In a groundbreaking study, paleontologists have revealed that what were once believed to be 66 million-year-old dinosaur mummies in Wyoming are actually the result of an extraordinary clay masking process. The research focuses on the Lance Formation, a site known for its rich deposits of prehistoric fossils, where two remarkably preserved specimens of the duck-billed dinosaur Edmontosaurus annectens were unearthed in 2000 and 2001.
Dr. Paul Sereno, a paleontologist at the University of Chicago and lead author of the study, described the region as “the mummy zone.” This area, spanning less than 10 kilometers (6 miles), has yielded at least six well-preserved dinosaur specimens, showcasing intricate details of skin, hooves, and spikes. The findings challenge previous assumptions about the nature of these fossils and clarify the preservation process.
In the early 1900s, fossil hunter Charles Sternberg discovered two specimens of Edmontosaurus in the same formation. The skeletons were so well preserved that Sternberg and paleontologist H.F. Osborn could identify large areas of skin with visible scales. Despite their impressive condition, Osborn noted in 1912 that the remains were not actual dehydrated skin like that of Egyptian mummies. The question remained: how had these features been preserved?
Decades later, Sereno and his team employed advanced techniques including CT scanning, 3D imaging, and electron microscopy to investigate the specimens. They discovered that instead of remnants of soft tissue, the fossils were covered by a thin layer of clay, less than one-hundredth of an inch thick. “It’s so real-looking, it’s unbelievable,” Sereno remarked about the clay’s appearance.
The study proposes a new terminology, suggesting that the term “rendering” is more accurate than “impression” to describe the detailed clay coating. The researchers outlined the conditions necessary for such preservation, noting that during the Late Cretaceous Period, the climate oscillated between drought and heavy rains. The initial cause of death for these dinosaurs was likely dehydration from drought, followed by burial in sediment during a flash flood.
Following their deaths, the carcasses would have been covered by a film of bacteria that attracted clay particles from the surrounding soil. This interaction led to the formation of a clay mask that preserved detailed features, including the dinosaur’s scales and skin textures. Dr. Anthony Martin, from Emory University, highlighted the significance of clay minerals in creating accurate replicas of biological surfaces.
Experts in the field, such as Dr. Stephanie Drumheller-Horton from the University of Tennessee, emphasized the importance of understanding the fossilization process. “Dinosaur mummies have been known for over one hundred years,” she noted, “but understanding how they fossilized is crucial for future discoveries.”
The examination of the two recently discovered mummies allowed Sereno and his team to provide a detailed reconstruction of the Edmontosaurus. Their analyses revealed that the dinosaur, which could grow over 12 meters (40 feet) in length, had a fleshy crest along its neck and back, along with spikes running down its tail. The clay mask also indicated that this dinosaur possessed hooves, marking it as the oldest known land animal with this feature and the first hooved reptile.
“Sorry, mammals, you didn’t invent it,” Sereno joked, referencing the significance of this discovery. The research, published in the journal Science on March 15, 2024, marks an important advancement in paleontology, shedding light on the appearance of these ancient creatures and their preservation process.
As scientists continue to explore fossil sites like the Lance Formation, the insights gained from this study will enhance the understanding of dinosaur morphology and the environmental conditions that facilitated their preservation.
