Thanks to the fossils that have been discovered in the past two hundred years and the studies by paleontologist, we have a fair idea of the diet of dinosaurs. There were two main orders of dinosaurs . One is called the Saurischia, being lizard hipped and the other is Ornithischia being bird-like hipped and each had their own diet.To understand fully what dinosaurs ate we have to look at the different stages that took place in the food chain. The food chain went in the order of tertiary consumers that ate secondary consumers, secondary consumers that ate primary consumers, primary consumers ate producers and the producers were the plants. Some dinosaurs were carnivores but others were herbivores. Food chains must have more organisms at the lower end of the chain food due to the transfer of food energy being efficient and much of the energy is absent at each stage of the process.
The process goes like this. A large number of plants (producers) can support a smaller number of plant eater's (primary consumers) these animals in turn are eaten by the Carnivores (secondary consumers). A good example is, it would have taken hundreds of acres of plants to feed a small group of Triceratops; these in turn may possibly feed a single T-Rex with enough food to see it during its lifetime.
In the dinosaur genera, plant eaters rated approximately 65% and meat eaters took up 35%. Considering the number of dinosaur fossils found, the plant eaters increased. This is scientifically proven by the overwhelming quantity discovered. In relationship to this only there have not been as many T. Rex fossils discovered. When the number of carnivores increases in a community the herbivores decrease, it's the natural way of things. Eventually it would have become harder and harder for a carnivore to find food which in turn would decrease the carnivores population. This controls the stability of each group and this stability also existed between plants and plant eaters.
Plant eaters were Herbivores. These dinosaurs usually had to consume a lot more food than carnivores in order to get the quantity of nutrition they required. Some of their diet consisted of leaves, twigs and roots that didn't hold much worth in nutrition. Their digestive systems would be bigger than carnivores to process the immense intake of food. Some of these dinosaurs would consume rocks to help grind up their food in their stomach. Some had fermentation chambers where plants would set until they dissolved.
There are not many fossils with the stomach contents that have been found which leaves the scientist guessing as to what a dinosaur's diet consisted of but they can speculate from the evidence they have obtained by other means such as the teeth. the teeth can give scientist a good idea of what form of climate it lived in and what kind of plants was obtainable at the time but these are all constraints in finding out accurately what an herbivores diet was. For example during the Mesozoic period the most probable plants would have been ferns, cycads, horsetails, club mosses, seed ferns, conifers and gingko's. The Cretaceous period brought flowering plants.
Meat eaters such as carnivores or theropods had very physically, powerful legs, to sprint and seize prey but they also required strong jaws, claws and sharp teeth to hunt down and shred their prey apart. They also needed superior eye sight, an intense sense of smell and a brain huge enough to plan a hunt and kill. It is feasible that they hunted in packs so they would require social cooperation this can be substanciated by the closness of some of the fossils found. Carnivores were most probable to be scavengers as well. The teeth had to be razor-sharp indeed to shatter bones and get at the nutritional marrow inside. Some dinosaurs ate fish, such as the Baryonyx and the Suchomimus and a number of dinosaurs like the Coelophysis were discovered with tiny fossilized animals inside of them. It is thought that some dinosaurs could have even been cannibals, eating their own kind.
There were only a few of dinosaurs that were Omnivores which meant they ate plants as well as animals. The ornithomimus and Oviraptor ate a variety of plants, eggs and insects. Eating insects could have happened by accident, when they were eating plants there would have surely been insects ingested and maybe sometimes small animals.
There were a few oddballs in dinosaurs such as the Gallimimus which was a late ornithomimid dinosaur. This dinosaur ate by sieving tiny bits of food such as tiny crustaceans from mud and waters that they fed in. They did this by using their comb like plates inside their mouth to strain the food that they sucked in.
There have been many studies done on diets of dinosaurs and some of the studies consist of fossilized feces which are called Coprolites and other helpful finds. Coprolites help identify a dinosaurs feeding behavior. Recently a large coprolite was found in Canada that is thought to have come from a T. Rex. It contained crushed bone which told the scientist the dinosaur had not eaten the bone whole. A real remarkable and rare find was a Baryonyx whose stomach contained fish scales. A Sinosauropteryx which is a bird like dinosaur was found with parts of a small unidentified mammal in its stomach.
Teeth structure also help to a great extent to give scientist clues as to what they ate. They found that a meat eaters teeth were sharp for tearing flesh and strong teeth for crushing animals. Plant eaters had special teeth, these were teeth that could strip and chew plants. Gizzard stones also lets scientist look into the past with clues about a dinosaurs diet. These have been found in some fossils and leave clues to what their diet would have been. The size of the gut is another clue to a dinosaur's diet. Plant eaters had very bulky guts due to the quantity of food they ate to maintain their nutrition and great size. Scientists know that this would necessitate a great digestive system.
Although we have a fair idea of what dinosaurs ate we don't know exactly but with all these fossil clues put together it certainly gives scientist a fair idea of what type of diet they enjoyed. We are learning more all the time and with the fossils that are still being found around the world, one day we won't have to wonder any longer. We will know for sure without a doubt.