A Feather Inside a Tyrannosaur's Droppings Is the First Ever Found That Way, and It May Say Why Some Birds Survived

These are the first hesperornithiform feathers ever identified, which is itself remarkable for a group known from skeletons for a century and a half. And they are not all alike. Two have a square shaft with a sponge-like centre, a design found in living birds and, in the fossil record, not seen again until the early Eocene deposits of Denmark, roughly ten million years after the extinction. Others are small, fuzzy and primitive, the kind of body covering associated with non-avian dinosaurs and with the enantiornithines, the dominant birds of the Cretaceous, none of which survived. "Some of these diving birds' feathers seem to have been modern-looking and waterproof," O'Connor says, "but they also had some smaller, fuzzy, primitive body feathers that we associate with dinosaurs."

Why it matters for the extinction

The question that has hung over bird palaeontology for decades is why, when the asteroid struck, only one lineage of birds came through: the one that gave rise to everything from ostriches to sparrows. The enantiornithines, more diverse and in many places more common, vanished with the dinosaurs. So did the hesperornithiforms, for all their modern feathers. Explanations have ranged from diet to habitat to the loss of the forests, and O'Connor's group adds another. "We think the types of feathers that these birds had, and/or the way they moulted those feathers, may have been one of the underlying causes of the selectivity of the end-Cretaceous mass extinction," she says. A bird with a full, modern, insulating coat, and a moult that replaces it in an orderly way, would have been better placed to survive the cold, dark years after the impact than one that was partly fuzz. The hesperornithiforms had some of the kit but not all of it, and they did not make it either.

It is a hypothesis, and a coprolite is a small sample. But it is a sample from the last moment before the catastrophe, from a lineage close to modern birds, and it preserves soft tissue that the Hell Creek bones never do. "It's such a beautiful, well-preserved feather, from such an unexpected source," O'Connor says. "No one has ever thought to look for feathers in coprolites." Eleven researchers from seven institutions, including the Burke Museum in Seattle, where DeMar works, the Carter County Museum in Montana, the University of Colorado Boulder, Beijing's Institute of Vertebrate Paleontology and the Natural History Museum of Los Angeles County, are on the paper.

The lesson for collectors

There are drawers of Hell Creek coprolites in museums across North America, catalogued as curiosities and rarely sectioned. The obvious next step is to scan them. If the first one anyone looked at properly had a feather in it, the odds that it is the only one are not good. It is the same lesson we drew from Hubble's Saturn archive last week: the discovery was sitting in the collection, waiting for somebody to ask the question. Full paper: O'Connor et al., "Bird feathers from a Late Cretaceous coprolite", Current Biology, 10 September 2026.