Duck-billed dinosaur fleshy midline and hooves reveal terrestrial clay-template "mummification".

Two "mummies" of the end-Cretaceous duck-billed dinosaur Edmontosaurus annectens preserve a fleshy crest over the neck and trunk, an interdigitating spike row over the hips and tail, and hooves capping the toes of the hind feet. A battery of tests showed that all of the fossilized integument (skin, spike, and hoof) are preserved as a thin (less than 1 millimeter) clay template that formed on the surface of a buried carcass during decay before the loss of all soft tissues and organic compounds. Unlike the underlying permineralized skeletal bone, the integument renderings of these "dinosaur mummies" are preserved as a thin external clay mask, a templating process documented previously only in anoxic marine settings. Editor's summary: A hundred years ago at a site in Wyoming, a seemingly mummified dinosaur was discovered. Since that time, other sites have revealed extraordinarily preserved features of early organisms, such as integument and feathers. The majority of these sites occur in regions where conditions were anoxic and wet, but the Wyoming site was entirely different, being decay prone, oxygenated, and influenced by both drought and floods. Sereno et al. describe two additional duck-billed dinosaur "mummies" from this site for which incredible detail was preserved, including a crest, a row of spikes, and hooves. The authors were also able to identify the taphonomic process that preserved these features in this unexpected climate. —Sacha Vignieri INTRODUCTION: Called dinosaur "mummies," two skeletons of the duck-billed dinosaur Edmontosaurus were discovered in Wyoming more than a century ago preserved like sun-dried carcasses. The snout of one is covered with a ducklike bill, and both have large areas of scaly integument described as "skin impressions." Revisiting this area uncovered a "mummy zone," with finds including two additional Edmontosaurus mummies and exceptional specimens of the contemporaries Triceratops and Tyrannosaurus. How soft tissues fossilize, and whether any of the original organic materials survive, remain open questions. RATIONALE: To investigate integument fossilization, we used high-resolution imaging, thin-section microscopy, and geochemical analyses, documenting the surrounding sediment and the structure and composition of the integument layer. Based on past research, fossilized integument (or "integument rendering") is generated through one of four pathways: cast-vestige, mold, template, or impression. Because terms for integument structures such as "crest" or "hoof" are often used informally, we provide definitions for all major keratinous, cornified structures in tetrapods, dividing those that are entirely fleshy from those underlain by bone. We also compile and organize terms for reptilian scalation under five categories: shape, form, ornamentation, topology, and pattern. RESULTS: The new mummies provide a complete fleshy profile for a large-bodied dinosaur. A fleshy neck-to-trunk crest transitions over the hips into an interdigitating spike row that continues to the tip of the tail. The scales on the crest and trunk are very small for a 12-m reptile, with most measuring 1 to 4 mm in diameter. Wedge-shaped hooves, here preserved in a reptile, cap the toes of fore and hind feet. All soft tissue structures are preserved as a very thin (0.5 mm or less) clay layer or template. Experiments have shown that a biofilm on the surface of decaying tissue can accumulate template clay from surrounding sediment before soft tissue degradation. We found no trace of internal integument structure or original organic material. CONCLUSION: Recently discovered duck-billed dinosaur mummies suggest that "mummification" occurred after drought-induced mortality involving four stages: carcass desiccation and initial subaerial decay, sudden burial with minimal transport, rapid carcass infilling, and templating in clay and final decay. The cyclic drought-flood monsoonal climate of the Lance Formation and its extraordinary thickness under the mummy zone provided the environmental and geologic conditions, respectively, for rapid burial of desiccated, unscavenged carcasses without sediment reworking. Unlike the underlying permineralized skeletal bone, the integument renderings of these dinosaur mummies congealed early in the process of fossilization as a thin external clay mask, a templating process documented previously only in anoxic marine settings. Dinosaur mummies unmasked.: Mummies of the duck-billed dinosaur Edmontosaurus annectens (1) document with a thin external clay template a fleshy crest over neck and trunk (2), a fleshy spike row over hips and tail (3), and hooves capping the toes of the hind feet (4). Preserved as desiccated carcasses (5) and rapidly buried rapidly by floodwaters (6) on a coastline (7), the duck-billed mummies come from the very end of the dinosaur era in what today is east-central Wyoming. [Artwork by Dani Navarro.] [ABSTRACT FROM AUTHOR]