Chapter objectives

• Introduce Marginocephalia, particularly its two large constituent groups, Pachycephalosauria and Ceratopsia

• Develop familiarity with current thinking about lifestyles and behaviors of marginocephalians

• Develop an understanding of marginocephalian evolution using cladograms, and an understanding of the place of Marginocephalia within Dinosauria

Marginocephalia

Who were marginocephalians?

Marginocephalia (margin – edge; kephale – head). It's not a name you'll hear from the local 5-year-old dino-it-all. Yet, the name Marginocephalia reflects an important connection between two major, superficially different-looking, groups of dinosaurs: Pachycephalosauria (pachy – thick;) and Ceratopsia (kera – horn; ops – face). Together with Ornithopoda (Chapter 7), marginocephalians make up the taxon known as Cerapoda (Figure 6.1).

Marginocephalians all bear a ridge, or shelf, of bone running across the back of the skull. The size of this feature varies greatly, but in all cases, when viewed from above, it blocks from sight the bones at the back of the skull.

Although marginocephalians come in many shapes and sizes, they were restricted to the Northern Hemisphere during the Cretaceous Period.

Marginocephalia: Pachycephalosauria – In Domes We Trust

Pachycephalosaurs were bipedal ornithischians with thickened skull roofs (Figure 6.2). In the North American pachycephalosaurs, this took the form of high domes, but several Asian varieties had flattened, thickened skulls (Figure 6.3); some, however, are considered to be juvenile forms of fully adult dome-headed pachycephalosaurs. Figure 6.4 shows the distinctive Northern Hemisphere distribution of pachycephalosaur sites.