New Mexico Alamosaurus Fossils Show Dinosaurs Thrived Before Asteroid Impact

Remarkable paleontological discoveries within the Naashoibito Member of the San Juan Basin in northwestern New Mexico are illuminating the final epoch of non-avian dinosaurs. These unearthed remains depict a complex, flourishing ecosystem that existed immediately before the catastrophic mass extinction event 66 million years ago. This finding challenges older narratives suggesting a widespread decline in dinosaur populations prior to the celestial impact.

While northern North America, represented by formations like the Hell Creek Formation, featured species such as the horned Triceratops and the duck-billed Edmontosaurus, the southern New Mexican site yielded evidence of the colossal Alamosaurus. This sauropod is counted among the largest creatures ever to walk the Earth, with estimates suggesting lengths near 100 feet (30 meters) and a mass exceeding 30 tons. The presence of such a massive herbivore thriving in southern territories right up to the moments before the Chicxulub impact suggests robust regional vitality, contradicting any notion of continental malaise.

Dr. Andrew Flynn, an assistant professor at New Mexico State University and the study's lead author, emphasized that the data strongly indicates these magnificent creatures were actively flourishing across North America's southern latitudes just before the extinction. The research team used sophisticated chronological techniques, including magnetic polarity stratigraphy and radiometric dating, to precisely pinpoint the fossils' age. Their analysis constrained the evidence to a narrow 380,000-year window immediately preceding the end-Cretaceous boundary.

This meticulous dating effort, detailed in the study titled "Late-surviving New Mexican dinosaurs illuminate high end-Cretaceous diversity and provinciality," appeared in the October 23, 2025, issue of the journal Science. The research underscores that the dinosaurian realm was not monolithic, revealing distinct regional faunas, each with its own trajectory before the global reset. The investigation into these southern ecosystems reveals a richer, more resilient tapestry of life than previously assumed for that terminal timeframe, shifting the narrative from slow decay to sudden, dramatic cessation caused by overwhelming external forces.