Forget the “dinosaurs were already dying” myth. Fresh dating of a fossil-rich layer in New Mexico’s Naashoibito Member (San Juan Basin) places it at roughly 66.4–66.0 million years ago—the final heartbeat before the Chicxulub impact. What the rocks reveal isn’t a languishing world but a living one. These floodplains held mixed herds of hadrosaurs and ceratopsians, stalked by tyrannosaurids, with the towering sauropod Alamosaurus browsing where river channels shifted through sandbars and cottonwo