To what group did all the meat-eating dinosaurs belong?

All of the carnivorous, or meat-eating, dinosaurs belonged to the theropods, or bipedal carnivores. These dinosaurs, along with the large, herbivorous sauropods, made up the saurischian dinosaurs. This group represents a wide range of dinosaur species from the large Tyrannosaurus to the small Compsognathus.

Duck-billed dinosaurs such as this Corythosaur had special teeth within their unusual mouths for grinding up plants (Big Stock Photo).

What adaptations enabled carnivorous dinosaurs to eat meat?

All of these dinosaurs, known as the theropods, shared many adaptations specific to the catching, killing, eating, and digesting of meat. These animals had larger, sharper, and more pointed teeth than their herbivorous cousins; they were used to kill the victim and tear the flesh off the body. To power these teeth and to break down the nutritious bone marrow from their prey they needed strong jaws and muscles.

The carnivores also had clawed feet for slashing their victims, with the dromaeosaurids possessing the epitome of this adaptation: large, sickle-shaped foot claws.

The theropods, being bipedal, had their arms and hands free to grasp their prey; their fingers often had claws used to slash and hold the victim. Being bipedal, they had the relative speed and agility to catch their prey, especially sick and ailing animals. It is thought by some scientists that the theropods had good eyesight, a keen sense of smell, and a large brain (in proportion to its body) to calculate hunting strategies.

What adaptations did the herbivorous dinosaurs have that enabled them to eat plants?

Some herbivorous dinosaurs did not chew at all, but merely swallowed whole the vegetation they pulled off a tree or bush. They had larger (and probably more rugged) digestive tracts than carnivorous dinosaurs in order to digest the tough, fibrous plants they ate. Some herbivores, such as the Ankylosaurus, even had fermentation chambers along their digestive tract in which tough fibers would be broken down by bacteria. In addition, some herbivores had gastroliths, or gizzard stones, in their digestive tract, which would grind up the fibrous plants, helping to digest the material. (It is interesting to note that this method is similar to how birds swallow stones to grind up ingested matter in their digestive tracts.) These stones were deliberately swallowed, and are often found with fossils of herbivores. Both of these actions prepared the vegetation for digestion.

Other herbivorous dinosaurs, like the duck-billed hadrosaurs, had special teeth that would grind up the food before swallowing. Ceratopsians like the Triceratops had sharp teeth and powerful jaws that enabled them cut through tough plants. Still other herbivores had cheek pouches, apparently used to store food for later ingestion. They probably concentrated their meals on certain plants, especially the ancestors of the conifers, flowering plants, horsetails, ferns, and cycads that grow today.

What was an omnivorous dinosaur?

An omnivorous dinosaur was one that ate both plants and meat. There are only a few known omnivores among the dinosaurs, including Ornithomimus and perhaps Oviraptor, although new fossil finds may change scientists opinion about the latter. A diet of an omnivorous dinosaur could include different types of plants, insects, eggs, and small animals. These omnivorous dinosaurs were probably rare, only eating this way out of necessity, such as when there was a sudden lack of meat or plants in their surrounding habitat. Others believe these dinosaurs were omnivores by accident, eating insects and small animals as they ate the plants around them.

Have any fossilized stomach contents of dinosaurs been found?

Although rare, some dinosaur stomach remains have been found over the years. The best examples are from carnivorous dinosaurs: The fossilized remains of a lizard (Bavaisaurus) were found in the gut region of a carnivorous dinosaur called Compsognathus no doubt the dinosaurs last meal. In addition, Coelophysis fossils have been found with the fossilized remains of other Coelophysis dinosaurs inside the gut region, indicating these dinosaurs probably engaged in cannibalism. Whether this was active predation or scavenging has not been determined.

The stomach contents of herbivorous dinosaurs have not been as definitive, however, due to the organic nature of the material. One case was reported in the early 1900s, where the fossilized remains of an Edmontosaurus had been found with conifer seeds, twigs, and needles in the body cavity. However, it could not be determined if these were actual stomach contents, or just debris that had subsequently washed into the carcass.

Did other animals prey on dinosaurs?

Yes, and in 2005, a 130-million-year-old mammal fossil found in China was important evidence of this. A fossil of a cat-sized mammal known as Repenomamus robustus was found with a small dinosaur preserved in its stomach area. This was the first direct evidence that mammals preyed on dinosaurs.

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