Scientists have debated for years whether dinosaurs were already in decline before a large asteroid hit Earth about 66 million years ago, causing one of the biggest extinction events in history. A new study published in Science suggests that dinosaurs were still thriving in parts of North America just before the asteroid impact. Researchers examined fossils from the Kirtland Formation in northern New Mexico, a site known for its dinosaur remains. By analyzing tiny volcanic glass pieces in sandstone and the magnetic direction of minerals in nearby rocks, they estimated that the fossils were from about 400,000 years before the asteroid strike—very close to the end of the dinosaurs’ era. The fossils include Tyrannosaurus rex, long-necked sauropods, and a horned dinosaur similar to Triceratops, showing that dinosaurs were still diverse and active at the time.

However, experts say the findings from one location may not represent the entire world. Paleontologist Daniel Peppe from Baylor University said dinosaurs in different regions lived in unique communities before the extinction. Other scientists, including Mike Benton from the University of Bristol, said the discovery is important but limited. Because carbon dating cannot be used on fossils this old, scientists use rock-based methods instead. Co-author Andrew Flynn of New Mexico State University added that more studies are needed to understand global dinosaur populations before the asteroid impact.