Late-surviving New Mexican dinosaurs illuminate high end-Cretaceous diversity and provinciality

It has long been debated whether non-avian dinosaurs went extinct abruptly or gradually at the end-Cretaceous (66 million years ago), because their fossil record at this time is mostly limited to northern North America. We constrain a dinosaur-rich unit to the south, the Naashoibito Member in New Mexico, to the very latest Cretaceous (~66.4 to 66.0 million years), preserving some of the last-known non-avian dinosaurs. Ecological modeling shows that North American terrestrial vertebrates maintained high diversity and endemism in the latest Cretaceous and early Paleogene, with bioprovinces shaped by temperature and geography. This counters the notion of a low-diversity cross-continental fauna and suggests that dinosaurs were diverse and partitioned into regionally distinct assemblages during the final few hundred thousand years before the end-Cretaceous asteroid impact.