Abstract
Enamel of several fossil and recent arctoid carnivores was studied with light and scanning electron microscopy. As in other carnivorans, 3 types of Hunter–Schreger bands (HSB) were observed: undulating, acute-angled, and zigzag HSB, which differ in their 3-dimensional complexity. Data on arctoid carnivores were used to test the hypothesis that zigzag HSB evolved multiple times to resist cracking of the enamel under high tensile stress. Distribution of HSB, except presence of zigzag HSB in the herbivorous panda, Ailuropoda, supported the hypothesis.