New ‘mummified’ dinosaur specimens found in eastern Wyoming

Scientists working in Wyoming found two new “mummified” dinosaur fossils that show skin and the oldest confirmed hooves in reptiles.

The original set of “mummified” dinosaurs, specimens of the duck-billed herbivore Edmontosaurus annectens, were found in 1908 and 1910 in eastern Wyoming.

New excavations in the area turned up two other fossils of the same species that show more skin as well as hooves, according to a study published last week on the site of the journal Science.

One of the specimens is the first juvenile “dinosaur mummy” on record and the first to have the visage of its “fleshy midline over the trunk” preserved, while the other, an adult, is the first to show a “spike row” of bones from the hips to the tip of its tail, the authors said.

The adult specimen also stands out for its hooves, a body part not found in any fossilized species older than Edmontosaurus annectens.

“There are so many amazing ’firsts’ preserved in these duck-billed mummies — the earliest hooves documented in a land vertebrate, the first confirmed hooved reptile, and the first hooved four-legged animal with different forelimb and hindlimb posture,” said senior author Paul Sereno, a University of Chicago professor of organismal biology and anatomy, in a release from the school.

While the journal refers to the fossils as mummies, they do not contain actual tissue like a mummified human from Ancient Egypt or elsewhere would. Rather, the animal’s skin and body parts were rendered into an image on a layer of clay while the dinosaur’s flesh was still decomposing.

“This is a mask, a template, a clay layer so thin you could blow it away. It was attracted to the outside of the carcass in a fluke event of preservation,” Mr. Sereno said.

The clay template, the authors said in the study, came about via a process that has only ever been seen in marine fossilization environments, which lack oxygen.

Mr. Sereno hypothesized to Scientific American that the two duck-billed dinosaurs first died and then were dried out in a drought before a flood engulfed them in new sediment.

Bacteria then latched onto their corpses and created a biofilm which in turn created the clay layer; the carcasses then decayed and were washed away, leaving only the clay layer to ultimately become the fossil found by the scientists.