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Were more dinosaurs plant-eaters or meat-eaters?
There were many more plant-eaters!
Some dinosaurs were carnivores (meat-eaters) but most were herbivores (plant-eaters). In any food chain, there have to be more organisms at the lower levels of the chain because the transfer of food energy is inefficient and much of the energy is wasted. During the Mesozoic Era (as in other times), plant diversity was greater than animal diversity.
A large number of plants (producers) can support a smaller number of plant-eaters (primary consumers). These plant-eaters are eaten by a smaller number of carnivores (secondary consumers).
For example, it may have taken hundreds of acres of plants to feed a small group of Triceratops. These Triceratops could supply a single T. rex with enough food to survive over its lifetime.
If you look at dinosaur genera, roughly 65 percent of the dinosaurs were plant eaters and 35 percent were meat-eaters (or omnivores). If you look at the number of actual fossils found, the percentage of plant-eaters increases, since many fossils of some of the plant-eaters have been found. For example, over a hundred Protoceratops fossils have been found, but only about a dozen T. rex fossils have been found.
As the number of carnivores in a community increases, they eat more and more of the herbivores, decreasing the herbivore population. It then becomes harder and harder for the carnivores to find herbivores to eat, and the population of carnivores decreases. In this way, the carnivores and herbivores stay in a relatively stable equilibrium, each limiting the others population. A similar equilibrium exists between plants and plant-eaters.
Plant-eaters (herbivores) usually have blunt teeth that are good for stripping vegetation (leaves, twigs, etc.). Some also have flat teeth for grinding tough plant fibers. Many herbivores have cheek pouches in which they can store food for a while. Plant-eaters also usually have larger digestive systems that are needed to digest the tough fibers. Sometimes these dinosaurs swallowed rocks (called gastroliths) to help grind up the fibers in their guts. Some (like Ankylosaurus) even had fermentation chambers, where the plant fibers were dissolved.
The only way to know exactly which plants a particular dinosaur ate is to find its fossilized stomach remains or coprolites (fossilized dung) containing digested plant material. Fossilized stomach remains are extremely rare, and coprolites are hard to match up to a particular dinosaur. Given these limitations, all you can do is guess a dinosaur's diet based on the type of teeth the dinosaur had (could it eat soft or tough plant material), where it lived (climate, habitat, etc., which aren't generally known), and which plants were around during that particular time period (for plants that lived during the Mesozoic, click here). For most dinosaurs, you just have to guess (given the constraints listed above) among likely plants, including ferns, cycads, horsetails, club mosses, seed ferns, conifers, and gingkos, abounded during the Mesozoic Era. Flowering plants evolved during the Cretaceous period.
Herbivorous dinosaurs include: Ankylosaurus, Apatosaurus, Camarasaurus, Diplodocus, Dryosaurus, Euoplocephalus, Heterodontosaurus, Hypsilophodon, Iguanodon, Kentrosaurus, Lambeosaurus, Lesothosaurus, Maiasaura, Massospondylus, Montanoceratops, Pachycephalosaurus, Parasaurolophus, Protoceratops, Riojasaurus, Sauropelta, Seismosaurus, Stegoceras, Stegosaurus, Styracosaurus, Supersaurus, Triceratops, Ultrasauros, Xiaosaurus, Zigongosaurus, and many, many others.
Meat-eaters (carnivores or theropods) need to have some way to get meat. Carnivorous dinosaurs usually had long, strong legs so that they could run fast in order to catch their prey. They also needed big, strong jaws, sharp teeth and deadly claws that could kill and then tear apart the prey. Good eyesight, a keen sense of smell, and a large brain to plan hunting strategies are also very important for successful hunting. Many of the carnivores (like Deinonychus, Coelophysis and Velociraptor) may have hunted in packs, so social cooperation was necessary for a good hunt. Animals that are primarily scavengers (animals that eat meat that they did not kill themselves) need very sharp teeth and strong jaws for tearing into the meat and breaking the bones for nutritious bone marrow. Most carnivores are scavengers when given the opportunity. Some dinosaurs were fish eaters, including Baryonyx and Suchomimus. Some carnivores (like Coelophysis) were cannibals, eating their own kind.
Carnivorous dinosaurs include: Albertosaurus, Allosaurus, Coelophysis, Compsognathus, Deinonychus, Dilophosaurus, Eoraptor, Giganotosaurus, Megalosaurus, Suchomimus, Tyrannosaurus rex, Unenlagia, Utahraptor. Velociraptor, Yangchuanosaurus, and many others.
Only a few of the known dinosaurs were omnivores (eating both plants and animals). Some examples of omnivores are Ornithomimus and Oviraptor, which ate plants, eggs, insects, etc. Also, most herbivores are "accidental omnivores" in that when they are eating plants, they also ingest a lot of insects and small animals.
STUDYING DINOSAURS' DIETS
There are many different ways to study dinosaurs' diets, including looking at:
For more information on the predator/prey relationships between dinosaurs, click here.
- Fossilized feces - Coprolites help identify dinosaurs' feeding habits. Recently, in Canada, a large coprolite was found that probably came from a T. rex. The coprolite contained crushed bones, indicating that T. rex crushed the bones of its prey and did not simply swallow things whole.
- Fossilized stomach contents - these are very rare to find. Some unusual finds include Baryonyx, whose stomach contained fish scales, and Sinosauropteryx, a bird-like dinosaur which is the only dinosaur whose stomach contained parts of a small, unidentified mammal.
- Teeth - A dinosaur's tooth structure also tells us what type of food the dinosaur ate. Meat eaters need sharp teeth for tearing flesh or strong teeth for crushing animals; plant eaters have teeth that could strip, and sometimes chew, foliage.
- Gastroliths - Gizzard stones (which aided digestion), have been found with some dinosaur fossils. These also yield information about dinosaur diets.
- Girth - Gut size is also an indicator of diet. Large plant eaters need a lot of calories to sustain their mass. In order to get sufficient energy from plant matter, a lot of vegetation must be digested. This requires a large digestion area.
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