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. But, puzzlingly, only one branch made it through: neornithes, the ancestors of every bird alive today.
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. 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. 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. 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.
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. 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. What more can you ask for?” Current Biology DOI: 10.1016/j.cub.2026.08.054
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