Paleontologists at the University of Chicago have uncovered two exceptionally well-preserved fossils of the duck-billed dinosaur Edmontosaurus annectens in eastern Wyoming. They say the two duck-billed dinosaur are so well-preserved that parts of their skin and soft tissue remain encased in thin layers of clay.
The remarkable condition of these 66-million-year-old fossils offers rare insight into the dinosaurs’ appearance, including details like scales, spikes, and hoof-like toes. Researchers say the clay coating and microbial activity helped protect the animals’ bodies after death, preserving features almost never seen in fossils.
These specimens include not just bones but detailed external features—what some call “dinosaur mummies”—because their skin, spikes and even hoof-like toes were preserved under a thin sheet of clay. The animals’ external surfaces weren’t preserved as typical hardened tissues.
Instead, a clay layer barely one-hundredth of an inch thick formed over their decaying carcasses, aided by microbial biofilms, capturing their skin and bodily contours. This process is indeed contrary to the traditional way fossils usually form. The adult dinosaur had hoof-like coverings on its hind toes — a structure previously unknown in any reptile or dinosaur.
It also appears to have had a fleshy crest along its neck and back, and a row of spikes down the tail. Specimens of Edmontosaurus annectens are known for their long skull that resembles a duck's bill, were found in eastern Wyoming in the early 1900s.
These findings change how scientists reconstruct dinosaurs like Edmontosaurus. Instead of just relying on bones, they now have actual contours of soft tissue and skin patterns. These actually help paint a richer and more accurate picture of how the animal looked, moved, and lived.
The discovery also expands our understanding of where and how such preservation can occur. Usually, soft-tissue preservation happens in low-oxygen, fine-grain sediment environments. But these “mummies” were found in coarse river deposits, showing that exceptional preservation can happen in more varied conditions than previously thought.
