Scientists have long debated whether dinosaurs were already in decline before a massive asteroid struck Earth about 66 million years ago, triggering one of history’s most significant extinction events. A recent study, published in Science, suggests that dinosaurs were still thriving in parts of North America before the impact. Researchers analyzed fossils from the Kirtland Formation in northern New Mexico, a site known for more than a century to contain remarkable dinosaur remains. By examining tiny volcanic glass particles in sandstone and studying magnetic minerals in surrounding rocks, scientists determined the fossils date to roughly 400,000 years before the asteroid collision—an extremely short interval in geological terms. The fossils include species such as Tyrannosaurus rex, long-necked sauropods, and a horned herbivore similar to Triceratops, showing that dinosaurs remained diverse until the end of the Cretaceous Period.

Experts note, however, that findings from a single site cannot represent the entire global picture. Paleontologist Daniel Peppe from Baylor University explained that dinosaurs in different regions formed distinct communities before their sudden extinction. Independent researchers like Mike Benton from the University of Bristol praised the discovery but cautioned that it reflects only one area’s ecosystem. Because materials used in traditional carbon dating cannot survive in fossils this old, scientists rely on rock-based dating methods to determine ages more precisely. Co-author Andrew Flynn of New Mexico State University said that additional studies across multiple sites are needed to understand how dinosaur populations varied worldwide just before the catastrophic impact that reshaped Earth’s history.