For over a century, the remarkably preserved ‘skin’ on duck-billed dinosaur ‘mummies’ from Wyoming puzzled paleontologists. New research reveals these aren’t fossilized flesh at all, but incredibly detailed clay molds formed by microbes during decay, offering an unprecedented, lifelike glimpse into these ancient giants, complete with spikes and the earliest known hooves in a reptile.
More than a century ago, the discovery of what appeared to be dinosaur mummies captivated the scientific world. Prolific fossil collector Charles Sternberg unearthed the skeleton of a duck-billed Edmontosaurus dinosaur in eastern Wyoming, notably covered in what was believed to be fossilized flesh and skin. This groundbreaking find, followed by another just kilometers away, marked the first “dinosaur mummies” ever recorded and initiated a perplexing scientific mystery.
These extraordinary specimens, with their apparent preservation of soft tissues like skin, spikes, and even hooves, challenged conventional paleontological wisdom. Typically, soft tissues require highly specific, oxygen-starved environments for preservation, such as lagoons or seabeds. Yet, these Wyoming mummies were found in coarse, oxygenated river deposits—an environment where such preservation was thought to be nearly impossible. This contradiction left paleontologists baffled for generations, a mystery that has finally been unraveled.
A Century of Misconception: Unraveling the ‘Mummy’ Myth
New research, led by University of Chicago paleontologist Paul Sereno, has dramatically altered our understanding of these famous fossils. Published in the journal Science, the study reveals that the exceptionally preserved features aren’t fossilized flesh but rather intricate clay molds. These delicate, approximately 1-millimeter-thick formations were crafted by microorganisms during the early stages of the creatures’ decay.
“That’s going to come as a shocker to a lot of people,” remarked Sereno, acknowledging the profound shift in perspective this discovery brings. The process of clay molding was previously known to preserve soft-bodied animals in oxygen-poor aquatic environments. However, no one imagined it could “work its magic on a dinosaur buried suddenly by sand in a flooded river,” an environment traditionally considered hostile to such preservation, as reported by Scientific American.
The Magic of Clay Templating: How Microbes Sculpted Dinosaur Features
The secret to this stunning preservation lies in a process Sereno and his team call clay templating. It begins with the dinosaur carcass undergoing desiccation during a drought. When suddenly engulfed by sediment, likely from a flash flood, a thin layer of bacteria would form a biofilm on the wet, porous surface. This biofilm then electrostatically attracted surrounding clay minerals. Weeks after burial, the actual organic soft tissues decayed and were washed away by groundwater, leaving the thin clay mask to permanently capture the three-dimensional form of the dinosaur’s exterior.
This clay mask, sometimes no thicker than a human hair, functioned like a natural mold. It captured the intricate details of the animal’s skin, crest, and even wrinkles with astonishing fidelity. The organic material vanished over millions of years, but the delicate clay film remained, providing an exact imprint of the dinosaur’s external features, offering an unprecedented, lifelike reconstruction of a large dinosaur.
New Discoveries from the ‘Mummy Zone’
As part of their investigation, Sereno’s team played detectives, using historical documents to pinpoint and relocate the original discovery sites in east-central Wyoming. This endeavor led to the discovery of even more ‘mummies’ within a 10-kilometer diameter, an area Sereno now refers to as the “mummy zone.” Among these new finds were two more Edmontosaurus annectens specimens: an adult (dubbed “Ed Sr.”) and, remarkably, a juvenile (“Ed Jr.”) of the same species.
The juvenile, Ed Jr., estimated to be around two years old at its time of death, represents the first subadult dinosaur ‘mummy’ ever found. It also holds the distinction of being the first large-bodied dinosaur with a fully preserved fleshy outline, including its neck and trunk. Ed Sr., an early adult, revealed additional complex soft tissues beyond scales. These included rows of spikes, similar to those seen on modern lizards, running along its neck and back, continuing over its hips and tail.
The Revelation of Hooves: A First for Reptiles
Perhaps the most astonishing discovery involved Ed Sr.’s feet: the first known hooves ever found in a reptile. Using advanced micro-CT scans, the researchers observed that each of the three toes on the dinosaur’s hind feet was encased in a wedge-shaped hoof with a flat bottom—strikingly similar to those of a horse. These hooves would have provided crucial stability and support for the dinosaur’s massive body as it navigated soft ground.
The team even managed to fit the reconstructed feet perfectly into a fossilized footprint found at the same site, confirming their findings with remarkable precision. “There are so many incredible firsts here,” Sereno stated. “This is the earliest evidence of hooves in any land vertebrate—and the first time we’ve seen a reptile with hooves at all.” This adds another layer of complexity to our understanding of dinosaur anatomy and locomotion.
Reshaping Paleontology: A New Era for Dinosaur Understanding
The implications of this study are far-reaching. It not only redefines what scientists mean by “dinosaur mummies”—shifting from preserved flesh to intricate clay molds—but also broadens the range of known depositional settings in which soft tissues can be preserved. This knowledge is invaluable, as it provides a framework for how similar fossils might form in the future and guides paleontologists on what specific conditions to look for in their ongoing hunt for more dinosaur mummies.
The meticulous examination involved modern tools such as micro-CT scans, x-ray spectroscopy, and 3D surface imaging. Fossil lab manager Tyler Keillor led the painstaking process of exposing the fragile clay layer, which was so thin it could be blown away with a breath, highlighting the incredible delicacy of these unique fossils.
Sereno expressed deep satisfaction with the work, calling it “the single best paper I’ve ever released.” He emphasized how it successfully integrates fieldwork, lab science, and digital reconstruction to tell a complete story: from how these fossils formed, to what they reveal, and how they will “change the way we see dinosaurs forever.” The new understanding provides the most confident glimpse yet of what these magnificent giants truly looked like when they roamed the Earth 66 million years ago, painted vividly through the artwork of Dani Navarro, showing a scaly, hoofed giant with a crest and spikes, traversing ancient river mud.
