In 2016, researcher David DeMar Jr. discovered a 66-million-year-old fossilized dinosaur coprolite in Montana’s Hell Creek Formation containing exceptionally preserved 3D feathers and bones. According to a study published in Current Biology, this rare find offers fresh clues into why certain ancestral bird lineages survived the asteroid-driven mass extinction while others perished.
Unearthing Micro-Details in Montana’s Hell Creek Formation
Field research often demands looking in unexpected places. While crawling up a rocky outcrop in northeastern Montana to search for fish fossils, David DeMar Jr., a research scientist at the University of Washington’s Burke Museum, collected a small, reddish-brown lump. Using a hand lens on the surface of the specimen, he spotted a tiny feather.
That specimen turned out to be fossilized feces, or a coprolite, originating from a predator such as a T. rex or Nanotyrannus. Inside this ancient waste, researchers uncovered feathers preserved in three dimensions alongside gar fish scales and leg bones.
Paleontologist Nate Carroll, who had previously studied amber-trapped feathers from Myanmar for his thesis, helped analyze the object. The research team utilized a micro-CT scanner to peer inside the matrix. “Every hour processing the data revealed another feather, another scale, another bone — in stunning 3D,” Carroll noted in a press release.
DeMar highlighted the rarity of the find. “I was cautiously optimistic about its discovery, because feathers had not yet been found in the Hell Creek Formation, even after more than 150 years of prospecting,” he stated.
Anatomy of an Extinction: Why Some Birds Survived
The leg bones embedded in the coprolite belonged to an extinct diving bird known as a hesperornithiform, which served as the likely source of the feathers. Most hesperornithiforms could not fly and instead relied on their feet to dive for food in aquatic environments, much like modern loons.
Lead author Jingmai O’Connor has dedicated years to investigating why the ancestors of modern living birds survived the mass extinction while other avian groups died out. Previous hypotheses suggested that living near water protected certain species from the immediate devastation of the asteroid impact. However, because hesperornithiforms also lived around water and went completely extinct, an aquatic habitat alone cannot explain the survival divide.
The newly analyzed fossil provided researchers with a direct look at the feathers of these non-surviving aquatic birds. “Some of these diving birds’ feathers seem to have been modern-looking and waterproof, but they also had some smaller, fuzzy, primitive body feathers that we associate with dinosaurs and enantiornithines,” O’Connor explained. Those smaller, primitive feathers likely provided less insulation than the body feathers found in the lineage that gave rise to every bird alive today.
Thermal Insulation and the Post-Impact Winter
Following the asteroid impact, cold conditions during the winter would have made staying warm a challenge. Birds equipped with feathers capable of trapping greater amounts of body heat were better positioned to endure the drop in global temperatures.
While the ancestors of modern birds successfully navigated this thermal bottleneck, enantiornithines and hesperornithiforms—which shared similar primitive feather structures—succumbed to the cold. By bridging macro-evolutionary patterns with microscopic fossil evidence, this 66-million-year-old coprolite gives modern paleontologists a sharper window into the biological traits that mattered most during Earth’s climate test.
