New Paleontological Study Sheds Light on the True Nature of Wyoming’s “Dinosaur Mummies”
In a groundbreaking reevaluation of some of the most iconic fossil discoveries, recent paleontological research has unveiled new insights into the preservation process behind the so-called “dinosaur mummies” found in Wyoming. These specimens—remarkably detailed duck-billed dinosaurs, Edmontosaurus annectens—show skin, spikes, and hooves that initially seemed to be fossilized soft tissue. However, advanced analyses have revealed that this astonishing preservation is not due to traditional fossilized flesh, but rather the result of a delicate clay templating process created by microbial activity during decay.
Soft-tissue fossilization is typically associated with fine-grained, low-oxygen environments such as marine or lagoon sediments, where the limited oxygen inhibits decomposition and allows delicate structures like feathers or skin to mineralize. The Edmontosaurus “mummies” defied these expectations, having been unearthed in coarse, oxygenated fluvial deposits—river sediments—posing a persistent riddle regarding how their soft integumental features survived.
Researchers, including Paul Sereno and collaborators, turned to thorough historical investigations to approximate the original excavation sites of these remarkable specimens, first uncovered over a century ago in eastern Wyoming. The new fieldwork at the rediscovered site yielded exciting additional material, including both juvenile and adult Edmontosaurus specimens with preserved external outlines. Notably, the discovery of a late juvenile represents the first confirmed subadult dinosaur mummy and reveals a complete fleshy silhouette, including a midline neck and trunk crest previously unknown in hadrosaurids.
The adult Edmontosaurus specimen carries equally significant revelations. It is the first hadrosaurid found with a complete row of tail spikes intact and exhibits the earliest known occurrence of hooves within any tetrapod lineage—marking this dinosaur as the earliest reptile to have hooved feet. These features collectively indicate a far more complex epidermal morphology than traditional restorations depicted, challenging long-standing assumptions about dinosaur integuments’ structure and function.
Comparative anatomy with extant reptiles, particularly modern squamates (lizards and snakes), suggests that the midline crests and tail spikes likely had functional roles and morphological parallels within these living groups. This comparative framework provides a context for hypothesizing about the behavioral or ecological functions of these epidermal structures in Edmontosaurus, hinting at display, thermoregulation, or defense mechanisms.
At the core of the study lies the revelation that the preservation of these anatomical features is not a matter of true organic tissue fossilization. Using an array of cutting-edge analytical techniques—including optical microscopy, computed tomography (CT), electron microscopy, and X-ray spectroscopy—the team meticulously examined the specimens’ integument and surrounding sediment. Their results showed no detectable remnants of original organic compounds within the clay or sandstone matrix.
Instead, the soft-tissue impressions exist as ultra-thin clay films, generally less than one millimeter thick, that have faithfully reproduced the external surfaces of the decaying carcasses. This clay layer forms a precise negative mold, preserving the three-dimensional integumentary details. The evidence strongly suggests that a bacterial biofilm mediated this templating process: as the dinosaur carcasses decayed, biofilms fostered the deposition of fine clay minerals directly adjacent to the soft tissues, capturing intricate external morphologies even within a highly oxygenated, fast-moving river environment.
This mode of preservation drastically expands the recognized range of environments conducive to exceptional soft-tissue fossilization. Clay templating allows for exquisite external detail retention in contexts previously considered inhospitable to soft tissue preservation, such as coarse-grained fluvial deposits dominated by high oxygen exposure and active decay. Consequently, the study challenges and broadens traditional paradigms within taphonomy—the study of fossilization processes—and invites a reevaluation of other fossil specimens preserved in similar depositional settings.
This discovery holds profound implications not only for understanding Edmontosaurus anatomy and paleobiology but also for refining the mechanisms underlying fossil preservation. The realization that microbes can actively participate in shaping the fossil record by mediating mineral deposition alters the interpretation of soft-tissue fossilization and may prompt reexamination of other “soft-tissue” fossils worldwide.
Moreover, the presence of hooves on a dinosaur represents an evolutionary novelty, suggesting convergent or unique morphological adaptations within dinosaurian locomotion and weight distribution. Such functional anatomical insights pave the way for further biomechanical studies assessing how these specialized structures influenced Edmontosaurus’ terrestrial capabilities and ecological interactions.
The detailed midline crest and tail spikes also encourage fresh perspectives on dinosaur integument diversity and complexity. Where earlier reconstructions portrayed hadrosaurids with relatively simple skin covers, these preserved specimens unveil a mosaic of specialized epidermal features analogous in some respects to reptiles alive today, reinforcing ideas about the dynamic evolutionary history of dinosaur skin and appendages.
Beyond its paleobiological significance, this research exemplifies the importance of integrating multidisciplinary approaches—combining historic archival work, field paleontology, and state-of-the-art laboratory analytics—to resolve longstanding paleontological enigmas. The study’s success in pinpointing original fossil sites after more than one hundred years and uncovering new material underscores the enduring value of historical records in scientific discovery.
As researchers continue to investigate these clay-templated mummies, they may uncover additional nuances regarding microbial roles in fossilization, the chemical pathways involved in mineral deposition, and the preservation potential of other extinct taxa. This expanding knowledge promises to refine our understanding of the fossil record’s fidelity and the intricate interplay between biology, chemistry, and sedimentology in deep time.
In summary, the latest findings illuminate a novel preservation mechanism whereby delicate clay layers deposited by biofilms encapsulate the external forms of dinosaur carcasses during decay, rather than preserving original soft tissues. This mechanism accounts for the exceptional three-dimensional soft-tissue detail of Edmontosaurus “mummies” recovered from oxygen-rich river deposits, overturning prior assumptions about their fossilization and revealing unexpected anatomical complexity in this iconic duck-billed dinosaur.
The insights gained from this work not only enrich knowledge of hadrosaurid biology and taphonomy but also expand the horizons of fossil preservation science, encouraging renewed scrutiny of other fossil specimens and fostering broader appreciation of the microbial contribution to the fossil record.
Subject of Research: Paleontological study of duck-billed dinosaur Edmontosaurus annectens soft tissue preservation and fossilization mechanisms
Article Title: Duck-billed dinosaur fleshy midline and hooves reveal terrestrial clay-template “mummification”
News Publication Date: 23-Oct-2025
Web References: DOI: 10.1126/science.adw3536
Keywords: Edmontosaurus annectens, dinosaur mummies, soft tissue fossilization, clay templating, biofilms, hadrosaurid anatomy, taphonomy, hooved reptile, midline crest, tail spikes, fluvial deposits, microbial fossils
Tags: advanced paleontological analysis techniquesclay templating in fossilsdinosaur mummies paleontologyduck-billed dinosaur discoveriesEdmontosaurus annectens fossilsfluvial sediment fossil findingsiconic fossil discoveries re-evaluatedjuvenile and adult dinosaur specimensmicrobial activity in decaypreserved dinosaur skin and hoovessoft-tissue fossilization processesWyoming dinosaur excavation history
