FOSSILGUY.COM

---

Dinosaurs Were Thriving Until the Asteroid Hit, New Mexico Fossils Reveal

A new study reveals dinosaurs in New Mexico's Naashoibito Member were flourishing right up until the asteroid impact 66 million years ago-challenging the idea that they were already dying out.

---

Dinosaurs Were Thriving Until the Asteroid Hit, New Mexico Fossils Reveal

This news article is based on a News Release from NMSU and the Journal Article (Flynn, Andrew G. et al. 2025) from Science

---

Dinosaurs Were Thriving Until the Very End, New Study Finds in New Mexico
For decades, paleontologists have debated whether dinosaurs were already fading before the asteroid struck 66 million years ago-or whether they were abruptly wiped out while still thriving. A new study published in Science led by Andrew Flynn of New Mexico State University offers compelling evidence that dinosaurs were alive and well until the very end.

Flynn and his collaborators from Baylor University, New Mexico Tech, the University of Edinburgh, the Smithsonian Institution, and others examined fossil-bearing rocks in the San Juan Basin of northwestern New Mexico. These fossils, from the Naashoibito Member of the Ojo Alamo Formation in the De-Na-Zin Wilderness, preserve some of the last-known non-avian dinosaurs-the final generations before the mass extinction event that ended the Age of Dinosaurs.

A Southern Counterpart to the Hell Creek Formation
Until recently, much of what scientists knew about the dinosaurs' final days came from the famous Hell Creek Formation, which stretches across parts of Montana, North Dakota, South Dakota, and Wyoming. This northern ecosystem, dominated by Triceratops, Edmontosaurus, and Tyrannosaurus rex, painted a picture of a lush, floodplain world filled with large herbivores and apex predators. However, because nearly all well-dated end-Cretaceous fossils came from this single region, paleontologists couldn't tell whether these faunas represented global conditions or just a northern snapshot.

That's where Flynn's New Mexico research changes the story. Using magnetostratigraphy (which tracks Earth's magnetic field reversals preserved in rock layers) and precise radiometric dating, Flynn's team confirmed that the Naashoibito Member fossils are the same age as those from Hell Creek-right up to the final few hundred thousand years of the Cretaceous. Yet, the New Mexico fossil record tells a very different ecological story.

A Distinct Southern Ecosystem
While Hell Creek's northern plains were filled with duck-billed and horned dinosaurs, New Mexico's landscapes were home to entirely different communities. The enormous sauropod Alamosaurus dominated the south-an immense long-necked herbivore reaching up to 80 tons and standing nearly 50 feet tall. Its presence so late in the Cretaceous surprised scientists when it was first discovered decades ago, and Flynn's study confirms it persisted until the very end.

Alongside Alamosaurus lived a variety of smaller dinosaurs, including predators and herbivores spanning multiple groups. Flynn's team found that these southern ecosystems were diverse, regionally unique, and thriving, not depauperate or in decline. "What our new research shows," Flynn explained, "is that dinosaurs are not on their way out going into the mass extinction. They're doing great-they're thriving."

Dinosaurs Divided by Climate and Geography
By comparing the Naashoibito fauna with those from Hell Creek, the researchers revealed that the Cretaceous world of western North America was divided into distinct bioprovinces. Climate appears to have been a key factor. The southern region-warmer and more arid-supported sauropods like Alamosaurus, while cooler, wetter northern environments favored hadrosaurs and ceratopsians.

This finding challenges older views that the Late Cretaceous featured a uniform, continent-wide ecosystem. Instead, dinosaurs in the final million years of the Cretaceous were living in regionally adapted communities, each shaped by temperature, vegetation, and geography. These results suggest that the dinosaurs' world was more complex and dynamic than previously thought.

Not a Slow Decline, but a Sudden Catastrophe
One of the most striking implications of Flynn's research is that dinosaurs were not in a slow decline before the asteroid impact. Statistical models and fossil diversity analyses show no evidence of dwindling populations or collapsing ecosystems. The Naashoibito dinosaurs, like their Hell Creek counterparts, were part of vibrant, stable ecosystems up until the moment of extinction.

When the asteroid struck the Yucatan Peninsula 66 million years ago, the resulting global firestorms, acid rain, and darkness devastated ecosystems within months. According to University of Edinburgh paleontologist Steve Brusatte, a co-author of the study, "These were the dinosaurs that were greeted by the asteroid. And when we compare them with fossils accurately dated from the same time farther north, we can see they are much different. There clearly were many types of dinosaurs thriving up until that moment the asteroid ended it all."

Life After the Impact
The research also provides insights into what happened next. After the extinction, mammals rapidly diversified-especially in the San Juan Basin, which preserves early Paleogene mammal fossils. Despite the devastation, north-south provincial differences persisted, meaning the extinction didn't completely homogenize Earth's ecosystems. Within just a few hundred thousand years, mammals began radiating into new forms, setting the stage for the modern age of mammals.

A Final Piece of the Puzzle
Flynn's next goal is to locate fossil plants from the Naashoibito Member to reconstruct the vegetation that supported these dinosaurs. "Finding the fossil flora is the last missing step," he said. "We have a good picture of what came after the extinction, but we still don't know exactly what the world looked like just before it happened."

By filling in that gap, scientists hope to understand not only how dinosaurs lived at the end-but also how ecosystems recovered afterward. Together, the Naashoibito and Hell Creek Formations offer a more complete view of the last chapter of the Mesozoic: a world full of life, suddenly cut short.

---

---

Journal Article:
Andrew G. Flynn et al., Late-surviving New Mexican dinosaurs illuminate high end-Cretaceous diversity and provinciality. Science 390, 400-404 (2025). DOI:10.1126/science.adw3282.

---

Recommended Dinosaur Books and Educational Items:

---

High quality Dinosaur teeth by Fossilera

---