Triceratops horridus by Todd Marshall (2004)

  • Large bony ridge, or thickened region at the back of the skull
  • The primitive forms of Marginocephalia were bipedal, such as Pachycephalosaurus, but the later forms had such huge heads, and heavy elephantine bodies that they became obligate quadrupeds
  • Many forms had cranial ornamentation for either display or combat
  • They originated during the Early Cretaceous

Cladogram courtesy of T.Holtz Jr. 2004 (


These animals are often shown head butting, where males would run at each other and crash their heads together. This behaviour is debated, as their massive thickened skull roofs are not as strong as might be expected. Their thickened skulls could have been used in defence or display. Pachycephalosaurs were all bipedal animals, with very wide ribcages indicating that they had the long intestinal track of a herbivore.


  • These animals had skeletons very similar to the hypsilophodonts, but the skull was specialized
  • The top of the skull was thickened into a dome that was up to 22.5 cm thick
  • Examples: Stegoceras, Stygimoloch, Pachycephalosaurus

Pachycephalosaurus wyomingensis by Emma Schachner (2004)


The ceratopsians, represented by Triceratops, are one of the best known groups of dinosaurs. They had the largest skulls of any of the dinosaurs. Most ceratopsians were quadrupedal, and they were all herbivorous. Tyrannosaurus rex preyed on ceratopsians.



  • Large frill at the back of the skull covering the neck
  • Skulls so large that they made up 20% or more of the entire body length
  • Most were quadrupeds, with a body stature like modern rhinos
  • Many developed large horns and spikes on their faces, the most common being a horn on the nose, and over the eyes or extending from the frill


All of these animals have been discovered in Western North America, and have been found to have lived in herds. They also show nasal and orbital (eye) horns of different sizes and shapes

  • (1) Centrosaurine - short, robust heads, with small horns over the eyes, with long nasal horns.
  • (2) Ceratopsinae (Chasmosaurinae) - large heads with very long horns over the eyes, and longer faces. (Example : Triceratops)

Triceratops skull by P. Olsen (2004) based on Hatcher et al. (1907)

Author: Emma Schachner
Last updated: 13 November 2004
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