In a new explanation for mammals' evolutionary victory over dinosaurs, researchers said a mathematical model has shown that infant size was the clincher.
Given physical limitations to egg size, dinosaurs had comparatively small young. Some came out of the egg weighing as little as two to 10 kilograms, yet had to bulk up to a hefty 30 or 50 tonnes.
Growing up, the youngsters had to compete in several size categories with adults of other animal groups for food, University of Zurich scientist Marcus Clauss told AFP.
This meant that all the small and medium animal size categories supported by the natural environment were "occupied", leaving no room for smaller dinosaur species in which to thrive, according to the findings published in Biology Letters, a journal of Britain's Royal Society.