In a groundbreaking study published in Science, researchers from the University of Chicago have unveiled the extraordinary process that preserved the remains of a duck-billed dinosaur, Edmontosaurus annectens, dating back 66 million years. This process, known as clay templating, has resulted in dinosaur “mummies” that capture intricate details of scales and hooves, providing an unprecedented view of these ancient creatures.
The research team, led by Dr. Paul Sereno, Professor of Organismal Biology and Anatomy at UChicago, utilized advanced imaging techniques to reconstruct the dinosaur’s appearance, revealing features such as a tall crest over the neck and trunk and a row of spikes along the tail. “It’s the first time we’ve had a complete, fleshed-out view of a large dinosaur that we can really feel confident about,” Sereno stated. The findings were made in Wyoming’s unique “mummy zone,” a site rich with potential for further discoveries.
From Field Puzzle to Full Profile
The journey to this discovery began with Sereno and his team revisiting sites in east-central Wyoming, where several notable dinosaur mummies were unearthed in the early 20th century. By mapping out this compact “mummy zone,” the researchers excavated two new Edmontosaurus mummies, one a late juvenile and the other an early adult, both exhibiting extensive preserved skin surfaces.
Unlike human-prepared mummies, these dinosaur mummies retain no organic material. Instead, the preservation occurred through a sub-millimeter clay film that formed on the carcass surface shortly after burial. “This is a mask, a template, a clay layer so thin you could blow it away,” Sereno explained. The preservation was a result of a unique electrostatic attraction of clay to the carcass surface, following a rapid burial by a flash flood.
Imaging Techniques and Reconstruction
To achieve these insights, the team employed a variety of imaging tools, including hospital and micro-CT scans, X-ray spectroscopy, and clay analyses. These methods revealed how the preservation process unfolded, allowing the researchers to reconstruct the dinosaur’s appearance in life. Fossil Lab manager Tyler Keillor led the meticulous cleaning process, while postdoctoral scholar Evan Saitta and others used 3D imaging to further explore the anatomy and movement of the duckbill.
“I believe it’s worth taking the time to assemble a dream team in order to generate science that can be appreciated by the general public,” Sereno said. “We’ve never been able to look at the appearance of a large prehistoric reptile like this — and just in time for Halloween.”
Crests, Spikes, and Scales
The researchers’ work with the two new mummies allowed them to reconstruct a comprehensive profile of Edmontosaurus annectens. “The two specimens complemented each other beautifully,” Sereno noted. The team identified a continuous midline feature, beginning as a fleshy crest along the neck and trunk, transitioning into a single row of spikes down the tail.
The lower body and tail featured large polygonal scales, while most of the skin was covered in small pebble-like scales. Wrinkles over the ribcage suggested a thin skin, providing further insights into the dinosaur’s physical characteristics.
A Hoofed Dinosaur
One of the most surprising discoveries was the presence of hooves on the hind feet of the larger mummy. Each of the three hind toes was encased in a wedge-shaped hoof with a flat bottom, similar to a horse’s. The team used CT scans and 3D images to fit these hooves into a footprint from the same period, accurately reconstructing the hind foot’s appearance. This discovery marks the first documented hooves in a land vertebrate and the first confirmed hooved reptile.
“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.
Shaping the Future of Paleontology
Beyond the anatomical revelations, this study provides a toolkit for future research on dinosaur soft anatomy. It introduces new preparation methods, a clear lexicon for soft structures, and an imaging workflow from fossil to flesh model. The team’s research offers a new model for dinosaur mummification involving clay templating, which can be applied to future finds.
The authors anticipate further discoveries, suggesting targeted searches for similarly preserved specimens in Wyoming and elsewhere. They also propose biomechanical models that now have reliable external boundaries and analyses to determine when and where clay templating occurs.
“This may be the single best paper I’ve released,” Sereno remarked. “From field to lab to 3D reconstructions along with a suite of useful terms defined, it’s a tour de force, and it tells a coherent story about how these remarkable fossils come to be and what we can learn from them.”
The study not only enriches our understanding of dinosaur biology but also sets a new standard for paleontological research, promising exciting developments in the field.
