What material forms the external surface of walrus tusks, which lack enamel?

Dentin

Walrus tusks are anatomically classified as dramatically elongated upper canine teeth, and their composition is primarily dentin. A crucial aspect distinguishing them from many other dental structures is the notable absence of an external enamel coating. This means the primary hard substance making up the visible tusk structure is dentin. These energy-intensive structures evolved later in the lineage, likely driven by pressures such as sexual selection, dominance displays, or the utility of accessing benthic food sources beneath thick ice, suggesting a significant morphological investment that was not present in the initial members of the Odobenidae family.