Researchers have identified the best-preserved fossil feathers from the Mesozoic era inside a coprolite—fossilized dinosaur dung—discovered in Montana’s Hell Creek Formation in 2016. The find, which includes ancient bird remains, offers new clues about why some species survived the mass extinction 66 million years ago while others perished.
A Fortuitous Discovery in the Hell Creek Formation
In 2016, while prospecting for fish fossils in the badlands of eastern Montana, researchers from the University of Washington stumbled upon a reddish-brown nodule roughly half the size of a golf ball. David DeMar Jr., a research scientist in the biology department and the Hell Creek Project collections manager at the Burke Museum, initially found the specimen while scaling a rocky slope.
The discovery was serendipitous. A lucky break
on the surface of the coprolite exposed a single feather, which signaled to the team that more could be preserved within. I picked it up and scanned its surface through my hand lens, and that’s when I couldn’t believe what I was seeing: a tiny fossil feather,
DeMar said. I was cautiously optimistic about its discovery, because feathers had not yet been found in the Hell Creek Formation, even after more than 100 years of prospecting.
CT Scanning Reveals 3D Preservation
Once back in the laboratory, the team utilized micro-CT scanning to digitally stack thousands of X-rays, creating a three-dimensional map of the specimen’s interior. The process revealed that the dung was packed with more than just a single feather; it contained multiple feathers, tiny gar fish scales, and leg bones belonging to a hesperornithiform—an extinct aquatic bird group ecologically similar to modern loons.
Nathan Carroll, a paleontologist at the Carter County Museum, described the process of analyzing the data: Every hour processing the data revealed another feather, another scale, another bone — in stunning 3D.
The researchers noted that these feathers survived the digestive process because they were composed of durable keratin, which the dinosaur’s fast-moving digestive system could not fully break down. Two of the feathers exhibited features previously associated only with modern birds and their immediate ancestors, including a square feather shaft with a sponge-like center. According to DeMar, this specific combination of features is unique among known Mesozoic feathers, with the next oldest record appearing in the early Eocene of Denmark—a period roughly 10 million years younger than the Hell Creek specimen.
Clues to Survival During the K-Pg Mass Extinction
The finding provides a potential explanation for why some birds survived the asteroid impact 66 million years ago while others, like the hesperornithiforms, went extinct. While some of the feathers found in the coprolite were modern-looking and waterproof, others were primitive and stringy. Jingmai O’Connor, associate curator of fossil reptiles at the Field Museum of Natural History in Chicago, suggests that poor insulation from these primitive, fuzzy feathers may have hindered the birds’ ability to retain body heat during the cold, dark years following the asteroid strike.
The researchers believe that the specific plumage characteristics of different bird groups may have been a more decisive factor in their survival. As O’Connor noted, That’s something we’re seeing for the first time in the Age of the Dinosaurs.
The study, published September 10 in Current Biology, highlights the untapped potential of coprolites as guardians of ancient biological data. With the success of this project, O’Connor remarked that people should start looking.