What is Genasauria?

The least inclusive clade containing Ankylosaurus magniventris, Triceratops horridus and Parasaurolophus walkeri. Genasauria is the major clade that includes all ornithischian dinosaurs except the most basal forms such as heterodontosaurids. In practical terms, it is the split within Ornithischia that yields two of the great herbivorous lineages: Thyreophora (the armoured dinosaurs) and Neornithischia (the ornithopods, pachycephalosaurs, and ceratopsians). It marks the point—by the Early Jurassic—where the earliest, lightly built ornithischians give way to the plant-eating lineages that developed far more sophisticated ways of processing vegetation.

Members of Genasauria evolved a toothless beak at the tip of the snout for cropping plants, and their upper teeth sat slightly inset from the outer edge of the jaws—an arrangement that likely supported fleshy cheeks to keep food in the mouth while chewing. The front of the lower jaw formed a short, rounded "spout", and the jaw joint and muscle attachments were shaped to allow stronger, more controlled biting. Across their roughly 120-million-year history, those adaptations helped genasaurians become the most diverse, widespread, and successful medium-to-largeish plant-eaters of the Jurassic and Cretaceous—even as giant sauropods continued to dominate the very largest herbivore roles.

Basically, Genasauria is Ornithischia without the basal ornithischians, most of which are known as heterodontosaurids.

Click here to search DinoChecker for Genasaurians. Genasauria is derived from the Latin "gena" (cheek), and the Greek "sauros" (lizard) and "-ia" (a plural-forming suffix), named for all ornithischians with muscular cheeks.