Dinosaurs were not fading away before the asteroid struck

History · Published 24 October 2026 Swipe more like this →

In short: For years, scientists debated whether dinosaurs were already in decline before the asteroid hit 66 million years ago. New fossil evidence from New Mexico suggests a different reality: these giants were flourishing and forming thriving communities right up until the moment of impact.

Recent analysis of fossils from New Mexico provides a vivid picture of life in the southwestern region of North America during the end of the Cretaceous period. These specimens date to within approximately 340,000 years before the six-mile-wide asteroid struck the Yucatán Peninsula. The data suggests that dinosaurs were not fading away; instead, they occupied diverse lowlands and formed robust populations.

The study highlights the presence of true giants like the immense long-necked herbivore Alamosaurus. These creatures dominated the landscape, with some reaching sizes comparable to a jet plane. This evidence challenges previous theories that dinosaur lineages were already in a state of decline prior to the cataclysmic event, which ultimately drove 75 percent of Earth's species to extinction.

This discovery adds nuance to our understanding of mass extinctions and evolutionary radiations. While the asteroid was devastating, it struck a world where dinosaurs were actively thriving. This contrasts with other major biological shifts, such as the radiation of archosauromorphs—the group including dinosaurs and crocodiles—which began about 252 million years ago following the end of the Permian Period.

Understanding these dynamics is crucial for paleontologists mapping evolutionary family trees. By identifying whether a group is in an 'early burst' of speciation or a period of decline, researchers can better understand how biodiversity on our planet is shaped by both gradual evolution and sudden, catastrophic environmental shifts.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• Look up: the most common dinosaur is in your backyard
• The asteroid impact was not the only killer of the dinosaurs
• The era of giants did not end with the dinosaurs
• A thin band of rock holds the secret to the dinosaurs' sudden, violent end.
• Crocodiles survived the dinosaur-killing asteroid partly by eating leftovers
• The catastrophic Tuesday morning that paved the way for human life
• The day the world ended: 75% of life vanished in an instant
• The recurring cycle of life's greatest collapses and rebirths
• The day the world almost ended: Earth's deadliest mass extinction
• How the disappearance of the passenger pigeon changed whiskey production
• The math of extinction: how many species vanish every year?
• Can we breed the ghosts of extinct animals back into existence?

More in Extinction · More in History · Latest · A–Z · All topics