What Are Dinosaurs?

Dinosaurs first appeared about 230 million years ago. Dinosaurs were extremely varied animals. The same goes for the animals that lived alongside them.

Saurischians
One of the two main groups of dinosaurs were the saurischians. This group included sauropods, prosauropods, and theropods. This group contained some of the largest predators ever and some of the largest animals in general.

Ornithischians
The other group of dinosaurs were the ornithischians. This group included dinosaurs like hadrosaurs, iguanodonts, hypsylophodonts, stegosaurs, ankylosaurs, ceratopsians, and pachycephalosaurs. This group included only herbivores.

Non-Dinosaurs
A number of animals lived alongside the dinosaurs. Other reptiles like mosasaurs, pliosaurs, ichthyosaurs, plesiosaurs, pterosaurs, crocodilians, and others were present. A number of mammals also lived alongside them. Dinosaurs had to cope with and compete with these animals, as well as each other.