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Both paleontologic tradition and current opinion among paleontologists favor the existence of a gradually accelerating biologic crisis at the close of Cretaceous time. The dinosaurs are conventionally postulated to have slowly declined to extinction as a result of stresses generated by terrestrially limited causes. The siderophile anomaly associated with the extinction interval was not predicted by gradualistic models, and is considered irrelevant to the extinction process by some paleontologists although others are puzzled by it and by the peculiar pattern of the extinctions. Evidence that the dinosaurian extinctions were preceded by a gradual decline or were diachronous in different regions of the globe has not been convincingly demonstrated.