A new study challenges the idea that dinosaurs were declining before their extinction 66 million years ago. Researchers found evidence of thriving dinosaur communities in New Mexico right up to the asteroid strike. The findings highlight distinct regional ecosystems shaped by climate.
For decades, scientists believed dinosaurs were fading before the asteroid impact that marked the end of the Cretaceous period 66 million years ago. However, a study published in Science by researchers from Baylor University, New Mexico State University, the Smithsonian Institution, and international partners reveals otherwise. The team analyzed fossils from the Naashoibito Member of the Kirtland Formation in northwestern New Mexico's San Juan Basin, dating them to between 66.4 and 66 million years old—precisely at the Cretaceous-Paleogene boundary.
"The Naashoibito dinosaurs lived at the same time as the famous Hell Creek species in Montana and the Dakotas," said Daniel Peppe, Ph.D., associate professor of geosciences at Baylor University. "They were not in decline—these were vibrant, diverse communities."
The research shows dinosaurs formed distinct "bioprovinces" across North America, primarily influenced by regional temperature differences rather than geographic barriers like mountains or rivers. First author Andrew Flynn, Ph.D., assistant professor of geological sciences at New Mexico State University, emphasized: "What our new research shows is that dinosaurs are not on their way out going into the mass extinction. They're doing great, they're thriving and that the asteroid impact seems to knock them out. This counters a long-held idea that there was this long-term decline in dinosaur diversity leading up to the mass extinction making them more prone to extinction."
Post-impact, ecosystems recovered with mammals diversifying within 300,000 years, adopting new diets, sizes, and roles. Temperature-driven patterns persisted into the Paleocene, with northern and southern mammal communities remaining distinct. "The surviving mammals still retain the same north and south bio provinces," Flynn noted. "Mammals in the north and the south are very different from each other, which is different than other mass extinctions where it seems to be much more uniform."
Conducted on public lands managed by the U.S. Bureau of Land Management, the study underscores life's resilience and vulnerability to sudden catastrophes. The research team included experts like Stephen L. Brusatte from the University of Edinburgh and Alfio Alessandro Chiarenza from University College London, funded by organizations including the National Science Foundation and the European Research Council.