by Claudine Zap What was the secret to the large size of plant-eating dinosaurs? Scientists say the key was eating fast food, Jurassic-style: gulping down mammoth amounts (but not mammoths ) without chewing . That's the conclusion researchers came to when studying how it was possible for plant-eaters to be just so darn big. The simple rule is, according to a story on Science Daily , the larger the animal, the more time spent eating.