Fig. 2. A in Function and evolution of ankylosaur dermal armor

Fig. 2. A spike from the polacanthid Gastonia (DMNH 49754−4) from the Lower Cretaceous Cedar Mountain Formation of Utah. A. External surface photograph of specimen. B–D. Thin−section of a spike, dashed lines in A indicate cutting planes. The cortex in the sections is relatively thin. Note that cavities between trabeculae in the cancellous bone are proportionally larger than those of ankylosaurid and nodosaurid cancellous bone: dark gray, cortical bone showing woven or structural fiber bone; white, cancellous bone built up of bone trabeculae that show primary bone tissue in most parts; photograps (B1–D1), interpretive drawings (B2–D2). E, F. Cortical bone tissue of the spike. Detail of the cortex and inner trabecular bone of Gastonia spike in normal (E) and polarized (F) light; external surface is to the top. Many structural fiber bundles are oriented perpendicular to the bone surface within the cortex.