Genasaurians

Genasaurians, also known as genasaurs, are beaked, primarily herbivorous dinosaurs in the clade Genasauria. Paleontologist Paul Sereno first named Genasauria in 1986. The name Genasauria is derived from the Latin word "gena" meaning "cheek" and the Greek word "saúra" (σαύρα) meaning "lizard". Genasauria is the most inclusive clade within the order Ornithischia. According to Sereno (1986), Genasauria represents all ornithischians except for the most primitive ornithischian, Lesothosaurus. Sereno's formal definition is, "Ankylosaurus, Triceratops, their most recent common ancestor and all descendants". It is hypothesized that genasaurians had diverged from Lesothosaurus by the Early Jurassic. Cranial features that characterize genasaurians include a medial offset of the maxillary dentition, a sprout-shaped mandibular symphysis, moderately sized coronoid process, and an edentulous (without teeth) anterior portion of the premaxilla. A distinguishing postcranial feature of genasaurians is a pubic peduncle of the ilium that is less robust than the ischial peduncle. Genasauria is commonly divided into Neornithischia and Thyreophora. Neornithischians are characterized by asymmetrical distributions of enamel covering the crowns of the cheek teeth, an open acetabulum, and a laterally protruding ischial peduncle of the ilium. Neornithischians includes ornithopods, pachycephalosaurs, and ceratopsians. Thyreophorans are characterized by body armor and includes stegosaurs, ankylosaurs, Scelidosaurus, and Scutellosaurus.