For decades, scientists have debated whether dinosaurs were already in \u00a0decline\u00a0 before their abrupt extinction, or whether they vanished while still thriving. A recent study published<\/a> in the magazine Science<\/em>, featuring Spanish researcher \u00a0Jorge Garc\u00eda-Gir\u00f3n\u00a0 from the \u00a0University of Le\u00f3n\u00a0, offers compelling evidence for the latter scenario. The research refutes the idea of a prolonged decline, suggesting instead that dinosaurs were diverse and segmented into distinct \u00a0ecological regions\u00a0 right before the asteroid impact.<\/p>\n <\/p>\n The Fossils of the South<\/strong>. Much of the uncertainty surrounding this topic arises from a bias in the \u00a0fossil record\u00a0. The only well-dated faunas that span the extinction boundary originate from northern North America, particularly in the renowned \u00a0Hell Creek Formation\u00a0. This localization has made it challenging to determine whether the extinction pattern observed there was \u00a0global\u00a0 or merely local.<\/p>\n The research team turned its attention to a fossil-rich unit farther south, located in the \u00a0San Juan basin of New Mexico\u00a0, known as the Naashoibito Member<\/a>. Controversially, the age of this formation was often considered much older. However, by employing \u00a0geochronology techniques\u00a0 using argon dating and magnetostratigraphy, the study achieved precise dating. The results were clear: the Naashoibito Member dates to the late Cretaceous, approximately 66 million years ago.<\/p>\n This implication is significant; the fossils found in this region comprise some of the final \u00a0non-avian dinosaurs\u00a0 known to have existed. These dinosaurs thrived up to 340,000 years before the impact and coexisted with the fauna from the \u00a0Hell Creek\u00a0 region.<\/p>\n <\/p>\n Separated by Weather<\/strong>. This finding is crucial because it allows researchers to compare two different faunas from the same period at the end of the Cretaceous. Importantly, the results counter the previously held beliefs regarding the decline of dinosaurs.<\/p>\n <\/p>\n The study not only dates the fossils but also employs robust ecological models to analyze the diversity of terrestrial \u00a0vertebrates\u00a0 throughout North America. Findings indicate that far from forming a \u00a0homogeneous\u00a0 and \u00a0cosmopolitan\u00a0 fauna, dinosaurs maintained high diversity and significant \u00a0endemism\u00a0 until their extinction.<\/p>\n <\/p>\n In essence, the research concludes that dinosaurs were “strong” and had distinct \u00a0regional assemblages\u00a0. It identifies two clear bioprovinces in the north and south that remained stable through the late Cretaceous period.<\/p>\n <\/p>\n What differentiated these faunas? The analysis suggests that \u00a0temperature\u00a0 played a critical role. Beyond a simple geographical divide, distinct dinosaur communities adapted to different \u00a0climates\u00a0. For instance, data indicates that warmer southern regions may have been more suitable for \u00a0sauropods\u00a0, while cooler northern areas better accommodated \u00a0hadrosaurines\u00a0.<\/p>\n The compelling sum of the evidence points directly to the fact that non-avian dinosaurs were \u00a0abruptly\u00a0 annihilated at the end of the Cretaceous. Contrary to prior assumptions, they were not in a state of decline that would have already condemned them to extinction. Instead, their ecosystems were diverse and \u00a0biogeographically compartmentalized\u00a0. The extinction event itself was sudden and, subsequently, as the fossil record indicates, it was followed almost immediately by the rapid diversification and rise of mammals.<\/p>\n![\"They](\"https:\/\/teknomers.com\/en\/wp-content\/uploads\/2025\/10\/We-believed-that-dinosaurs-were-close-to-extinction-before-the.jpeg\"\/)
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