Determining the species source of prehistoric ivory
By Dr. Joan Herrera
Paleoindians hunted mammoths and mastodons here in Florida over 12,000 years ago. They made tools from the ivory of these animals, most notably a spearlike tool. This tool is commonly referred to as an ivory foreshaft, but recently there has been much debate about its actual purpose.
Although the Paleoindians are known to have hunted both mammoths and mastodons, it is thought that they may have had a preference for using mammoth ivory as the material for making shafts. It is not known if there was a cultural basis for this preference, or if it was due to some property of the material. Whatever the reason, it will be remarkable if a significant number of the ivory tools that we test are made of mammoth ivory. While mammoths were more common farther north, in the regions from which the Paleoindians probably migrated, mastodons appear to have been much more prevalent here in Florida.
The proboscidean species from which a piece of tusk came can be determined by looking at the pattern of dentin tubules spiralling through the ivory. This feature of the dentin is the “Schreger pattern”, and each species has a distinctive herringbone pattern (see photograph).
The Schreger pattern is made up of alternating bands of dark and light material forming convex spiralling tracts through the ivory. There are elements in the pattern that spiral to the left and others spiral to the right. By measuring the angle formed by tangents drawn to the left-facing and right-facing curves of the spirals, Dan Fisher (University of Michigan) and his colleagues have quantified a significant species difference between mammoths and mastodons in these intersection angles. Fisher found that the Schreger pattern angles of mastodons average about 124.7 degrees, and those of mammoths average 87.1 degrees. By measuring these angles in the dentin of the ivory foreshafts in our collection we hope to determine the species from which each foreshaft was made, and to discover if the Paleoindians did have a species preference for the source of the ivory for their toolmaking.
The information gained from measuring the Schreger patterns in the ivory foreshafts in the Florida Museum of Natural History collection will be added to other data from electron microscope studies and will be analyzed, presented, and published by Dr. S. David Webb, James Dunbar, and Andy Hemmings in their studies of worked ivory.