The armored dinosaurs (Thyreophorans, Thigh-rio-for-ans) were the "tanks" of the dinosaur world. Equipped with armor arranged in longitudinal rows, and often with spikes or a club on the tail, they presented a fortress-like defense to any would-be predator.
The armored dinosaurs include two major groups: the stegosaurs (stegg-oh-soars) and the ankylosaurs (an-kye-low-soars). In both, the forelimbs are much shorter than the hind limbs, thus the hips were raised and the head was held close to the ground. This is most conspicuously evident in the stegosaurs.
The stegosaurs lived from the Middle Jurassic to the Early Cretaceous Period, although they were most common in the Jurassic. They had rows of plates or spikes that ran along the back, protecting the spine. Stegosaur plates were, evidently, well-invested with blood vessels and it has been suggested that they may have helped to control body temperature by acting as heat radiators. It is also possible that they were used as displays to help identify species and sex, or to increase the apparent size of the animal in profile to intimidate predators or competing stegosaurs.
Ankylosaurs lived from the Middle Jurassic to the Late Cretaceous Period. The more advanced members of the group sported an impressive club on the end of the tail. The body was covered in heavy armor, consisting of bony nodules and spikes. Even the eyelids were armored!
Ankylosaurs also had another interesting feature: a "secondary palate" forming the roof of the mouth and separating the air passageway (nasal cavity) from the food passageway (mouth). This is very unusual for a reptile, most of which have nostrils that open directly into the mouth. In advanced ankylosaurs, the air passageway is looped upward and is associated with complex sinuses.
The navigation bar to your left will take you to pages that discuss individual stegosaurs and ankylosaurs.