Paleontologists have made a significant discovery regarding duck-billed dinosaurs, specifically Edmontosaurus annectens, which were unearthed in eastern Wyoming over a century ago. Recent research indicates that these fossils are exceptionally well-preserved, containing fleshy body parts embedded in thin layers of clay. This finding was detailed in a paper published last week in the journal Science.

The Edmontosaurus, known for its long skull resembling a duck's bill, was first discovered in the early 1900s. A team from the University of Chicago reexamined these fossils and found that they include not only bones but also mummified body parts protected by a clay mask. The researchers described the preserved pieces as “stunningly preserved” and noted the presence of skin, spikes, and hooves among the bones.

Importantly, the fleshy parts are not fossilized flesh. Instead, they are delicate clay molds formed by microbial activity as the animals decayed. The clay layers are bound by sandstone, which differs from typical soft tissue preservation that occurs in fine-grained, oxygen-poor environments like lagoons or seabeds. In those conditions, delicate features such as feathers and skin can become fossilized.

Initially, scientists believed the specimens were fossilized skin and body parts due to their discovery in coarse, oxygenated river deposits. However, further examination of the original skeletons, along with the findings of two additional mummified E. annectens—one juvenile and one adult—revealed a different story.

The juvenile specimen is notable for being the first subadult dinosaur mummy discovered, showcasing a fully preserved fleshy outline, including a neck and trunk crest. The adult specimen is the first hadrosaurid to retain its complete tail spike row. Additionally, it is recognized as the earliest known tetrapod with hooves, marking a significant point in the evolutionary history of reptiles.

The midline crest and tail spikes of E. annectens suggest a more complex hide than previously thought, according to the researchers. They also noted that this species shares functional and morphological similarities with some modern squamates, which include lizards and snakes. This research sheds new light on the anatomy and preservation of these ancient creatures, enhancing our understanding of their biology and evolution.