Exquisite 66-million-year-old bird feather preserved in dinosaur dropping

· New Scientist

A feather preserved in a dinosaur dropping, found in 2016 in north-eastern Montana’s Hell Creek FormationO'Connor et al.

A bird that was eaten and partially excreted by a dinosaur 66 million years ago has left behind the best-preserved feathers ever recovered by scientists from dinosaur-age rock. This pushes the evolution of feathers, like the ones on modern birds, back by 10 million years and may tell us more about why most birds didn’t survive the post-asteroid mass extinction.

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“This is the best feather we’ve ever seen in a Mesozoic [252 million to 66 million years ago] deposit,” says Jingmai O’Connor at the Field Museum in Chicago. “[It’s] like a feather you could pick up off the ground.”

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In 2016, David DeMar, Jr at the University of Washington in Seattle was collecting fish fossils in north-eastern Montana’s Hell Creek Formation when he discovered a broken coprolite, a fossilised dropping, with a feather clearly visible along its fractured surface. “I couldn’t believe what I was seeing,” he says.

A few years later, he invited O’Connor to team up with him and his colleagues to analyse the coprolite using micro-CT scans and 3D surface scanning. Two leg-bone fragments, 18 and 12 millimetres long, resembled some previously found at Hell Creek and attributed to hesperornithiformes. These were flightless, short-winged diving birds, similar to modern loons (Gaviiformes) or grebes (Podicipediformes), and were related to Neornithes.

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Further analyses showed that the 9.3-centimetre-long primary feather had a water-repellent structure, similar to that of modern pelicans, says O’Connor. Both this and a second, smaller wing feather also had lightweight, spongy cores surrounded by a harder outer layer. This combination makes them both light and stiff, which is typical of modern feathers.

“What is exciting is to push the occurrence of modern feathers into non-modern birds,” says O’Connor. Differences in plumage are emerging as a major contributing factor as to why some birds survived while others didn’t, she says.

The team also found two fluffy body feathers with loosely arranged branches, echoing primitive feathers found in 100-million-year-old Myanmar amber in a lineage that didn’t survive the extinction event.

David DeMar, Jr holding the exposed fossil feather in the coprolite fragment in 2016David DeMar, Jr.

Combined, this suggests that the bird the feather belonged to – and hesperornithiformes in general – had a “middle ground” of primitive and modern plumage, says O’Connor. While the wing and tail feathers might have allowed for successful diving, for example, the less advanced body feathers would have been relatively poor insulators, making the animals more vulnerable to the “winter” that occurred after the asteroid impact.

“These are the feathers that are responsible for keeping the body warm, right?” says O’Connor. “So maybe these primitive feathers were good enough to keep them warm during the greenhouse world of the Mesozoic, but not good enough to keep them warm during this environmental catastrophe that was triggered by this impact event.”

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The dropping – which probably came from a Nanotyrannus or a young Tyrannosaurus rex – also contained two rigid, diamond-shaped scales, 3 to 4 millimetres long. The researchers think this came from a gar (Lepisosteidae), a narrow-bodied fish that still exists today. This would have been too small for the dinosaur predator and thus was probably eaten by the bird.

“This discovery is really exciting,” says Frank Muzio at the University of Connecticut. “It opens up so many questions about how feathers evolved, what they were originally used for, and how they came to perform so many different functions in modern birds.”

The links among the different animals involved are also fascinating, says Muzio. “Discoveries like this really make the imagination run wild,” he says. “From a single coprolite, we are learning about at least three individual species – morphologically, ecologically and evolutionarily. What more can you ask for?”

Journal Reference:

Current Biology DOI: 10.1016/j.cub.2026.08.054 

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