Labels:text | font | paper | publication | black and white | document OCR: For most of the 160 million years that dinosaurs dominated life on land, the Earth's climate was warm and mild. This type of climate encouraged abundant plant growth, and lush vegetation grew to provide food for newly evolving plant-eating dinosaurs. In the Triassic Period (248-208 MYA), the plants that flourished were nonflowering and included cycads (palmlike tropical plants), ferns (plants with leaves divided into many smaller leaves), tree ferns, and horsetails (brushlike plants). These plants also flourished during the wetter Jurassic Period (208-144 MYA), along with forests of conifers (plants that reproduce by making cones). In the Cretaceous Period (144-65 MYA), flowering plants evolved and became the dominant plant types. PLANT-EATING DINOSAURS Different dinosaurs evolved for eating different types of plant food. Their jaws and teeth help us to guess what they ate. The giant, long-necked sauropods ("lizard-footed" dinosaurs) had teeth shaped like pegs or chisels for raking in or cropping tree leaves and ferns. Armoured dinosaurs with narrow beaks and leaf -shaped teeth probably munched low- growing fruitlike growths. Horned dinosaurs and ornithopods ("bird-footed" dinosaurs) with self-sharpening cheek teeth could tackle tougher vegetation. PLANTS AS FOOD Plant-eaters have a great advantage over flesh-eaters: they do not need to hunt for their food. The plant-eater therefore expends less energy in obtaining its food than a flesh-eater. The disadvantage of eating plants is that they have a much lower nutritional value than meat. The plants eaten by dinosaurs were generally tough and fibrous, and needed to be thoroughly crushed and softened up in order to release any nutritional value. In addition, much of the structure of plants is made up of a material called cellulose, which is chemically close to starch but which cannot be digested by animals' digestive juices. Plant-eating dinosaurs adopted various feeding habits in order to derive maximum benefit from their food. Some, perhaps all, plant-eaters had microorganisms living in their digestive systems. These microorganisms were capable of digesting cellulose, so that the dinosaurs could benefit from this otherwise indigestible material. Similar microorganisms can be found in living plant-eaters such as cattle and horses. Most, probably all, plant-eating dinosaurs had long digestive systems to extract the maximum nutritional benefit from their food. SAUROPODS It was once believed that the immense sauropods ("lizard-footed" dinosaurs), such as Apatosaurus, must have survived on soft, water-dwelling plants. It was thought that because their head and mouth were small, and because they did not have many teeth, they would not be able to take in sufficient tough vegetation to keep their large bodies alive. More recently, it has been shown that sauropods used the mouth as a simple inlet for raking in vegetation from trees and shrubs, but maybe mainly ferns. This was swallowed without chewing. The "chewing" of food took place in the gizzard (part of the stomach). This contained gastroliths, stones that had been swallowed by the dinosaur and that ground up vegetation inside the stomach. Some living birds also swallow stones to help crush food in the same way. Most sauropods had a long neck that enabled them to reach vegetation from shrubby trees, and to crop plants at ground level. LARGE ORNITHOPODS Many large ornithopods ("bird-footed" dinosaurs), such as the hadrosaur Corythosaurus, lived and fed in herds, like the modern grazing herds of African savanna. They had large numbers of grating cheek teeth that probably enabled them to feed on tough plants. Corythosaurus herds would have trampled paths through rich forests of magnolias, ferns, palms, and cypress trees, browsing on the vegetation of low-growing trees, and cropping low-growing flowering plants. They would have cropped leaves and fruits with their beak before grinding them into a pulp inside the mouth and swallowing it. The pulped food was probably digested further by enzymes in the stomach and intestines, and possibly by microorganisms. CERATOPSIANS Many ceratopsians ("horned-faced" dinosaurs), including Protoceratops, were herd-living animals that probably wandered within a limited area, feeding on tough vegetation, including ferns and flowering plants. Ceratopsians had a sharp beak to bite off pieces of vegetation, and large numbers of cheek teeth with sharp edges. As the dinosaur's powerful jaws slammed shut, the sharp cutting edges slid past each other and sliced up the vegetation like a pair of scissors. This was probably repeated until the food was finely chopped, when it was swallowed. Once in the stomach, the food may have been further ground up by stomach stones, as it was in the sauropods ("lizard-footed" dinosaurs). Or the food may have been digested by enzymes and microorganisms in order to release food substances that could be absorbed by the body.
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