Two "mummies" of the late Cretaceous dinosaur Edmontosaurus annectens preserve a fleshy ridge on the neck and trunk, a series of interlocking spines on the flanks and tail, and hooves on the toes of the hind feet.[1][2] These skin, spine, and hoof structures are preserved as a thin (<1 mm) clay template that formed on the surface of the buried carcass during decomposition before the loss of soft tissues and organic compounds.[1][2][6] In contrast to permineralized bones, the skin is preserved as an outer clay mask, a process previously documented only in anoxic marine environments.The study revealed a continuous midline beginning with a fleshy ridge on the neck and trunk, transitioning into a series of spines on the tail, where each spine lies over a single vertebra.2][3][4][5] The hind feet have three toes ending in wedge-shaped, flat-bottomed hooves similar to those of a horse; the fore feet touch the ground only with the hooves, while the hind feet have a fleshy heel pad.[3][4][5] One mummy is a late juvenile, the first subadult dinosauria mummy with a complete body outline, the other an adult with a complete row of spines on the tail and the earliest known hooves in a tetrapod.[2][3] The skin on the lower body and tail has larger polygonal scales the size of small pebbles,[4] and wrinkles on the ribs suggest thin skin.[4] These findings make E. annectens the first confirmed hoofed reptile and the earliest terrestrial vertebrate with hooves.