Final days of dinosaurs: What life was like before extinction

New evidence from northwestern New Mexico shows that dinosaurs were still diverse and abundant just before the asteroid hit 66 million years ago.

Their communities weren’t weakening or becoming uniform – they were lively, regionally distinct, and shaped by temperature differences across the landscape.

The work brings together researchers from Baylor University, New Mexico State University, and the Smithsonian Institution.

By pairing high-precision dating with ecological and biogeographic analyses, the study reframes the dinosaurs’ final chapter as a flourishing finish rather than a slow fade.

Dinosaurs’ vibrant final days

In the San Juan Basin, rocks of the Naashoibito Member in the Kirtland Formation capture a narrow window at the very end of the Cretaceous.

Those layers, tucked just below the catastrophe, preserve bones, teeth, and fragments from animals that were alive in the final few hundred thousand years before impact.

Dating puts the fossils between 66.4 and 66.0 million years old, bracketing them within the events 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, an  associate professor of geosciences at Baylor University. “They were not in decline – these were vibrant, diverse communities.”

Thriving until the end

The New Mexico record lines up with other late Cretaceous sites. It reveals something easy to miss when looking only at one region.

The dividing lines weren’t dramatic mountain chains or rivers. They were temperature gradients. Warmer and cooler zones fostered different mixes of herbivores and predators.

These contrasts produced mosaics of communities that thrived in parallel, not a single, uniform biota limping toward extinction.

“What our new research shows is that dinosaurs are not on their way out going into the mass extinction,” said first author Andrew Flynn, an assistant professor of geological sciences at New Mexico State University.

“They’re doing great, they’re thriving and 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.”

Tracing the countdown to impact

High-precision age data form the backbone of the case. The team used careful stratigraphy and state-of-the-art dating methods to anchor the Naashoibito fossils within the final 400,000 years of the Cretaceous.

That timing matters. If dinosaurs had already been dwindling, you’d expect thinning assemblages or homogenized faunas in these layers.

Instead, the fossils point to robust ecosystems with region-specific casts. Hadrosaurs and ceratopsians share space with unique predators and smaller vertebrates that fit local climates.

Climate shaped everything

Temperature emerges as the quiet architect behind these patterns. Subtle shifts in climate carved ecological lanes, and dinosaurs appear to have filled those lanes with ease.

That climate signal persisted across the boundary into the Paleocene, hinting that the rules of ecological assembly didn’t evaporate with the dinosaurs – they bent, then reasserted themselves as life reorganized.

“The surviving mammals still retain the same north and south bio provinces,” Flynn said. “Mammals in the north and the south are very different from each other, which is different from other mass extinctions where it seems to be much more uniform.”

Mammals inherit the Earth

The impact ended dinosaur dominance in a geological instant. Yet the ecological scaffolding they left behind – soils, food webs, climate gradients – helped shape what followed.

Within about 300,000 years, mammals sprinted into vacant niches, experimenting with new diets, body sizes, and lifestyles.

The same temperature-driven bioprovinces that structured late dinosaur ecosystems also shaped early mammal evolution. This pattern suggests that climate kept sorting winners and losers as life rebounded.

Dinosaurs weren’t fading yet

For decades, a popular idea held that dinosaurs were already on a long slide, making them easier targets for extinction. This study flips that script. It shows thriving, not waning; regional variety, not sameness.

That distinction matters because it shifts the emphasis from internal weakness to external catastrophe. The asteroid didn’t nudge a teetering system. It blindsided a dynamic, well-populated world.

There’s also a practical lesson in where these answers come from. Much of the evidence lies on public lands managed by the U.S. Bureau of Land Management.

Careful protection, patient mapping, and open collaboration allowed researchers to reconstruct a precise timeline and a fine-grained ecological picture from a narrow slice of rock.

Dinosaur extinction struck without warning

Taken together, the findings restore drama to the dinosaurs’ finale. They weren’t fading out. They were at full strength, diversified across climate-shaped regions, and still evolving when the sky fell. A single, abrupt shock – not a drawn-out decline – closed the Cretaceous chapter.

“The Naashoibito dinosaurs lived at the same time as the famous Hell Creek species in Montana and the Dakotas,” Peppe said. “They were not in decline – these were vibrant, diverse communities.”

“What our new research shows is that dinosaurs are not on their way out going into the mass extinction,” Flynn said. “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.”

The message lands cleanly: timing is everything. With better dates and a wider lens, the last days of the dinosaurs look less like a slow sunset and more like daylight interrupted – bright, busy, and then suddenly gone.

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