Two new specimens of Edmontosaurus annectens preserve fine details of scales and hooves

Paleontologists examined two exceptional specimens of the duck-billed dinosaur from the late Cretaceous Edmontosaurus appendix. Using a range of imaging techniques, they reconstructed the fleshy appearance of the species in its living state, from a tall crest on the neck and trunk to a row of spikes on its tail and hooves sheathing its toes; combined with fossilized footprints, the appearance of Edmontosaurus appendix is now at your fingertips.

“This is the first time we have had a complete, detailed view of a large dinosaur that we can really have confidence in,” said Professor Paul Sereno of the University of Chicago, lead author of the study.

“The Wyoming badlands, where the discoveries were made, are a unique ‘mummy zone’ that holds more surprises thanks to the fossils collected over years of visits by teams of university students.”

Using historical photos and field research, Professor Sereno and his colleagues relocated the sites in east-central Wyoming where several famous dinosaur “mummies” were discovered in the early 20th century, mapping a compact “mummy zone.”

In these piled river sands, they excavated two new “mummies” of Edmontosaurus appendix — one juvenile and one adult — with large, continuous areas of preserved external skin surface.

By working with these specimens, they pieced together a complete, fleshy profile of the species.

“The two specimens complement each other wonderfully,” said Professor Sereno.

“For the first time, we were able to see the entire profile rather than scattered areas.”

Paleontologists identified a continuous midline that began as a fleshy ridge along the neck and trunk and transitioned above the hips into a single row of spikes running down the tail – each spike positioned on a single vertebra and fitted to each other.

The lower body and tail had the largest polygonal scales, although most were tiny pebble-like scales measuring only 1–4 mm in diameter, surprisingly small for a dinosaur measuring over 12 m (40 ft) in length.

The wrinkles preserved on the ribcage suggest that the skin of this duckbill was thin.

The hind legs of the largest “mummy” contained the biggest surprise: hooves.

The tip of each of the three hind toes was enclosed in a wedge-shaped hoof with a flat bottom like that of a horse.

The researchers used CT scans of the specimen’s feet and 3D images of the best-preserved duckbill print from the same period, adapting the former to the latter.

Using information from both sources, they accurately reconstructed the appearance of the hind leg.

Unlike the forefoot which only touches the ground with its hooves, the hind legs have a fleshy heel behind the hooves.

“There are so many amazing ‘firsts’ preserved in these duck-billed ‘mummies’ – the first documented hooves in a land vertebrate, the first confirmed hoofed reptile, and the first four-legged animal with different forelimb and hindlimb postures,” Professor Sereno said.

The team’s paper was published today in the journal Science.

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Paul C. Sereno and others. 2025. The duck-billed dinosaur’s fleshy midline and hooves reveal clay-like terrestrial “mummification.” Sciencepublished online October 23, 2025; doi: 10.1126/science.adw3536