Wyoming’s ‘Mummy Zone’ Unlocks Deep Secrets: The Hoofed Edmontosaurus Redefines Dinosaur Biology

Paleontologists have uncovered ‘mummified’ Edmontosaurus specimens in Wyoming, showcasing remarkable soft tissue preservation including the first-ever documented hooves on a land vertebrate dinosaur, alongside crests and scales, thanks to a unique ‘clay templating’ preservation process.

For decades, our understanding of how dinosaurs truly appeared in life has largely been pieced together from skeletal remains. Soft tissues like skin, muscle, and internal organs rarely fossilize, leaving much to scientific inference. However, a groundbreaking discovery in the badlands of Wyoming is challenging these long-held assumptions, providing an unprecedented, fleshed-out view of a large dinosaur: the duck-billed Edmontosaurus annectens.

The ‘Mummy Zone’: A Rare Glimpse into the Past

Researchers from the University of Chicago, led by senior author Paul Sereno, have unearthed two exceptionally preserved Edmontosaurus specimens. These fossils, though dubbed “mummies,” are not like the human-prepared mummies of ancient Egypt where organic material remains. Instead, they are incredible examples of “clay templating,” where the external fleshy surface of the dinosaur was preserved as a sub-millimeter thin clay mask over the fossilized skeleton. This unique preservation occurred approximately 66 million years ago, just before the asteroid impact that ended the age of dinosaurs.

Sereno’s team utilized historical photographs and field investigation to relocate sites in east-central Wyoming where similar dinosaur “mummies” were discovered in the early 20th century. This area, which they’ve dubbed a “mummy zone,” has yielded significant finds:

• “Ed Jr.”: A late juvenile, estimated to be about 2 years old at its time of death.
• “Ed Sr.”: An early adult, approximately 5 to 8 years old when it perished.

These two specimens provide continuous areas of preserved external skin surface, offering the most comprehensive understanding of a large dinosaur’s appearance to date, as detailed in their findings published in the journal Science.

Unveiling the True Appearance: Crests, Spikes, and Scales

Using an array of advanced imaging techniques, including x-rays, micro-CT scans, 3D surface imaging, and clay analyses, the scientists meticulously reconstructed the Edmontosaurus’s soft anatomy. The findings painted a vivid picture of these duck-billed giants:

• A distinct, fleshy crest ran along the neck and trunk, transitioning into a single row of spikes over the hips and down the tail, with each spike positioned directly over a vertebra.
• The dinosaur’s lower body and tail were covered in tiny, pebble-like scales, surprisingly small (1–4 millimeters) for an animal that could grow over 40 feet (12 meters) long.
• Wrinkles observed over the rib cage suggest the skin was relatively thin.

This level of detail offers a complete profile, moving beyond scattered patches of skin that had been the norm for paleontological reconstructions. It’s truly “the first time we’ve had a complete, fleshed-out view of a large dinosaur that we can really feel confident about,” noted Paul Sereno in a statement by the University of Chicago News.

The Unexpected Revelation: Hooves on a Dinosaur

Perhaps the most astonishing discovery was the presence of hooves on the feet of the larger Edmontosaurus mummy. The tip of each of its three hind toes was encased in a wedge-shaped hoof with a flat bottom, strikingly similar to those found on modern horses.

This finding marks several “firsts” in vertebrate paleontology:

• The earliest hooves documented in a land vertebrate.
• The first confirmed hoofed reptile.
• The first hoofed four-legged animal with different forelimb and hindlimb posture.

The team combined CT scans of the mummy’s feet with 3D images of well-preserved duck-billed dinosaur footprints to accurately reconstruct the hind foot. Unlike the forefeet, which touched the ground primarily with their hooves, the hind feet featured a fleshy heel pad behind the hooves, suggesting adaptations for different types of locomotion. The researchers suggest these hooves would have been vital for efficiently moving through muddy terrains or running on hard ground, a function reminiscent of modern hoofed mammals.

Convergent Evolution at Play

The presence of hooves in Edmontosaurus is a prime example of convergent evolution—a phenomenon where unrelated species independently evolve similar traits to adapt to similar environments or ecological niches. While mammals like horses and cows developed hooves millions of years later, the Edmontosaurus evolved them much earlier, demonstrating that similar environmental pressures can lead to similar biological solutions across vastly different lineages.

The Mechanism of ‘Clay Templating’ Preservation

The extraordinary preservation of these specimens puzzled scientists, leading to a detailed investigation into the “clay templating” process. The team’s research suggests the following sequence of events:

1. The dinosaurs likely perished during a drought, leading to their carcasses becoming desiccated and dried out in the sun.
2. A sudden flash flood then covered the dried bodies, immersing them in wet sediment.
3. A biofilm on the carcass surface reacted with the wet sediment, electrostatically pulling clay particles out of it.
4. This clay congealed into a wafer-thin template layer, capturing the precise three-dimensional contours of the external surface.
5. Over longer timescales, the original organic material slowly decayed, while the skeleton below fossilized, leaving behind the clay mask as an imprint.

This fluke event of preservation provides an invaluable “mask” or “template” of dinosaur soft anatomy that traditional fossilization rarely allows.

Edmontosaurus: A Key Player in the Late Cretaceous Ecosystem

Living at the very end of the Cretaceous period (145 million to 66 million years ago), Edmontosaurus was a dominant herbivore across western North America. It shared its environment with other iconic dinosaurs such as the formidable Tyrannosaurus rex and the horned Triceratops. Growing to lengths exceeding 40 feet, Edmontosaurus was often referred to as the “cow of its day,” forming large herds and serving as a frequent prey item for apex predators like T. rex. Interestingly, during their field work in the “mummy zone,” researchers also found fossils of Tyrannosaurus and Triceratops, with preliminary observations suggesting the possibility of feathered T. rex specimens—a topic that promises further revolutionary insights.

Shaping the Future of Paleontology and Public Understanding

Beyond the anatomical revelations, this study offers a comprehensive toolkit for future research into dinosaur soft anatomy. It provides:

• New preparation methods for delicate clay template fossils.
• A clear lexicon for describing soft structures and scales.
• A detailed imaging workflow from raw fossil to a complete flesh model.
• A “recipe” for understanding how dinosaur mummification through clay templating occurred.

The discoveries encourage targeted searches for similarly preserved specimens in the Wyoming strata and beyond, promise more accurate biomechanical models, and invite further analyses into the conditions under which clay templating takes hold. For the fan community, these findings transform how we visualize dinosaurs, bringing them closer to real animals with intricate skin textures, specialized foot structures, and dynamic body features, challenging simplified depictions and sparking new imaginings of prehistoric life.