Abrictosaurus
Abrictosaurus is usually thought to be the most basal member of the family Heterodontosauridae. Lycorhinus and Heterodontosaurus both had high-crowned cheek teeth, which went over each other in the jaw, making a continuous chewing surface analogous to those of Cretaceous hadrosaurids. Abrictosaurus had more widely-split cheek teeth, with lower crowns, more similar to other early ornithischians.