The Microstructure of Proboscidean Ivory and its Application to the Subordinal Identification of Isolated Ivory Specimens

Abstract

Though relatively common as fossils, isolated proboscidean ivory fragments are difficult to identify below the ordinal level because of their lack of diagnostic gross morphological features. To help rectify this situation, the microstructure of ivory from a wide variety of proboscideans was surveyed, including Zygolophodon, Mammut (family Mammutidae), Gomphotherium, Cuvieronius, Rhynchotherium, Amebelodon, Torynobelodon (family Gomphotheriidae), Elephas, Loxodonta, and Mammuthus (family Elephantidae). On the basis of this survey, the following discoveries were made. 1) Medullar and cortical ivory of mammutids have microstructural features that allow them to be readily distinguished from those of gomphotheres and “typical” elephantids. 2) Gomphotheres and extant elephantids have identical medullar and cortical ivory. 3) Mammuthus medullar ivory is identical to that of extant elephantids and gomphotheres, but its cortical ivory strongly resembles that of mammutids; the two can be distinguished only by subtle features of the dentinal tubules. On the basis of these survey results, practical aspects of identifying isolated ivory fragments are discussed, as well as the evolutionary implications of observed ivory microstructural patterns.