A fossil feather from the age of dinosaurs may explain why only some birds survived

David DeMar Discovers Rare Hell Creek Coprolite

Paleontology is rarely a tidy discipline. Back in 2016, David DeMar was doing field work in the rocky badlands of Montana within the Hell Creek Formation, a geologic unit heavily studied by museum teams for more than 110-plus years. While crawling up a rocky outcrop to collect fish fossils, the Burke Museum lab manager spotted a dark, reddish-brown nodule about half the size of a golf ball.

After picking up the cherry-sized fossil, DeMar scanned its surface through a hand lens. I start looking at the surface of it, he says. And then I rolled it over and I was like, 'You got to be kidding me.' Embedded in a small surface crack was a tiny, pristine fossilized branching structure. He quickly radioed his colleagues on a walkie-talkie, though initial responses were skeptical. They probably thought I was kidding, DeMar said. But I got back on the walkie about five minutes later. I was like, 'No, hey guys, I think I found a bird feather.'

Jingmai O’Connor and CT Scan Reveal Dinosaur Food Web Secrets

Subsequent analysis confirmed the discovery, which dates back to the late Cretaceous right before the catastrophic asteroid impact wiped out the dinosaurs and a large swath of other species. When Jingmai O’Connor joined the project, the primary objective was determining which animal the feather belonged to and what it could reveal about evolutionary history. The round object containing the specimen turned out to be a coprolite—fossilized feces—produced by a large meat-eating dinosaur. Based on the size and contents of the coprolite, Tyrannosaurus rex or Nanotyrannus emerge as the most likely candidates. This coprolite had actually broken off from a few larger, softball-sized pieces where additional clues may later be found.

Micro-CT scanning revealed that the coprolite contained much more than a single plume. Researchers found multiple feathers, tiny fish scales, and bone fragments from a small bird packed tightly inside the fossilized faeces. Because large theropods typically did not consume fish, the research team concluded that the scales belonged to the bird’s last meal before it was eaten by a predator, capturing two distinct food web interactions in a single specimen.

Jingmai O’Connor, Field Museum of Natural History

It is, without a doubt, the best feather we've ever found from the age of dinosaurs, says Jingmai O’Connor, a bird expert and an associate curator of fossil reptiles at the Field Museum of Natural History in Chicago. Dr O’Connor noted that coprolites are potentially a new window through which we can study fossilised soft tissues.

The exceptional preservation has stunned specialists outside the immediate research team. Steven Salisbury, a vertebrate palaeontologist at the University of Queensland, noted that while other fossils show impressions of feathers, most of the time you're just looking at impressions of feathers… the actual feather is not there. This is cool because it's actually the preserved feather in 3D, Dr Salisbury said. Richard Prum, an ornithologist at Yale University who did not contribute to the research, called the discovery remarkable, unexpected, noting that there's nothing of that age that's so beautifully preserved, [including] evidence of individual cells.

Hesperornithiforms and the Cretaceous Extinction Mystery

The feather itself is believed to belong to a hesperornithiform, an ancient aquatic, foot-propelled diving bird comparable to a modern loon or grebe. While these diving birds were closely related to modern crown birds, O’Connor points out that hesperornithiformes do not have the full suite of modern plumage characteristics. According to Dr. O’Connor, plumage might have been the difference between life and death during the extinction event, as researchers can hypothesize that only crown birds had the full suite of body feathers good for insulation plus modern wing feathers, helping them survive while ancient diving birds and dinosaurs perished.