The evidence for dinosaur evolution was reviewed, along with the various theories of dinosaur evolution and the evidence for their support. Dinosaurs are commonly believed to have evolved from a small, crocodile-like animal; however, a review of the known fossils provides no evidence for dinosaur evolution from non-dinosaurs, despite the excellent and abundant dinosaur fossil record. This finding is very significant because the bones of many of the average- to larger-sized dinosaurs discovered to date are usually fairly well preserved due to their large size and thickness. Dinosaurs appear abruptly in the fossil record and disappear just as suddenly. The fossil findings for several major dinosaur species also were reviewed.