Earlier this week scientists studying fossilized teeth from a hadrosaur revealed how the duck-billed dinosaur chewed plants for food. Now another team, analyzing what may be the most intact dinosaur mummy discovered yet, report fresh details about the skin of a hadrosaur nicknamed Dakota, which might have been bigger and moved more quickly than previously thought.

"This is the closest you'll get to touching an extinct dinosaur," says Phillip Manning, a paleontologist at the University of Manchester in England whose team is publishing its findings Wednesday in the Proceedings of the Royal Society B: Biological Sciences.

Paleontologists excavated the fossil from a dusty bluff in the Hell Creek Formation, a rock bed stretching across the Dakotas and Montana that is one of the richest fossil troves known. The stone at Hell Creek dates back to the end of the age of dinosaurs roughly 65 million years ago and was laid down by rivers that flowed eastward through swamps to an inland sea that once ran from Canada to the Gulf of Mexico.

The dinosaur, approximately 7.5 meters (25 feet) long, apparently died on the banks of a sandy channel, perhaps near the bend of a river, where its body was rapidly buried under accumulating sediment. The waterlogged soil entombed it in a mineral-rich soup before the body could decay much, thus ensuring highly detailed preservation. Although fossils containing organic compounds or mummified soft tissues have been discovered before, the presence of both in one find is "as rare as hen's teeth, and the preservation seen in Dakota is something not seen in any other fossil to date," Manning says.

The fossilized soft tissues resemble those seen in modern birds and crocodilians, "additional evidence to the quite obvious links between dinosaurs and birds," Manning says. The pelvis and pectoral bones of the hadrosaur suggest it was an Edmontosaurus, which may have been prey for tyrannosaurs.

Unlike most fossils of dinosaur skin, which just result from scales indenting the sediment around them, the finding here contains actual rust-brown mineralized skin, complete with microscopic cell-like structures between five and 30 microns wide. "I'm amazed at the evidence of actual skin structure preserved in the fossil," remarks vertebrate paleontologist Mike Benton of the University of Bristol in England, who did not participate in this study.

The researchers uncovered an extraordinary amount of skin from the tail, legs and an arm. "When you have skin, you can then begin to figure out what the volume of muscles under it might be," Manning explains. "Although one can use the skeleton to figure out roughly where muscles once attached, when you have a handle on the muscle volume, that can help you calculate muscle energy and how fast or strong a dinosaur was."

The samples in this case suggest that the hadrosaur's backside is some 25 percent larger than once thought, potentially enabling it to run at 45 kilometers per hour (about 28 miles per hour), a bit faster than the top human sprinters. Although the precise color of the skin remains unknown, the data confirm previous evidence that the hadrosaur's skin might have had stripes.

Thanks to its use of electron microscopy, infrared spectroscopy and x-ray analysis, along with a battery of other tests, the team is confident that it is indeed looking at fossilized skin. "There are many past examples of overly optimistic reporting of supposed soft tissues—skin, liver, eyes, heart—in dinosaurs and other fossil vertebrates that remain unconvincing," Benton says. "Phil Manning and his large team have spent the past three years applying every possible kind of modern analytical technology to the dinosaur mummy, and their core claims about the extraordinary envelope of skin around the specimen are confirmed."

The team also reports discovering organic compounds from the mummy that seem to be by-products of protein decay. "These could help us understand more about the process of decay and preservation of biomolecules, which is a bit of a black box right now," Manning says. And further analysis may reveal more secrets about the compounds. As Manning's Manchester colleague Roy Wogelius puts it, "This first result with Dakota is just a beginning."