Marginocephalians 1: were a group of bipedal and quadrupedal ornithischian dinosaurs with a narrow
shelf or deep, bony frill at the back of the skull. Marginocephalians were probably descended from the same ancestor as the ornithopods and lived in what are now North America, Africa, Asia, and Europe during the Cretaceous period (145–65 million years ago). They were divided into two groups: Pachycephalosauria (“thick -headed lizards”), such as Pachycephalosaurus and Stegoceras, and Ceratopsia (“horned faces”), such as Triceratops and Psittacosaurus. The thick skulls of Pachycephalosauria may have protected their brains during possible head-butting contests fought to win territory and mates; their hips and spines may also have been strengthened to withstand the shock. The bony frill of Ceratopsia would have added to their frightening appearance when charging; the neck was strengthened for impact and to support the huge head, with its snipping beak and powerful slicing toothed jaws. A charging ceratopsian would have been a formidable opponent for even the largest predators. Ceratopsians were among the most abundant herbivorous dinosaurs of the
Late Cretaceous period (97–65 million years ago).
