In a new paper in Science, experts from the University of Chicago describe steps that took place some 66 million years ago to transform carcasses of a duck-billed dinosaur, Edmontosaurus annectens, into dinosaur “mummies” preserving fine details of scales and hooves.
Called clay templating, the external fleshy surface of the dinosaur was preserved over the skeleton after 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 fleshy appearance of the animal in life, from a tall crest over the neck and trunk to a spike row over its tail and hooves sheathing its toes. Combined with fossilized footprints, the appearance of a duck-billed dinosaur—long guessed at but never demonstrated in this detail—is now at hand.
“It’s the first time we’ve had a complete, fleshed-out view of a large dinosaur that we can really feel confident about,” said senior author Paul Sereno, professor of organismal biology and anatomy at UChicago. “The badlands in Wyoming where the finds were made is a unique ‘mummy zone’ that has more surprises in store from fossils collected over years of visits by teams of University undergrads.”
From field puzzle to full profile
Using historical photos and field sleuthing, Sereno and his team relocated the sites in east-central Wyoming where several famous dinosaur mummies were discovered in the early 20th century, mapping out a compact “mummy zone.” In those stacked river sands, they excavated two new Edmontosaurus mummies—a late juvenile and an early adult—with large continuous areas of preserved external skin surface.
Sereno is quick to explain that his dinosaur mummies are not like the human-prepared mummies in Egyptian tombs; no organic material remains. Across both newly described specimens and previous ones labeled mummies (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 carcass surface soon after burial.
“This is a mask, a template, a clay layer so thin you could blow it away,” Sereno said. “It was attracted to the outside of the carcass in a fluke event of preservation.”
Learn how the duck-billed dinosaur Edmontosaurus annectens was preserved in the “mummy zone” of Wyoming. (Video courtesy of UChicago Fossil Lab)
The team used several imaging tools, including hospital and micro-CT scans, thin sections, X-ray spectroscopy, clay analyses and examination of the discovery site—all of which pointed to how this unique preservation occurred. After each sun-dried dinosaur carcass was covered up suddenly in a flash flood, a biofilm on the carcass surface electrostatically pulled clay out of the wet sediment to congeal a wafer-thin template layer, capturing the true surface in three dimensions, after which the organic material decayed away and the skeleton below fossilized over longer timescales.
Exposing such a soft, paper-thin clay boundary required hours of careful cleaning led by Fossil Lab manager Tyler Keillor, a co-author of the paper. Other researchers led by postdoctoral scholar Evan Saitta used 3D surface imaging, CT scans and contemporary footprints to follow the soft anatomy, characterize the sediment inside and outside the mummy and fit the hooves back into a footprint. Digital artists then joined the science team to reconstruct the fleshy appearance and movement of the duckbill, walking on soft mud near the very end of the dinosaur era.
