Abstract: From time to time somebody forwards the opinion that between the Mesozoic ,and the Kainozoic some catastrophic event must have happened, to account for the difference in the fauna, especially the extinction of theDinosaurs. This is considered to be wholly unnecessary.1. The faunal change is not as sudden as it seems on superficial observation. Some mesozoic forms disappear already before the conventional boundarybetween the Cretacous ,and the Tertiary, others survive it (v. Ammonoidea ,and Belemnoidea). Modern types (Placentalia, Octopoda) make their appearance alreadyin the Upper Cretaceous. Thus the appearance of new, the extinction of old forms isa drawn-out process, lasting from about Turonia n up to the Eocene, with probablya peak at the top of the Maestrichtian.2. Extinction mainly concerns forms of high specialization which are at theend of an evolutionary cycle. Such forms are susceptible to even small changes inexternal conditions, which do not touch more robust forms. Small initial changesmay lead to a cumulative effect.The faunal change between Mesozoic and Kainozoic is no more catastrophicthan any other in the history of life.