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<\/p>\nIn the badlands of eastern Wyoming, the Lance Formation is a trove of prehistoric fossils. And one area in particular \u2014 a region less than 10 kilometers (6 miles) across \u2014 has provided scientists with at least half a dozen remarkably well-preserved dinosaur specimens complete with details of scaly skin, hooves and spikes.<\/p>\n
The paleontologist Dr. Paul Sereno and his colleagues dub it \u201cthe mummy zone\u201d in a new study that aims to explain why this particular area has given rise to so many amazing finds and define exactly what a dinosaur \u201cmummy\u201d is.<\/p>\n
In the early 1900s, a fossil hunter named Charles Sternberg found two specimens of a large duck-billed dinosaur, Edmontosaurus annectens, in the Lance Formation. The skeletons were so pristine that Sternberg, along with H.F. Osborn, a paleontologist at New York\u2019s American Museum of Natural History, could make out what appeared to be large swaths of skin with discernible scales and a fleshy crest that seemed to run along the reptile\u2019s neck.<\/p>\n
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Lead study author Paul Sereno of the University of Chicago marvels at the preserved hooves on the foot of an adult mummy of Edmontosaurus. – Kieth Ladzinski<\/p>\n
Sereno, lead study author and a professor of organismal biology and anatomy at the University of Chicago, described the initial discovery as \u201cthe greatest dinosaur mummy \u2014 until maybe the juvenile that we found\u201d in the year 2000.<\/p>\n
Separated by nearly a century, Sereno and his team\u2019s find shared common traits with Sternberg\u2019s: The skeletons were preserved in three-dimensional poses and showed clear evidence of skin and other attributes that don\u2019t usually survive 66 million years in the ground. \u201cOsborn said in 1912 he knew that it wasn\u2019t actual, dehydrated skin, like in Egyptian mummies,\u201d Sereno said. \u201cBut what was it?\u201d<\/p>\n
Whatever it was, \u201cwe actually didn\u2019t know how it was preserved,\u201d he said. \u201cIt was a mystery.\u201d<\/p>\n
The new research puts that mystery to rest and can help paleontologists find, recognize and analyze future mummy finds for tiny clues into how giant dinosaurs really looked.<\/p>\n
A dinosaur death cast in clay<\/p>\n
Sereno and his collaborators used CT scanning, 3D imaging, electron microscopy and X-ray spectroscopy to analyze two Edmontosaurus mummies they discovered in the Lance Formation in 2000 and 2001 \u2014 a juvenile and a young adult. \u201cWe looked and we looked and we looked, we sampled and we tested, and we didn\u2019t find any\u201d remnants of soft tissue, Sereno said.<\/p>\n
What the team found instead was a thin layer of clay, less than one-hundredth of an inch thick, which had formed on top of the animals\u2019 skin. \u201cIt\u2019s so real-looking, it\u2019s unbelievable,\u201d he said.<\/p>\n
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A thin layer of clay over the fossilized skeleton of the juvenile Edmontosaurus preserved large areas of scaly, wrinkled skin and a fleshy crest over its back. – Tyler Keillor\/Fossil Lab<\/p>\n
Whereas Sternberg and Osborn referred to the \u201cimpression\u201d of skin in their specimens, Sereno\u2019s paper proposes an alternate term \u2014 \u201crendering\u201d \u2014 which he argues is more precise.<\/p>\n
The study lays out the conditions that would produce such a rendering. In the Late Cretaceous Period, when Edmontosaurus roamed what is now the American West, the climate cycled between drought and monsoon rains. Drought has been determined to have been the cause of death of the original mummy found by Sternberg and described by Osborn, and of other animals whose fossils were found nearby. Assuming the same is true of the new specimens, the carcasses would have dried in the sun in a week or two.<\/p>\n
Then, a flash flood buried the bodies in sediment. The decaying carcasses would have been covered by a film of bacteria, which can electrostatically attract clay found in the surrounding sediment. The wafer-thin coating of clay remained long after the underlying tissues decayed completely, retaining their detailed morphology and forming a perfect clay mask.<\/p>\n
\u201cClay 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, such as skin and other soft tissues,\u201d said Dr. Anthony Martin, professor of practice in the department of environmental sciences at Emory University in Atlanta, who was not involved in the research. \u201cSo it makes sense that these clays would have formed such fine portraits of dinosaurs\u2019 scales, spikes and hooves.\u201d<\/p>\n
Dr. Stephanie Drumheller-Horton, a vertebrate paleontologist at the University of Tennessee, Knoxville, who also was not involved in the study, is an expert in taphonomy, which she described as \u201cthe study of everything that happens to an organism from when it dies until when we find it.\u201d She is particularly interested in how these fossils formed.<\/p>\n
\u201cDinosaur mummies have been known for over one hundred years, but there has definitely been more emphasis on describing their skin and less on understanding how they fossilized in the first place,\u201d she said via email. \u201cIf we can understand how and why these fossils form, we can better target where to look to potentially find more of them.\u201d<\/p>\n
A detailed portrait of a duck-billed dinosaur<\/p>\n
Together, the two more recently unearthed mummies allowed Sereno and his team to create a detailed update of what Edmontosaurus probably looked like.<\/p>\n
According to their analyses, the dinosaur, which could grow to over 12 meters (40 feet) long, had a fleshy crest along the neck and back and a row of spikes running down the tail. The creature\u2019s skin was thin enough to produce delicate wrinkles over the rib cage and was dotted with small, pebble-like scales.<\/p>\n
The clay mask revealed that the animal had hooves, a trait previously preserved only in mammals. That makes it the oldest land animal proven to have hooves and the first known example of a hooved reptile, Sereno said. \u201cSorry, mammals, you didn\u2019t invent it,\u201d he joked. \u201cDid we suspect it? Yeah, we suspected it had a hoof from the footprints, but seeing it is believing.\u201d<\/p>\n
The study was published Thursday in the journal Science.<\/a><\/p>\n Amanda Schupak is a science and health journalist in New York City.<\/p>\n