Typical ankylosaur skull showing some of the major features (Tarchia gigantea from the Upper Cretaceous of Mongolia).
There are three families of ankylosauria (ankylosaurs); the ankylosaurids, nodosaurids and the polacanthids. Their individual skulls differ much from each other. The polacanthids and the ankylosaurids have a skull that is as wide or wider than long while the nodosaurids have a lengthier, narrower skull. The narrow skull suggests that the nodosaurids were browsers, cropping selective vegetation and plant parts as opposed to a grazer that cropped all low vegetation. However, all three families are missing two of the five skull openings characteristic to most dinosaurs. The antorbital fenestrae on the front orbital and the supratemporal fenestrae on the skull top. The Ankylosaurids are missing an additional pair of openings, the lateral temporal fenestrae positioned behind the orbits.
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