Dinosaurs were terrestrial animals that are most closely comparable to reptiles of the extant animals. However, they had certain characteristics that distinguish them from any living reptile. And, there are many unknowns about their physiology and anatomy that might make them more like or less like our familiar reptiles.
With all the many genera and species of dinosaurs, it is easy to be confused. However, there are some underlying order that helps keep all the beasts understandable. The dinosaur remain are found in all major layers of the Mesozoic.
Other reptile remains are also found in the layers of the Mesozoic that are not dinosaurs. These include the flying reptiles and the aquatic reptiles that are now extinct as well as reptiles, such as crocodiles and turtles, that are living today.
The Sauropods were the largest terrestrial animals known. Typically they were massive beasts with long a neck and tail, small head with peg-like teeth moving about on all four feet.
The pubic bone in the Ornithichians points to the rear leaving an unobstructed "gut" region. Perhaps this suggests a relatively inefficient fermentation type of digestion based upon a large volume of material slowly being digested.