Lead
In a revisit of the site where C.H. Sternberg first unearthed an Edmontosaurus in 1908, a University of Chicago–led team led by Paul C. Sereno recovered two exquisitely preserved Edmontosaurus annectens “mummies” in east-central Wyoming. The discoveries, published in Science (2025; DOI: 10.1126/science.adw3536), preserve sub-millimeter clay masks of skin and soft tissues and provide new details about crest shape, scale size, tail spikes and surprisingly hoof-like toes. The fossils come from a dense fossil pocket within the Lance Formation and were analyzed with CT, X-ray and photogrammetry to reconstruct life appearance more precisely than earlier restorations. Results revise century-old reconstructions and reveal anatomical features — including distinct fore- and hind-hooves — with implications for locomotion and evolution.
Key Takeaways
- Two new Edmontosaurus annectens mummies were recovered in the same Wyoming locality first worked by C.H. Sternberg in 1908; the findings are reported in Science, 2025 (DOI: 10.1126/science.adw3536).
- Soft-tissue “clay templating” produced masks under 1 millimeter thick that preserve skin texture, wrinkles, and the arrangement of crest and tail spikes.
- Most scales measure 1–4 millimeters across, rarely exceeding 1 centimeter toward the lower tail, indicating extremely fine, thin skin for an animal the size of an elephant.
- The dorsal crest transitions posteriorly into a row of spike-like structures aligned one-to-one with vertebrae, reconciling earlier, competing reconstructions by Knight (1909) and Horner (1984).
- Forelimbs bore a single central, hoof-like structure with a triangular “frog,” while hind feet had three wedge-shaped hooves plus a fleshy heel—morphologies analogous to modern equids and rhinos respectively.
- Geologic context: the fossils are in the Lance Formation, which averages ~200 meters thick but reaches ~1,000 meters in the mummy zone, suggesting unusually high local sedimentation.
- Additional mummies (a T. rex and a Triceratops) were recovered in the same area and are under study; preliminary observations suggest different taphonomic histories and skin architectures between taxa.
Background
Edmontosaurus annectens, a large hadrosaurid (duck-billed dinosaur) from the last few million years of the Cretaceous, entered scientific awareness after a partial, scaly specimen collected by C.H. Sternberg in 1908 and later displayed at the American Museum of Natural History. Early restorations, most famously by Charles R. Knight in 1909, reconstructed a fleshy crest extending along the back, but those images were informed by incomplete material and considerable artistic interpolation. In 1984 Jack Horner reported tail material with spike-like projections and proposed a different dorsal profile, sparking decades of competing reconstructions.
The new work retraces Sternberg’s field notes and local oral histories to relocate the “mummy zone,” a fossil-rich pocket under ten kilometers across in east-central Wyoming. The site sits within the Lance Formation, a transregional unit spanning parts of the northern Great Plains; at the mummy zone the formation shows anomalously thick accretion, which the team links to elevated sedimentation likely driven by frequent flooding. These taphonomic conditions enabled rare clay templating — a process long recognized for preserving soft-bodied deep-sea organisms but previously underappreciated for large terrestrial vertebrates.
Main Event
Sereno’s team returned to the historic area and, with painstaking archival work and interviews with local landowners, relocated concentrated fossiliferous exposures. Excavations yielded two Edmontosaurus individuals enclosed by an ultra-thin clay layer that retained external anatomy. The clay adhered to decaying skin and biofilm, producing a high-fidelity external mold that preserved minute features such as scale patterning and skin folds.
The specimens were imaged using a suite of modern modalities—high-resolution CT, X-ray radiography and photogrammetry—enabling the team to build three-dimensional soft-tissue models and digitally drape them over the skeletons. That workflow permitted measurements of scale diameters (most 1–4 mm) and mapping of dorsal structures from skull to tail, revealing a crest that becomes a series of spike-like projections aligned with vertebrae.
Perhaps the most unexpected result was the foot anatomy. Forelimbs show a single central, laterally enveloping hoof with a ventral triangular frog structure, while hind feet present three wedge-shaped hooves with a fleshy posterior heel. The researchers interpret these as functional adaptations: forelimb hooves for weight transfer or substrate interaction and tridactyl hind hooves supporting locomotion and weight-bearing.
Beyond Edmontosaurus, fieldwork recovered a T. rex preserved in a life-like pose and a Triceratops mummy with much larger scales and thicker, unwrinkled skin. Preliminary taphonomic differences—Edmontosaurus showing a death pose consistent with days-to-week delay before burial, versus a possibly live burial for the T. rex—suggest variable processes even within the same depositional pocket.
Analysis & Implications
The discovery of hoof-like integumentary structures in Edmontosaurus challenges assumptions about the uniqueness of mammalian hooves and highlights convergent solutions to similar biomechanical problems. If the morphology near the toe and the presence of a frog-like pad are confirmed across multiple specimens, it implies that ungulate-style weight distribution evolved at least twice in large terrestrial vertebrates. That would revise discussions about locomotor evolution in archosaurs and the functional anatomy of hadrosaur forelimbs and hind limbs.
Fine-scale skin preserved at sub-millimeter resolution alters how paleontologists reconstruct dinosaur physiology and thermoregulation. Scales just millimeters across and an extremely thin dermis indicate different heat-exchange properties than thick, keratinized hides; combined with body size and possible vascularization, these data feed models of heat balance, water loss and ecological niche partitioning between contemporaneous herbivores, such as Triceratops and Edmontosaurus.
Taphonomically, clay templating as a mechanism for exceptional preservation in fluvial settings expands the range of depositional scenarios that can produce soft-tissue fossils. The local sedimentation spike in the Lance Formation demonstrates that rapid, repeated flooding can bury and mask carcasses in a way that preserves external anatomy at near-microscopic fidelity. This insight will guide targeted field surveys in other fluvial or deltaic strata of similar age.
Practically, the combination of modern imaging and digital restoration sets a new bar for paleo-reconstruction. Three-dimensional, data-driven skins reduce reliance on speculative artistic inference and allow testable hypotheses about integument, posture, and musculature to be built and compared to biomechanical models.
Comparison & Data
| Feature | Edmontosaurus (this study) | Triceratops (prelim.) |
|---|---|---|
| Typical scale diameter | 1–4 mm (up to ~10 mm on lower tail) | ~10× larger than Edmontosaurus scales (prelim.) |
| Skin thickness / texture | Thin, wrinkled | Thicker, no wrinkles (prelim.) |
| Hoof/foot morphology | Fore: single central hoof with frog; Hind: three wedge-hooves + fleshy heel | Data pending detailed study |
| Taphonomic pose | Death pose; likely died up to a week before burial | T. rex: life-like pose (possible live burial); Triceratops: under study |
The table summarizes measured scale sizes and preliminary observations. Scale and skin contrasts between Edmontosaurus and Triceratops—two large herbivores coexisting in the same locality—raise questions about niche differentiation, defensive strategies, or distinct thermoregulatory adaptations despite similar body mass and environment.
Reactions & Quotes
Sereno framed the finds as a correction and refinement of a century of images:
“We finally nailed down the way it truly looked,”
Paul C. Sereno, University of Chicago (lead author)
Context: Sereno emphasized that combining archival detective work with modern imaging allowed the team to reconcile earlier, conflicting reconstructions and demonstrate concrete anatomical features rather than conjecture.
An external paleontologist reflected on the evolutionary implications:
“The presence of hoof-like structures suggests unexpected convergences in large terrestrial vertebrates,”
Independent paleobiologist (comment)
Context: This comment stresses that similar functional demands (weight support, substrate interaction) can drive repeated emergence of hoof-like anatomy, prompting reevaluation of locomotor evolution among archosaurs.
Unconfirmed
- The hypothesis that the T. rex was buried alive is preliminary and requires additional taphonomic and histological evidence before confirmation.
- Whether hoof-like structures occurred broadly across hadrosaurids or represent a local adaptation in these individuals is unresolved pending broader sampling.
- The precise cause of the unusually high sedimentation rate in the mummy zone is inferred (frequent flooding) but not yet demonstrated by independent sedimentological proxies.
Bottom Line
The Wyoming Edmontosaurus mummies provide an unprecedented, data-rich view of external anatomy in a large Cretaceous herbivore, updating century-old restorations with measurable details: millimeter-scale scales, a crest-to-spike dorsal transition, and distinct hoof-like feet. These anatomical revisions have immediate consequences for functional reconstructions, prompting new hypotheses about locomotion, behavior and ecological partitioning among Late Cretaceous herbivores.
Methodologically, the study highlights how archival field work, targeted prospecting and modern imaging combine to unlock soft-tissue data previously thought unobtainable in fluvial settings. As the team prepares reports on the T. rex and Triceratops mummies, paleontology may enter a phase in which high-fidelity soft-tissue evidence routinely reshapes long-standing anatomical and evolutionary interpretations.