Dear Mummy: Rare fossil reveals common dinosaur’s soft tissue

A mummified dinosaur unearthed in Montana a year ago is giving scientists a rare peek at what the creature’s muscles and other soft tissues may have looked like.

The duck-billed animal–dubbed Leonardo by its discoverers–would have been about 7 meters long and weighed about 2 tons when it traipsed around Montana in large herds about 77 million years ago. The most complete mummified dinosaur to be described in 70 years, the fossil includes three-dimensional, mineralized casts of the animal’s right shoulder muscle, throat tissue, and skin. Much of the left side of the dinosaur was relatively flattened, with skin drawn taut against ribs and other bones.

Leonardo, the first reported young adult of a species called Brachylophosaurus canadensis, is more than 90 percent complete, says Nate L. Murphy, curator of paleontology at the Phillips County Museum in Malta, Mont. More than 80 percent of Leonardo’s skin is intact. That made it difficult to decide where to cut the fossil apart during excavation, says Murphy. He and his colleagues ultimately unearthed the find in a single, 6.5-ton block of sandstone.

A piece of fossilized skin that fell from Leonardo’s side while researchers prepared the specimen for exhibition provided a look at the dinosaur’s last meal. Preliminary analyses suggest magnolia and conifer, says Murphy. Pollen and spores in the last meal came from ferns and liverwort, which grow in subtropical environments. Murphy and his colleagues described their find last week at the Society of Vertebrate Paleontology meeting in Norman, Okla.

The presence of liverwort, a plant that can’t survive even a short period of dry conditions, strongly suggests that Leonardo’s mummification didn’t result primarily from desiccation. If the environment was really hot and humid, finding Leonardo would be the equivalent of stumbling across a long-dead but intact elephant in a steamy tropical jungle, says Michael J. Everhart of Fort Hays State University in Hays, Kansas. “Something had to shut down the normal process of decomposition within just a few days,” he notes. “It’s difficult to explain.”

The sediments surrounding Leonardo suggest that when the animal died, it fell onto a sandbar along an ancient river, says Murphy. It’s possible that minerals in the river infiltrated the dinosaur’s soft tissues, preserving them after the animal was buried in the riverbed, he notes.

Whatever happened, the mummification process also preserved a network of tendons and a frill–like a rooster’s comb–that ran along the creature’s back. “Leonardo will be a great test of how scientists have imagined dinosaurs to appear,” Murphy says.

Everhart agrees: “The information locked in this specimen will take years to dig out and interpret.”

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