D cast of their true surface. The organic material decayed away, and over millions of years, the skeleton beneath the cast fossilized.

Bringing a long-lost dinosaur to life

The two E. annectens mummies allowed the researchers to reconstruct the species’ living appearance, determining that it had a fleshy crest along its neck and back that turned into a single row of tail spikes. Its thin skin was mostly covered with small pebble-like scales. Most surprisingly, the hind feet of the adult mummy bore wedge-shaped hooves.

“There are so many amazing ‘firsts’ preserved in these duck-billed mummies—the earliest hooves documented in a land vertebrate, the first confirmed hooved reptile, and the first hooved four-legged animal with different forelimb and hindlimb posture,” Sereno said.

Digital artists used these insights to recreate the appearance and movement of the duckbill walking on soft mud near the end of the Cretaceous Period.

This work “tells a coherent story about how these remarkable fossils come to be and what we can learn from them,” Sereno said. As researchers continue to explore the mummy zone, there’s no telling what new discoveries await them.