Overview
- High-precision ages of about 66.4–66.0 million years place the Naashoibito Member within roughly 340,000 years of the Chicxulub asteroid strike, contemporaneous with Hell Creek.
- The assemblage documents diverse dinosaurs including Alamosaurus, Tyrannosaurus, Torosaurus and multiple hadrosaurs, supporting the view that populations were flourishing rather than in long-term decline.
- Comparisons show distinct north–south dinosaur communities across western North America, with sauropods present in New Mexico but absent in Hell Creek, consistent with climate-driven provinciality.
- The team combined argon-isotope radiometric dating of volcanic grains with paleomagnetic polarity data to resolve the long-debated age despite the absence of a boundary clay layer at the site.
- Independent experts praise the robust dating yet caution that conclusions about continent-wide or global trends remain provisional, with the study also noting rapid mammalian diversification within a few hundred thousand years after the extinction.