Twenty years ago, near the border between Belgium and the Netherlands, an amateur fossil hunter named Maarten van Dinther picked up a featureless block of rock the size of a pack of cards. Though he didn’t know it at the time, the little slab contained a tiny and perfect skull from the oldest direct relative of modern birds ever discovered, a fowl that walked the Earth with dinosaurs.

The animal, affectionately dubbed the ‘wonderchicken’ by the international team of scientists that analyzed the fossil, lived 66.7 million years ago, just 700,000 years before the asteroid impact that killed off all non-avian dinosaurs. Named Asteriornis in a paper published today in Nature, the species—known from fossils of its hind limbs in