If you happened upon the Wyoming badlands 66 million years ago, you might have noticed something unusual: the sun-baked remains of a duck-billed dinosaur, its scales shimmering in the fading light, soon to be engulfed by swift floodwaters. That image, preserved in an extraordinary manner, has finally disclosed the true form of one of the most prevalent creatures from the age of dinosaurs.
Paleontologists from the University of Chicago have released a comprehensive reconstruction of Edmontosaurus annectens in the journal Science, utilizing two exceedingly well-preserved specimens that display external anatomy with remarkable accuracy. These fossils, referred to as dinosaur “mummies” despite lacking any original organic matter, reveal what researchers have long speculated: how these colossal herbivores appeared when alive.
The key lies in clay, specifically an exceedingly thin layer measuring no more than 1/100th of an inch that adhered to the dinosaur’s skin post-burial. This “clay templating” technique created a three-dimensional mold of the creature’s outer layer, preserving details down to individual scales and the precise form of its hooves.
Discovering the Mummy Zone
Paul Sereno, who spearheaded the research team, characterizes the discovery site as a compact “mummy zone” located in east-central Wyoming where several renowned dinosaur mummies were unearthed in the early 20th century. By employing historical photographs and meticulous detective work, his team re-located these sites and excavated two new specimens: a late juvenile and an early adult.
The preservation phenomenon resembles a perfect storm of geological conditions. After each carcass dried in sunlight, sudden flash floods buried it. A biofilm on the surface electrostatically drew clay particles from the surrounding wet sediment, forming an ultra-thin template layer that captured the accurate contours of the skin. Subsequently, the organic material decayed, leaving a clay impression draped over the fossilizing skeleton.
“This is a mask, a template, a clay layer so thin you could blow it away. It was drawn to the exterior of the carcass in a rare preservation event.”
Tyler Keillor, the Fossil Lab manager who meticulously cleaned the specimens, spent hours revealing the fragile clay boundary without damaging it. The team then employed a range of imaging technologies: hospital CT scans, micro-CT scans, X-ray spectroscopy, and clay analyses to interpret their findings.
Crests, Spikes, and Surprising Hooves
The two specimens complemented one another flawlessly, showcasing a complete profile from head to tail. A fleshy crest extended along the neck and torso, transitioning at the hips into a singular row of spikes marching down the tail. Each spike was aligned directly over a vertebra, interconnected in sequence.
The scales themselves were surprisingly small, most measuring merely 1 to 4 millimeters across, even as the creature grew to over 40 feet in length. Larger polygonal scales adorned the lower body and tail. Preserved wrinkles over the ribcage suggest the skin was relatively thin, potentially more susceptible than scientists previously believed.
However, the most astonishing revelation came from the hind feet. The larger mummy exhibited something no one anticipated: true hooves. Each of the three hind toes terminated in a wedge-shaped hoof with a flat base remarkably akin to a horse’s hoof. The forefeet also had hooves but contacted the ground differently, while the hind feet featured a fleshy heel pad situated behind the hooves.
“There are numerous astonishing ‘firsts’ preserved in these duck-billed mummies: the earliest hooves recorded in a terrestrial vertebrate, the first confirmed hooved reptile, and the first hooved quadruped with differing forelimb and hindlimb posture.”
The team advanced even further, correlating the mummy’s feet to fossilized footprints from the same epoch. By utilizing CT scans and 3D imaging, they perfectly fitted the reconstructed foot into ancient tracks, validating their anatomical interpretation.
Sereno regards it as potentially his finest published research, a stellar accomplishment that transitions from fieldwork through laboratory preparation to the final 3D reconstruction. The study equips future researchers with a comprehensive toolkit: preparation techniques, standardized terminology for soft structures, a workflow for imaging, and a testable model for how clay templating produces dinosaur mummies.
The Wyoming badlands, Sereno observes, likely conceal more revelations. Years of excavation by university undergraduates have amassed a collection awaiting analysis. And now, other paleontologists possess a clear preservation mechanism to apply to their own discoveries, potentially unlocking similar details from dinosaurs around the globe.
[Science: doi.org/10.1126/science.adw3536]
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