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More than a century after their discovery in eastern Wyoming, duck-billed Edmontosaurus annectens skeletons have yielded a surprise: paleontologists at the University of Chicago found mummified outlines beneath a clay “mask,” not fossilized soft tissue, according to a study in Science. Microbe-built clay molds preserved skin, spikes, hooves and a crest, with uniform layers bound by sandstone—unlike typical soft-tissue fossils from oxygen-poor settings. Newly examined specimens include the first subadult dinosaur mummy with a fully preserved outline and an adult that retains a complete tail spike row and the earliest known tetrapod hooves, revealing a more complex hide.

Prepared by Olivia Bennett and reviewed by editorial team.