Heterodontosaurids belong to the family Heterodontosauridae. The name means 'different toothed lizards', and refers to the unusual pattern of teeth possessed by these dinosaurs: they had three kinds of teeth: cutting incisors in the front upper jaw, ridged cheek teeth, and canine teeth fitting into sockets.

These dinosaurs lived from the Late Triassic through to the Early Jurassic period and were primitive ornithopods. Only 4ft long, their remains have been found in Argentina, southern Africa, and possibly also China. Example genera are Geranosaurus, Heterodontosaurus and Lycorhinus.

Heterodontosaurus is the species which gives its name to this family. An Early Jurassic dinosaur discovered in southern Africa, Heterodontosaurus was the first ornithischian known from extensive fossil evidence. It was a 4ft long herbivore and could probably run quite fast. Like the other heterodontosaurids it had small, sharp cutting teeth, short, curved incisors and a number of cheek teeth that chewed plant matter.