In a groundbreaking development, scientists have revealed that the so-called dinosaur “mummies” discovered in the Lance Formation of eastern Wyoming are not preserved skin but rather intricate clay casts. This finding sheds light on the preservation processes that occurred during the Late Cretaceous Period, approximately 66 million years ago, and enhances understanding of dinosaur morphology.
The Lance Formation, a rich fossil site, has long intrigued paleontologists. In a study led by Dr. Paul Sereno, a professor of organismal biology and anatomy at the University of Chicago, the team investigated two specimens of the duck-billed dinosaur Edmontosaurus annectens, unearthed in 2000 and 2001. These specimens, referred to as “mummies,” had previously shown remarkable preservation, including visible scales and features that typically degrade over millions of years.
Historically, paleontologists have been captivated by the quality of preservation in this area. The initial discoveries were made by fossil hunter Charles Sternberg, who, in the early 1900s, found well-preserved skeletons that displayed what appeared to be skin and a fleshy crest along the neck. In a statement, Sereno described the original find as “the greatest dinosaur mummy — until maybe the juvenile that we found.”
The research team utilized advanced techniques such as CT scanning, 3D imaging, and electron microscopy to analyze the mummies. Contrary to expectations, they did not find any remnants of soft tissue. Instead, they discovered a thin layer of clay, measuring less than one-hundredth of an inch, that had formed over the skin of the dinosaurs. This clay layer, which retained the molds of the original features, is what led to the misidentification of the specimens as “mummies.”
In discussing the implications, Sereno explained the historical context of the findings, noting that H.F. Osborn, a paleontologist at the American Museum of Natural History, had previously suggested that the features were not actual dehydrated skin. The new study proposes an alternative term—“rendering”—to better describe the clay casts that accurately replicated the dinosaurs’ outer features.
The preservation conditions that led to these remarkable finds stem from the climate of the Late Cretaceous Period, characterized by cyclical droughts and monsoon-like rains. The team hypothesizes that after the dinosaurs died, their carcasses would have dried quickly in sunlight. Subsequently, a flash flood would have buried them in sediment, allowing decay processes to create a film of bacteria that attracted clay particles, forming the precise molds observed today.
Dr. Anthony Martin, a professor at Emory University, commented on the significance of clay in fossilization, stating, “Clay minerals have a way of attracting to and sticking onto biological surfaces, ensuring a molding that can faithfully reproduce the outermost surfaces of a body.” This understanding may also lead to better identification of future fossil finds.
The detailed examinations of the newly unearthed mummies provided insights into the physical appearance of Edmontosaurus. The analyses suggest that these dinosaurs were over 12 meters (40 feet) long, featuring a fleshy crest along their necks and backs, along with rows of spikes down their tails. The clay casts revealed that these creatures had hooves, a trait previously documented only in mammals. This discovery positions Edmontosaurus as the oldest known land animal with hooves, challenging previous assumptions about the evolution of this feature.
In summary, the research published in the journal Science not only clarifies the nature of these unique fossil finds but also opens avenues for further exploration in paleontology. Understanding the processes that led to these extraordinary preservations can guide scientists in their search for additional specimens in the future, potentially enriching the narrative of dinosaur evolution.
