New Wyoming “Dinosaur Mummies” Reveal Unexpected Skin, Hooves and Preservation Pathway
Two unusually well-preserved duck-billed dinosaur specimens recovered in eastern Wyoming provide a new look at hadrosaur anatomy and clarify how large terrestrial animals can leave detailed soft-tissue impressions. The finds, led by researchers from the University of Chicago, include a late juvenile and an adult Edmontosaurus annectens recovered from a zone the team calls the “mummy zone.”
Recovering a lost site
The site’s significance traces to early 20th-century collector C. H. Sternberg, who documented exceptionally preserved hadrosaur remains in 1908. Over subsequent decades the exact location of those quarries was lost because photographic materials were misfiled in archival publications. The research team reexamined historical photos, correspondence and local memories to narrow the site to a roughly 10-kilometer area and relocate the fossil-bearing exposures.
What the specimens show
The newly recovered specimens preserve clear clay-cast outlines of skin and other soft tissues rather than original organic tissues. They display a complex midline crest and a fully preserved row of tail spikes, features that differ from many prior reconstructions of duck-billed dinosaurs. The adult also preserves a thin clay layer forming a hoof-like cap over the toe bones, representing the earliest known reptilian hoof morphology in the fossil record.
How the impressions formed
Detailed analyses using optical imaging, CT, electron microscopy and X-ray spectroscopy indicate the preserved outlines are thin clay layers trapped between sandstone. The team proposes a rapid burial scenario in which seasonal river dynamics and microbial biofilms produced clay templates that recorded the animals’ external surfaces during early decay. No organic tissues were detected within the clay layers; preservation is interpreted as a mineralized clay impression rather than true soft-tissue fossilization.
This mechanism expands the range of environments where paleontologists might expect to find soft-tissue outlines: instead of requiring long-term anoxic lagoonal conditions, clay-template preservation can occur quickly in river sediments under the right conditions.
Additional discoveries and implications
Alongside the hadrosaurs, excavations in the same area produced a Triceratops skeleton with flesh imprints and a fully articulated Tyrannosaurus rex. The co-occurrence illustrates the diversity of integument types—scales, smooth skin and feathers—within the same late Cretaceous environment.
The team plans further papers that will detail the broader taphonomic context and the anatomical implications for all three species. The lead researcher emphasized that the finds highlight both the value of reexamining historical records and the continued potential for significant discoveries in well-studied regions.
