TRIBAL people FIG. 5 (top): Harpoon or specimen. Aleut, Aleutian Islands, Alaska. Likely fi rst half of the 19th century. Narwhal tusk. L: c. 175 cm. Inscribed: “Horn of the narwhal, Barrow Collection” and “Presented to Mr. Barrow by Captain Penny.” Ex John Barrow, collected by Captain William Penny before 1855. British Museum, London, inv. Am1855,1126.36. © The Trustees of the British Museum. FIG. 6 (above middle): “The Swimming Reindeer.” Late Magdelenian, Montastruc, France. 11,000 BC. Mammoth ivory. L: 20.7 cm. Excavated by and museum purchase from Peccadeau de l’Isle, 1887. British Museum, London, inv. Palart.550. © The Trustees of the British Museum. Canada, Siberia, and Alaska (fi gs. 7, 8, 12a).17 Pacifi c walrus teeth average approximately 5 cm in length and have been carved into smaller art objects and engraved as scrimshaw art. However, the prominent tusks of the walrus are most often sought. These tusks, which are extended upper canine teeth protruding downward from the mouth, can reach a length of nearly 1 meter in both males and females. In analyzing a cross section of a walrus tooth (as opposed to the tusks), a thick layer composed of rings of cementum is readily apparent. Unlike other species, a well-defi ned and somewhat rounded transitional ring between the cementum and the inner dentin is detected. 18 Over time, the structure and composition of a walrus tooth changes, and the pulp cavity fi lls in with secondary dentin as the walrus ages (fi g. 4c). A prominent feature that identifi es ivory carvings in walrus tusk is the naturally occurring longitudinal breathing cracks that manifest as thin black lines. Caused by abrupt changes in temperature that the walrus regularly experiences while transitioning from icy waters to sun-spattered rocks, these distinctive lines run the length of the tusk and are most easily seen in cross section.19 They can penetrate the cementum and on some occasions run into the dentinal layers. Another unique feature of walrus tusk is the structure of the tooth itself. The enamel layer of the canine tusk is ordinarily between 9–13 mm thick, irrespective of sex, but the core of female ivory is smaller in comparison to the core of male ivory. The secondary dentin in the pulp cavity of both is deposited irregularly and appears crystalline, somewhat resembling oatmeal (fi g. 4d). Adult female walrus canine tusks usually occupy a weight range of between .75 to 1 kg, while adult male tusks usually weigh 2 to 3 kg, although on rare occasions they can exceed 4.5 kg.20 The coloration of walrus ivory can be anywhere between creamy and near black, depending on the conditions in which it has been preserved. For archaeological items, this is determined by the time it has been exposed to external environmental factors and the type and composition of the soil it has lain in contact with.21 Blackened ivory comes from brownish-black organic soil, while the brownish- or orange-colored material is excavated from iron-stained sandy or gravelly soils. Cross sections of dentin from both elephant and mammoth ivory also display uniquely characteristic crosshatchings formed by dentinal tubules that make uniform lines layered throughout the dentin, which are known as Schreger lines. Microscopic analysis of these allows for identifi cation of the source animal, since the angles of intersection are specifi c to each species.15 The angles of the Schreger lines in the outer layers of the dentin in mammoth tusks are acute, less than 90 degrees (fi g. 4b), whereas those comparably arrayed in modern-day elephant tusks are obtuse, greater than 90 degrees (fi g. 4a). This analysis should be based upon multiple angle measurements and calculated using the average of the results. Proboscidean molars also occasionally occur in art, most commonly in Indonesia, and have a distinctive striated pattern. Ancient examples are often partially fossilized and are generally referred to as mammoth, although the source may be elephant (fi g. 12d). The distinction between modern elephant and ancient proboscidean ivory is critical due to the fact that the sale of extinct proboscidean ivory is subject to relatively few restrictions, while the importation and exportation of elephant ivory is tightly regulated. WALRUS Odobenus rosmarus Walrus populate the Arctic Ocean, a relative narrow geographic band centering around the North Pole.16 The walrus is a prized source of ivory that is an invaluable component of indigenous material culture and artwork, particularly in—though not limited to—Greenland,
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