Final answer:
The clade defined by having asymmetrical tooth enamel in ornithischians is the Ornithopods. This group is different from the Saurischians, which encompasses the lineage that led to modern birds.
Step-by-step explanation:
The clade that is defined by the feature of ornithischians having asymmetrical tooth enamel is Ornithopods. Ornithischians, or "bird-hipped" dinosaurs, include a variety of subgroups, one of which is the ornithopods. This clade is distinct from the Saurischians, which includes the Sauropodomorphs and the Theropods. Despite the similarity in the name, "bird-hipped" (Ornithischia), it was the "lizard-hipped" dinosaurs (Saurischia), specifically the theropods, that gave rise to birds. Theropods shared many characteristics with birds and are part of the evolutionary lineage that includes modern birds.