The “poison plant” theory of dinosaur extinction involves the development of angiosperms (flowering plants), a new type of plant that first flourished during the Cretaceous period. Some of the plants were no doubt poisonous to dinosaurs, and the plants probably developed protective toxins to prevent being eaten. The more prolific plant-eating dinosaurs may have died out as the plants became more toxic to these animals; in turn, the carnivores had fewer plant-eating dinosaurs to eat.

But this theory is too simplistic. There were many plants in the world, including varieties that were non-poisonous. In addition, the idea does not explain the mass extinction of marine organisms—animals that had nothing to do with flowering plants on land—at the end of the Cretaceous period.