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聽evolution聽of feathers, like the ones on modern birds, back by 10 million years and may tell us more about why most birds didn鈥檛 survive the post-asteroid mass extinction.
鈥淭his is the best feather we鈥檝e ever seen in a Mesozoic [252 million to 66 million years ago] deposit,鈥� says at the Field Museum in Chicago. 鈥淸It鈥檚] like a feather you could pick up off the ground.鈥�
Birds were the only dinosaurs to survive the mass extinction triggered by an asteroid strike 66 million years ago. But, puzzlingly, only one branch made it through: neornithes, the ancestors of every bird alive today.
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In 2016, at the University of Washington in Seattle was collecting fish fossils in north-eastern Montana鈥檚 Hell Creek Formation when he discovered a broken coprolite, a fossilised dropping, with a feather clearly visible along its fractured surface. 鈥淚 couldn鈥檛 believe what I was seeing,鈥� he says.
A few years later, he invited O鈥機onnor 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.
Further analyses showed that the 9.3-millimetre-long primary feather had a water-repellent structure, similar to that of modern pelicans, says O鈥機onnor. 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.
鈥淲hat is exciting is to push the occurrence of modern feathers into non-modern birds,鈥� says O鈥機onnor. Differences in plumage are emerging as a major contributing factor as to why some birds survived while others didn鈥檛, she says.
The team also found two fluffy body feathers with loosely arranged branches, echoing in a lineage that didn鈥檛 survive the extinction event.
Combined, this suggests that the bird the feather belonged to 鈥� and hesperornithiformes in general 鈥� had a 鈥渕iddle ground鈥� of primitive and modern plumage, says O鈥機onnor. 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 鈥渨inter鈥� that occurred after the asteroid impact.
鈥淭hese are the feathers that are responsible for keeping the body warm, right?鈥� says O鈥機onnor. 鈥淪o 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.鈥�
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The dropping 鈥� which probably came from a Nanotyrannus or a young Tyrannosaurus rex 鈥� 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.
鈥淭his discovery is really exciting,鈥� says at the University of Connecticut. 鈥淚t 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.鈥�
The links among the different animals involved are also fascinating, says Muzio. 鈥淒iscoveries like this really make the imagination run wild,鈥� he says. 鈥淔rom a single coprolite, we are learning about at least three individual species 鈥� morphologically, ecologically and evolutionarily. What more can you ask for?鈥�
Current Biology
Article amended on 11 September 2026
We have updated this article to reflect that the feather was 9.3 millimetres in length.
