Physiology of dinosaurs way as sauropods. The pachycephalosaurs had small heads and weak jaws and teeth, but their lack of large digestive systems suggests a different diet, possibly fruits, seeds, or young shoots, which would have been more nutritious to them than leaves. On the other hand, ornithopods such as "Hypsilophodon", "Iguanodon" and various hadrosaurs had horny beaks for snipping off vegetation and jaws and teeth that were well-adapted for chewing. The horned ceratopsians had similar mechanisms. It has often been suggested that at least some dinosaurs used swallowed stones, known as gastroliths, to aid digestion by grinding their food in muscular gizzards,
Physiology of dinosaurs endotherms, the larger forms could have been inertial homeotherms, or that many dinosaurs could have had intermediate metabolic rates. The earliest dinosaurs were almost certainly predators, and shared several predatory features with their nearest non-dinosaur relatives like "Lagosuchus", including: relatively large, curved, blade-like teeth in large, wide-opening jaws that closed like scissors; relatively small abdomens, as carnivores do not require large digestive systems. Later dinosaurs regarded as predators sometimes grew much larger, but retained the same set of features. Instead of chewing their food, these predators swallowed it whole. The feeding habits of ornithomimosaurs and oviraptorosaurs are a mystery: although