 The extinction of the ammonites, along with other marine animals and non-avian dinosaurs, has been attributed to the K-Pg extinction event, marking the end of the Cretaceous Period.Eight or so species from only two families made it almost to the end of the Cretaceous, the order having gone through a more or less steady decline since the middle of the period.Six other families made it well into the upper Maastrichtian (uppermost stage of the Cretaceous), but were extinct well before the end.