Exceptionally Preserved Dinosaur “Mummies” in Wyoming Reveal Skin, Hooves and Tail Spikes

Researchers have identified remarkably intact remains of Edmontosaurus annectens discovered in eastern Wyoming, exposing details of skin texture, tail spikes and even hooves that were hidden for more than a century. The team from the University of Chicago reexamined skeletons unearthed in the early 1900s and, in a study published last week in the journal Science, described how thin clay coatings formed by microbial activity preserved the animals’ external anatomy in striking detail.

The hadrosaur fossils, originally recovered from coarse, oxygen-rich river sediments, were long thought to contain only bones. Fresh analysis, however, showed that a uniform layer of fine clay surrounds several specimens, effectively creating natural body casts. The clay was produced as microbes consumed decaying soft tissue, leaving behind a delicate mold bound by sandstone. This preservation route differs from the more familiar pathway in which soft parts fossilize in oxygen-poor, fine-grained settings such as lagoons or seabeds.

Among the newly documented features are well-defined scales, raised midline crests, a complete row of tail spikes and, for the first time in any reptile, fully formed hooves. The adult individual retains its entire spike series along the tail, making it the first hadrosaurid with that attribute intact. The same specimen also represents the earliest known tetrapod with hooved feet, expanding the understanding of locomotion strategies among late Cretaceous dinosaurs.

A separate juvenile skeleton offers another first: it is the only subadult dinosaur mummy with a fully preserved fleshy outline, including a neck and trunk crest. The researchers note that the crest and tail spikes indicate a far more complex hide pattern than earlier reconstructions suggested, implying that visual display or thermoregulation might have played a larger role in the species’ biology than previously assumed.

Study co-author Tyler Keillor prepared high-resolution digital models that reconstruct the animals’ original form. These models confirm that the “fleshy” material is not fossilized tissue but ultra-thin clay, sometimes no thicker than a sheet of paper, that perfectly follows the contours of the vanished skin. In several limb segments, the clay caps the terminal toe bones, outlining distinct hoof structures at the foot tips.

The team also evaluated two mummified E. annectens specimens recovered in recent decades—a juvenile and an adult—that display the same preservation style. Comparison with the historic finds suggests that clay coating may be more common in river-deposited dinosaur remains than previously recognized. Because the process depends on microbial biofilms forming early template layers, carcasses must have been quickly buried yet still exposed to enough oxygen to sustain microbial colonies, a combination once thought unfavorable for soft-part conservation.

Imagem: Internet

Functional parallels between the hadrosaur hide and certain living squamates support the view that convergent evolution produced similar skin adaptations in unrelated reptile groups. Further research will test whether other hadrosaurids or contemporaneous species experienced comparable preservation, potentially revising interpretations of late Cretaceous ecosystems.

The discovery underscores the importance of reexamining legacy collections with modern techniques. Advanced imaging and geochemical analyses can uncover information missed by earlier generations of field workers, who often focused exclusively on skeletal material. As paleontologists refine methods for detecting soft-tissue proxies, the number of species known from “mummified” remains could rise substantially.

Additional background on hadrosaur anatomy and preservation methods is available from the Smithsonian Institution’s National Museum of Natural History, which hosts extensive dinosaur research resources.

Crédito da imagem: Tyler Keillor/Fossil Lab