What Are the Two Classes of Dinosaurs?

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Beginning in 1887, dinosaurs have been divided into two main categories: saurischian, which means "lizard hipped," and ornithischian, which means "bird hipped." This classification is based on the dinosaurs' pelvic bone structure. Though the name "bird hipped" may seem to indicate that these prehistoric animals are related to birds, that is not necessarily the case.

Instead, the two categorizations are based on differences in pelvic anatomy, with the lizard-hipped dinosaurs possessing a narrower pelvis than the bird-hipped dinosaurs. There are bipedal and quadrupedal dinosaurs in both categories, and each category also contains herbivorous dinosaurs. The saurischian class is the only one known to contain carnivores.