The most iconic mass extinction in Earth's history occurred about 66 million years ago, when rapid environmental destruction led to the extinction of about 75% of species, most notably non-avian dinosaurs, and a subsequent restructuring of terrestrial ecosystems. The debate is whether dinosaurs suddenly disappeared after being diverse and thriving, or whether they suffered a long-term decline until the end of the Cretaceous.
Flynn etc.. analyzed Alamosaurus the fossils found in northwestern New Mexico that revealed these dinosaurs were very different, but the same age as the dinosaurs found further north in Wyoming and Montana. Image credit: Natalya Yagelskaya.
In northwestern New Mexico, rock layers hold a hidden chapter of Earth's history.
In the Naashoibito Formation of the Kirtland Formation, Baylor University paleontologist Daniel Peppe and his colleagues found evidence of vibrant dinosaur ecosystems that flourished right up until the asteroid impact.
High-precision dating methods have shown that fossils from these rocks are between 66.4 and 66 million years old.
“The Naashoibito dinosaurs lived at the same time as the famous Hell Creek species in Montana and the Dakotas,” Dr. Peppe said.
“They weren’t in decline—they were vibrant, diverse communities.”
New Mexico fossils tell a different story than originally thought.
Dinosaur communities throughout North America were not homogeneous or weakened, but regionally distinct and thriving.
Using ecological and biogeographic analysis, the researchers found that dinosaurs in western North America lived in distinct bioprovinces, separated not by mountains or rivers but by temperature differences between regions.
“Our new study shows that dinosaurs are not on a path to mass extinction,” said New Mexico State University researcher Andrew Flynn.
“They're doing great, they're thriving, and the asteroid strike seems to have knocked them out.”
“This contradicts the long-standing idea that there was a long-term decline in dinosaur diversity that led to the mass extinction, making them more likely to go extinct.”
“The asteroid impact ended the age of the dinosaurs instantly, but the ecosystems they left behind set the stage for what came next.”
“300,000 years after the extinction, mammals began to diversify rapidly, exploring new diets, body sizes, and ecological roles.”
“The same temperature patterns that shaped dinosaur communities persisted into the Paleocene, showing how climate helped life recover after disaster.”
“The surviving mammals still maintain the same northern and southern bioprovinces.”
“Mammals in the north and south are very different from each other, which is different from other mass extinctions where it appears to be much more homogeneous.”
conclusions appear in the magazine today Science.
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Andrew J. Flynn etc.. 2025. Late survivors of New Mexico dinosaurs shed light on diversity and provinciality of the High Late Cretaceous. Science 390 (6771): 400-404; doi: 10.1126/science.adw3282
