Gigantic herbivores and carnivores
The simple peg-like teeth of these animals meant that food, particularly plant material such as the tough leaves of the cycads that existed at that time, had to be broken down in the stomach. Mammals have specialized teeth that break-down and grind food to a considerable extent before entering the stomach for further processing. Consequently herbivorousdinosaurs probably needed large guts and even used stones (gastroliths ) to process their food and this may have been the reason for them becoming so large. Carnivorousdinosaurs, like Tyrannosaurus, would also need to be large to prey on these mega-herbivores. Many Apatosaurusfossil bones have teeth marks which correspond to the fit of carnivorousdinosaur's jaws such as Allosaurus. Some scientists have re-interpreted such findings and have suggested that these apparently carnivores were more likely to have fed on the large carcasses of the mega-herbivores.