Dinosaurs are a diverse group of reptiles that were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period (about 230 million years ago) until the end of the Cretaceous (about 65 million years ago), when the Cretaceous–Paleogene extinction event led to the extinction of most dinosaur species at the close of the Mesozoic era.
There are a number of features which determine whether a reptile is a dinosaur, but one of the most obvious is that unlike most reptiles, the dinosaurs stand erect on their limbs. This makes it easy to differentiate feral dinosaurs from other reptiles such as lizards, but anthro dinosaurs can be harder to tag. Use your best judgment: in some cases it may be better to tag anthros as reptile, instead of something more specific.
Although modern taxonomy considers birds to be avian dinosaurs, for search convenience they should only be tagged as avian and bird. As for dinosaurs with feathers, they should be tagged with feathered dinosaur.