Natural Mummification (Dinosaur Mummy)

The concept of natural mummification in paleontology traces back to the early twentieth century. In 1908, fossil collector Charles Hazelius Sternberg and his three sons discovered an exceptionally preserved specimen of Edmontosaurus annectens (then classified as Trachodon) near Lusk, Wyoming, in the Lance Formation. The specimen, cataloged as AMNH 5060, was acquired by the American Museum of Natural History, where Henry Fairfield Osborn described it in 1911 and coined the term 'dinosaur mummy' to highlight its remarkable preservation of skin impressions tightly adhering to the skeleton. Osborn noted hundreds of polygonal tubercle impressions across the body. The specimen remains on display at the AMNH and represents one of the most complete dinosaur fossils ever recovered, with approximately two-thirds of the body surface covered in skin traces.

Shortly afterward, in 1910, the Sternberg family discovered a second Edmontosaurus mummy from the same region, which was sold to the Senckenberg Naturmuseum in Frankfurt, Germany (cataloged as SMF R 4036). This specimen, often called the 'Senckenberg mummy,' also preserves extensive skin impressions and has been on continuous display for over a century.

Research over the past century has revealed that dinosaur mummies do not arise from a single preservational pathway. At least three distinct mechanisms have been identified, each associated with different environmental conditions and resulting in different modes of soft-tissue representation.

1. Desiccation and Deflation

This pathway, elucidated in detail by Drumheller et al. (2022) through study of the Edmontosaurus mummy NDGS 2000 (nicknamed 'Dakota'), involves extended subaerial exposure of a carcass for weeks to months. During this interval, predators, scavengers, and decomposers breach the body wall, creating openings that allow gases, fluids, and microbial byproducts to escape. The internal soft tissues (muscles, organs, viscera) are consumed or decompose, leaving behind more durable dermal tissues draped directly over the skeleton. CT imaging of NDGS 2000 confirmed that the skin is deflated—not compressed by sediment weight—with bones undistorted in three dimensions and no internal soft tissues present. Crucially, this specimen preserves the first documented evidence of carnivore bite marks on dinosaurian soft tissue, including crocodyliform-diagnostic bisected tooth marks on the humerus. The desiccation-and-deflation pathway does not require rapid burial or exceptional environmental conditions, which explains why dinosaurian skin, while uncommon, is not exceptionally rare in the fossil record.

2. Rapid Burial

Rapid burial in the perimortem to early postmortem interval removes remains from surface taphonomic processes and limits oxygen access, slowing microbial decomposition. Mummies preserved via this pathway are proposed to retain three-dimensional body form and potentially internal organs. The Brachylophosaurus canadensis mummy 'Leonardo' (MOR 7020), discovered in 2000 near Malta, Montana, in the Judith River Formation, has been cited as a possible example, with approximately 90% of its body covered by soft-tissue traces including possible gut contents and parasites. However, analyses have shown complications: no obvious internal organs were observed, clay content within the body cavity exceeded that in surrounding sediment, and the body wall appeared to have been breached before final burial, suggesting the preservational history may be more complex than simple rapid entombment.

3. Aqueous Anoxia

Remains deposited in anoxic (oxygen-free) to hypoxic (low-oxygen) water experience minimal scavenging and depressed microbial activity. This can occur in both shallow stagnant water bodies and in deeper settings with density stratification. The iconic Borealopelta markmitchelli (TMP 2011.033.0001), a nodosaurid ankylosaur discovered in 2011 during oil sands mining near Fort McMurray, Alberta, exemplifies this pathway. Dating to approximately 110 million years ago (Early Cretaceous), the specimen preserves three-dimensional armor, skin with original melanin-based pigmentation (countershading pattern), and even stomach contents showing a last meal dominated by ferns. The carcass is believed to have been transported to a marine setting where it sank to the anoxic seafloor, inhibiting decomposition and allowing rapid mineralization.

A landmark study published in Science by Sereno et al. (2025) introduced 'clay templating' as a previously unrecognized preservation mechanism for dinosaur mummies. Working with two newly excavated Edmontosaurus annectens specimens from a 'mummy zone' in east-central Wyoming—the same region where Sternberg made his discoveries over a century earlier—the team demonstrated that the 'skin' on many dinosaur mummies is not fossilized tissue at all. Instead, it is a sub-millimeter-thick external clay film that formed on the carcass surface shortly after burial. The process involves a biofilm on the decaying carcass surface electrostatically attracting clay minerals from surrounding wet sediment, creating a faithful three-dimensional mold of the animal's exterior. Once the organic material decays, the clay template remains as a precise record of scales, wrinkles, and fleshy structures.

This discovery has profound implications. The two new specimens revealed previously unknown anatomical features of Edmontosaurus annectens: a continuous fleshy midline crest over the neck and trunk that transitions into a row of discrete spikes along the tail, wedge-shaped hooves on the hind feet (the first confirmed hooves in any reptile and the earliest documented hooves in a terrestrial vertebrate), and very small pebble-like scales (1–4 mm) over most of the body despite the animal's potential adult length exceeding 12 meters. CT scans, thin sections, X-ray spectroscopy, and clay mineral analyses all supported the clay-templating model.

A striking pattern in the paleontological record is the disproportionate abundance of hadrosaur mummies relative to other dinosaur groups. Several factors contribute to this bias. Hadrosaurs were among the most abundant large herbivores in Late Cretaceous ecosystems of North America, increasing the baseline probability of exceptional preservation. Their skin appears to have been particularly durable and resistant to early decay, possibly owing to its composition of densely packed, keratinized polygonal tubercles. Additionally, the desiccation-and-deflation pathway described by Drumheller et al. (2022) relies on commonplace biostratinomic processes rather than extraordinary events, suggesting that dermal preservation in hadrosaurs may have been a relatively routine taphonomic outcome. The comparative rarity of facial skin preservation in these mummies is consistent with this model, as predators and decomposers preferentially target natural body openings (mouth, eyes, nasal passages) to access internal tissues.

Beyond Edmontosaurus and Borealopelta, several other dinosaur mummy specimens have contributed significantly to paleontological knowledge. 'Leonardo' (Brachylophosaurus canadensis, MOR 7020) from Montana preserves extensive skin and possible gut contents. 'Dakota' (Edmontosaurus sp., NDGS 2000) from North Dakota provided the first evidence of carnivore interactions with soft dinosaurian tissue. The Sereno et al. (2025) specimens from Wyoming revealed hooves and crest structures. A Thescelosaurus neglectus specimen nicknamed 'Wilo' from South Dakota preserves what was initially interpreted as a fossilized heart, although this interpretation has been debated. More recently, additional mummified hadrosaur specimens continue to be discovered, underscoring that natural mummification was not as rare an event as once assumed.

Natural mummification provides paleontologists with direct evidence of soft-tissue anatomy that cannot be inferred from bones alone. Skin texture, scale morphology, body contour, integumentary structures such as crests and spikes, and even coloration patterns can be documented from mummified specimens. The preservation of biomolecules—degraded proteins, possible melanin, and other organic compounds—in some mummies (particularly NDGS 2000 and Borealopelta) opens avenues for molecular paleontology and paleobiochemistry. Furthermore, the recognition that multiple taphonomic pathways can produce mummies has broadened the search image for soft-tissue preservation, encouraging researchers to look for such evidence in settings previously considered unfavorable.

Dinosaur mummies have consistently captured public imagination. The 1908 discovery of AMNH 5060 was a media sensation in its day. The 2007 announcement of 'Dakota' and the 2017 unveiling of Borealopelta at the Royal Tyrrell Museum each generated worldwide media coverage. The 2025 Science publication by Sereno et al., with its revelation of hooves and clay-template preservation, attracted extensive public attention and was timed to coincide with the Halloween season, emphasizing the 'mummy' connection. These specimens serve as powerful tools for science communication, making the abstract deep-time record tangible and relatable to general audiences.