Picture a warm floodplain filled with giant duck-billed dinosaurs, horned triceratops, and enormous long-necked Alamosaurus moving through dense forests. This was New Mexico about 66 million years ago. Life was rich, ecosystems were thriving, and the land was alive with sound and color. Then, suddenly, everything changed. A massive asteroid slammed into Earth and ended the reign of the dinosaurs. But before that impact, these ancient giants were far from dying out.
A new study published in Science reveals that dinosaurs in New Mexico were alive and thriving until the very end of the Cretaceous period. They weren’t fading away slowly; they were flourishing in one of the last strongholds of dinosaur life on the planet.
Fast Facts
- Study Focus: Late Cretaceous dinosaur fossils from the Naashoibito Member, San Juan Basin, New Mexico.
- Discovery: Dinosaurs like Alamosaurus were thriving until the asteroid impact 66 million years ago.
- Key Finding: Evidence shows diverse dinosaur “bioprovinces” shaped by temperature, not geography.
- Institutions: Baylor University, New Mexico State University, Smithsonian Institution, and partners worldwide.
- Journal: Published in Science (2025), DOI: 10.1126/science.adw3282.
Scientists Revisit the Rocks of New Mexico
The groundbreaking research was led by Andrew G. Flynn of New Mexico State University, with collaborators from Baylor University, The Smithsonian Institution, University College London, The University of Edinburgh, and several other global partners. The team focused on the Naashoibito Member of the Kirtland Formation in the San Juan Basin, northwestern New Mexico.
For years, scientists debated how old these rocks were. Some believed they belonged to an earlier chapter of dinosaur history, millions of years before extinction. Others suspected they held the very last traces of dinosaur life.
Using advanced radiometric dating and magnetostratigraphy, the team discovered that the Naashoibito layer formed between 66.4 and 66.0 million years ago, just a few hundred thousand years before the asteroid impact. That means the fossils found there, including Alamosaurus, were among the last dinosaurs on Earth.
These fossils showed remarkable diversity: duck-billed hadrosaurs, horned ceratopsians, and sauropods like Alamosaurus. Their presence paints a picture of a lively, balanced ecosystem filled with both giants and smaller species. Far from declining, the dinosaurs of New Mexico were thriving right until the final moments before the impact.
“There is no sign that these dinosaurs were in any trouble, or that anything unusual was happening to them, or that they were in any type of long-term decline.” — Stephen L. Brusatte, University of Edinburgh
Why This Discovery Changes the Dinosaur Story
For over a century, scientists believed dinosaurs were already declining before the asteroid struck. Evidence from the northern United States, especially Montana’s Hell Creek Formation, seemed to suggest that fewer species existed in the last million years of the Cretaceous.
This new research overturns that idea.
“They were doing great, they were thriving, and the asteroid impact seems to knock them out. This counters a long-held idea that there was a long-term decline leading up to extinction.” — Andrew G. Flynn, New Mexico State University
“The Naashoibito dinosaurs lived at the same time as the famous Hell Creek species in Montana and the Dakotas. They were not in decline; these were vibrant, diverse communities.” — Daniel J. Peppe, Baylor University
The findings prove that southern and northern dinosaurs lived simultaneously and were equally successful until the very end. The extinction was not a gradual fade; it was a sudden, catastrophic event that ended a thriving era.
Life in the San Juan Basin
Sixty-six million years ago, the San Juan Basin was a lush landscape of rivers, forests, and wetlands, not the arid desert we see today. Dinosaurs like Alamosaurus towered over the plains, while duck-billed hadrosaurs grazed and horned species defended their herds. The air was warm, and plant life thrived.
The fossils from this region reveal something deeper than simple survival. Researchers discovered that dinosaur populations were divided into distinct regional communities, or “bioprovinces.” These bioprovinces weren’t shaped by mountains or rivers but by temperature. In warmer regions like New Mexico, certain species thrived, while cooler northern climates hosted different kinds of dinosaurs.
This pattern of temperature-driven ecosystems didn’t end with the dinosaurs. After the extinction, mammals in the early Paleocene also formed distinct northern and southern bioprovinces, showing that climate continued to shape life’s recovery long after the asteroid impact.
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Explore the DiscoveryDinosaurs Were Thriving Until the Final Blow
The Naashoibito fossils prove that dinosaurs were evolving and diversifying up to the very end. There was no sign of decline. Instead, regional ecosystems remained strong and full of life.
Then, everything changed. About 66 million years ago, an asteroid struck what is now Mexico’s Yucatán Peninsula. Within hours, fires raged, skies darkened, and temperatures plummeted. Seventy-five percent of Earth’s species vanished, including every non-bird dinosaur.
The dinosaurs of New Mexico, once surrounded by rivers and forests, were buried in the chaos. Their world ended not because they were weak but because the planet itself changed in an instant.
How Life Rebounded After the Fall
In the aftermath of destruction, life found a way to begin again. Within 300,000 years, mammals began to diversify rapidly. Fossils from the nearby Nacimiento Formation show how small mammals developed new diets, sizes, and ecological roles to fill the empty spaces left by dinosaurs.
Interestingly, the same temperature-based regional patterns that shaped dinosaur ecosystems also guided how mammals evolved after the impact. Northern and southern communities stayed distinct for hundreds of thousands of years. Life was adapting, but climate remained a key driver of diversity.
“The surviving mammals still retain the same north and south bio provinces. Mammals in the north and the south are very different from each other.” — Andrew G. Flynn, New Mexico State University
The Role of Public Lands and Collaboration
This remarkable discovery was made on public lands managed by the U.S. Bureau of Land Management (BLM). The researchers thanked the BLM for providing collecting permits and supporting their work. It’s a powerful example of how protected landscapes help unlock scientific discoveries, preserving clues to life’s greatest stories hidden in stone.
The study also represents a global collaboration across institutions and continents. Scientists from the United States, the United Kingdom, Spain, and beyond combined geology, ecology, and paleontology to build one of the clearest pictures yet of the dinosaurs’ final days.
Why This Discovery Matters Today
The study’s implications reach far beyond prehistory. It reminds us that climate, resilience, and chance play powerful roles in the fate of life. Dinosaurs weren’t defeated by weakness but by an unexpected disaster from beyond the sky. Their story echoes the balance of fragility and adaptability that continues to shape ecosystems today.
“The fossils of New Mexico are telling us that life was thriving here right up to the end. The asteroid was the real killer, not a long, slow decline.” — Thomas E. Williamson, New Mexico Museum of Natural History
From vibrant dinosaurs to fast-evolving mammals, the record in New Mexico captures both life’s endurance and its vulnerability, a timeless lesson about how quickly a thriving world can change.
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Explore FurtherFAQs
The fossils from New Mexico’s Naashoibito Member are among the youngest ever found, dating to just before the asteroid impact 66 million years ago. Unlike other sites that show signs of ecosystem decline, these fossils reveal that dinosaurs like Alamosaurus, Triceratops, and hadrosaurs were still thriving. This challenges the long-standing belief that dinosaurs were fading out before the mass extinction.
Researchers used advanced radiometric dating and magnetostratigraphy to pinpoint the age of the rock layers containing the fossils. Their findings show the fossils formed between 66.4 and 66.0 million years ago, just a few hundred thousand years before the asteroid struck. This precise dating confirms that these were some of the last dinosaurs on Earth.
The San Juan Basin preserves a rare record of both the last dinosaurs and the first mammals after the extinction. It shows how climate shaped “bioprovinces”, distinct northern and southern ecosystems driven by temperature differences. These same climate-driven patterns continued into the early age of mammals, revealing how life’s resilience and diversity were tied to environmental change.
Study Reference
Andrew G. Flynn, Stephen L. Brusatte, Alfio Alessandro Chiarenza, Jorge García-Girón, Adam J. Davis, C. Will Fenley, Caitlin E. Leslie, Ross Secord, Sarah Shelley, Anne Weil, Matthew T. Heizler, Thomas E. Williamson, Daniel J. Peppe.
Late-surviving New Mexican dinosaurs illuminate high end-Cretaceous diversity and provinciality.
Science, 2025; 390 (6771): 400. DOI: 10.1126/science.adw3282.
Funding Acknowledgment
This research was supported by the National Science Foundation, European Research Council, Royal Newton International Fellowship, Geologic Society of America, European Union NextGenerationEU Program, British Ecological Society, and the American Chemical Society–Petroleum Research Fund, with additional fieldwork support from Baylor University and the Bureau of Land Management.
