Marginocephalians are a group of Ornithischian (bird-hipped) dinosaurs that have a distinctive skull structure (a slight shelf or bony frill on the back of the skull), a unique palate (part of the mouth) and a short pubis (part of the hip). These plant-eaters include the Ceratopsians (horned dinosaurs like Triceratops, Styracosaurus, Pentaceratops, Protoceratops, etc.) and the Pachycephalosaurians (thick-skulled dinosaurs like (Stegoceras, Pachycephalosaurus, etc.). Marginocephalians may have evolved from the closely-related Ornithopods.

Protoceratops:

Protoceratops walked on four legs, had a large head, a bulky body, a parrot-like beak, cheek teeth, and a small frill on its head. Males may have had larger frills than females, indicating that the frill may have been used in courtship and mating.

Protoceratops was about 6 to 8.2 feet (1.5-2.5 m) and weighed roughly 900 pounds (400 kg). It was about 3 feet tall (to the top of the shoulders). Protoceratops lived in the late Cretaceous period, about 86 to 71 million years ago, toward the end of the Mesozoic, the Age of Reptiles. Protoceratops was possibly a herding animal, like several other ceratopsians. This hypothesis is supported by the decision of bone beds, large deposits of bones of the same species in an area, and large groups of nests. Each nest had 12 or more eggs, laid in a spiral fashion.Protoceratops was an herbivore, a plant eater. It probably ate cycads and other prehistoric plants with its tough, hook-like beak.Protoceratops walked on four short legs; it was a relatively slow dinosaur. Dinosaur speeds are estimated using their morphology (characteristics like leg length and estimated body mass) and fossilized track ways.

Styracosaurus:

Styracosaurus was a dinosaur that walked on four short legs. This large plant-eater had a six-spiked frill projecting from the back of its skull. It also had an upward-pointing horn on its nose (2 feet (60 cm) long and 6 inches (15 cm) wide), and two small horns above its eyes. These spikes and the horn probably provided protection from predators, and were possibly used in mating rituals and rivalry. It had a short, thick, pointed tail, a large, bulky body, a large skull and a beak. Styracosaurus hatched from eggs. Styracosaurus was about 18 feet (5 m) long, 6 feet (1.8 m) tall, and weighed up to 3 tons.

Styracosaurus lived in the late Cretaceous period, about 77-70 million years ago. It was among the last of the dinosaur species to evolve before the Cretaceous-Tertiary extinction 65 million years ago. Among the contemporaries of Styracosaurus were Tyrannosaurus rex, Ankylosaurus (an armored herbivore), Corythosaurus (a crested dinosaur), and Dryptosaurus (a meat-eating dinosaur). Styracosaurus may have been a herding animal, like some other ceratopsians. This hypothesis is supported by the finding of bone beds, large deposits of bones of the same species in an area. Styracosaurus hatched from eggs, and the young may have been cared for by parents.When threatened by predators, Styracosaurus may have charged into its enemy like a modern-day rhinoceros does. This would have been a very effective defense.Styracosaurus probably ate cycads, palms, and other prehistoric plants with its tough beak. It could also chew well with its cheek teeth (like other ceratopsians, but unlike most other dinosaurs).

Notoceratops:

Notoceratops was a ceratopsian (a frilled, horned, quadrupedal, herbivorous dinosaur with a beak) known only from a late Cretaceous jaw bone. Notoceratops walked on four sturdy legs, had a large head, a bulky body, a parrot-like beak, cheek teeth, and a small frill on its head.Notoceratops lived in the late-Cretaceous period, about 83-73 million years ago, toward the end of the Mesozoic, the Age of Reptiles. Notoceratops may have been a herding animal, and probably laid eggs, like other Ceratopsians. Notoceratops was an herbivore, a plant eater. It probably ate cycads and other prehistoric plants with its tough, hook-like beak.

Triceratops:

Triceratops was a rhinoceros-like dinosaur. It walked on four sturdy legs and had three horns on its face along with a large bony plate projecting from the back of its skull (a frill). One short horn above its parrot-like beak and two longer horns (over 3 feet or 1 m long) above its eyes probably provided protection from predators. The horns were possibly used in mating rivalry and rituals. It had a large skull, up to 10 feet (3 m) long, one of the largest skulls of any land animal ever discovered. Its head was nearly one-third as long as its body. Triceratops hatched from eggs.Triceratops was about 30 feet long (9 m), 10 feet tall (3 m), and weighed up to 6-12 tons.Triceratops lived in the late Cretaceous period, about 72 to 65 million years ago, toward the end of the Mesozoic, the Age of Reptiles. It was among the last of the dinosaur species to evolve before the Cretaceous-Tertiary extinction 65 million years ago.

Montanoceratops:

Montanoceratops walked on four legs, had a large head, a bulky body, a parrot-like beak, a small nose horn, cheek teeth, and a small frill on its head. Males may have had larger frills than females, indicating that the frill may have been used in courtship and mating.Montanoceratops was up to 6 feet long (1.8 m) and weighed about 900 pounds (400 kg). Montanoceratops lived in the late-Cretaceous period, about 72 to 65 million years ago, toward the end of the Mesozoic, the Age of Reptiles.Montanoceratops was an herbivore, a plant eater. It probably ate cycads and other prehistoric plants with its tough, hook-like beak.