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).
Figure 6.1. Cladogram of Ornithischia, emphasizing Cerapoda and Margino cephalia. Derived characters include: at 1, significant diastem between premax-illary and maxillary teeth, five or fewer maxillary teeth, finger-like anterior trochanter; at 2, narrow parietal shelf obscuring occipital elements in dorsal view, lateral portions of shelf formed by squamosal.
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.
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