Dinosaur ‘mummies’ unlock the secret to their real-life appearance

In a new paper ScienceUniversity of Chicago experts describe the steps that took place about 66 million years ago to turn the carcass of Edmontosaurus aniketons, a duck-billed dinosaur, into a dinosaur “mummy,” preserving fine details of scales and hooves.

Called templating clay, the outer fleshy surface of the dinosaur was preserved over the skeleton after its burial by a thin clay mask no more than 1/100th of an inch thick. Using an array of imaging techniques, the scientists reconstructed the animal’s fleshy appearance in life, from a long ridge on its neck and trunk to a row of spikes atop its tail and the ridges that criss-cross its toes. Combined with fossilized footprints, the appearance of a duck-billed dinosaur—long speculated but never demonstrated in this detail—is now in his hands.

“This is the first time we have a complete, symmetrical view of a large dinosaur that we can feel really confident about,” said senior author Paul Sereno, PhD, professor of paleontology and anatomy at UCLA. “The Badlands in Wyoming where it was found is a unique ‘mummy zone’ with more surprises in store than fossils collected during years of visits by teams of university undergrads.”

From a field puzzle to a complete profile

Using historical photographs and field plotting, Sereno and his team relocated sites in east-central Wyoming where several famous dinosaur mummies were discovered in the early 20th century, creating a compact “mummy zone” map. In these stacked river sands, they excavated two new Edmontosaurus mummies — a late juvenile and an early adult — with large continuous areas of preserved outer skin.

Sereno is quick to point out that his dinosaur mummies are not the same as the human-dressed mummies in Egyptian tombs. No organic material remains. In both the newly described specimens and the labeled mummies of previous people (including those found at the same site in the 20th century), the skin, spikes and hooves were preserved not as tissue, but as a sub-millimeter clay film that formed on the surface of the corpse shortly after burial.

“It’s a mask, a template, a layer of clay that you can blow off,” Sereno said. “It was attracted to the outside of the carcass in a fluke event of conservation.”

The team used several imaging tools, including hospital and microCT scans, thin sections, X-ray spectroscopy, soil analyses, and examination of the discovery site, all of which revealed how this unique preservation occurred. After each sun-dried dinosaur carcass was suddenly covered in a flash flood, a biofilm on the surface of the carcass electrostatically extracted clay from the wet sediment to form a wafer-thin template layer, which then drew the true surface in three dimensions, after which the bottom of the organic matter and the skeleton were removed from the foam.

Exposing the confines of such soft, paper-thin soil required hours of careful cleaning led by Fossil Lab Manager Tyler Keller, who co-authored the paper. Other researchers, led by postdoctoral scholar Evan Sita, used 3D surface imaging, CT scans, and contemporary footprints to follow the soft anatomy, characterize sediments inside and outside the mother, and fit the hooves into the footprint. Digital artists then joined the science team to recreate the duckbill’s fleshy appearance and movements, walking on soft mud at the very end of the dinosaur era.

“I believe it’s worth taking the time to assemble a dream team to produce science that can be appreciated by the general public,” Sereno said. “We’ve never seen the appearance of such a large prehistoric reptile — and just in time for Halloween.”

Crusts, spikes and scales

Working with two new mummies, the researchers reconstructed a complete, fleshy profile of Edmontosaurus aniketons.

“The two paradigms complemented each other beautifully,” Sereno said. “For the first time, we can see the whole profile instead of scattered patches.”

They identified a continuous midline feature that began as a fleshy crest along the neck and trunk and transitioned to a single row of spikes running down the tail above the hips.

The lower body and tail had the largest polygonal scales, although most of the smaller pebble-like scales were only 1–4 mm across, surprisingly for a dinosaur growing to over 40 feet in length. Wrinkles preserved on the ribcage suggest that this duck had thin skin.

A hoofed dinosaur

The big mummy’s hind feet hold the biggest surprise: hooves. The tip of each of the three hind toes was encased in a wedge-shaped hoof shaped like a horse. The team used CT scans of the mummy’s foot and 3D images of the best-preserved duckbill impression from the same time, fitting the former into the latter. Using information from both sources, they accurately reconstructed the appearance of the hindfoot. Unlike a toe that only touches the ground with its hooves, the hindfoot has a fleshy heel pad behind the hooves.

“These duck-blood mummies preserve a number of amazing ‘firsts.’

Shaping the future of the field

Beyond the anatomical revelations, the study offers a toolkit for future research into dinosaur soft anatomy: new preparation methods, a clear glossary for soft structures and scales, an imaging workflow from fossil to body model, and a recipe for producing dinosaur mummies. More than standalone discoveries, the team’s mummy research offers a new model for dinosaur mummification that involves clay templating that can be tested on future finds.

The authors also point to what comes next: targeted searches for similar Wyoming strata and similar preserved specimens elsewhere. Biomechanical models that now have reliable external limits. And companion analyzes investigate when and where clay templating takes place.

“This may be the single best paper I’ve ever released,” Sereno said. “With 3D reconstructions from the field to the lab, along with a suite of useful terminology, it’s a tour de force, and it tells a coherent story of how these remarkable fossils came to be and what we can learn from them.”