Mastodon tusk recovery

Abstract

The initial discovery of this large Mammut americanum tusk came on October 23 as two divers routinely trowelled sediments from within a 2 × 3 m grid about 6 m below the water surface. This excavation unit, known as Test F, level 23, was subsequently considered to be the lower part of stratigraphic Unit 3. The long axis of the tusk trended northward beyond the grid into the west bank of the river. In order to continue exposing the tusk, field protocol required that a new vertical excavation, 2 × 3 m, be opened immediately to the north of the tusk. This entailed a full day of additional work. The in situ tusk is pictured first in its discovery phase and secondly in its fully uncovered status on the river bottom (see Figs. 11.1 and 11.2). The sediments in which the tusk occurred consisted of massive clayey peat. Subsequent study of these peaty sediments showed that they were digesta of a large herbivore, most probably Mammut americanum. This mastodon digesta hypothesis and the constitution of the peat are fully discussed in Chapter 10 by Newsom and Mihlbachler. Seven closely corroborative carbon dates, based on four individual gourd seeds (Cucurbita pepo), two wood specimens, and a sample of bone collagen from the jugal of Palaeolama mirifica, all occurring in the digesta, gave an average uncalibrated date of 12,425 ± 35 14C B.P. (see Chapter 4 by Webb and Dunbar). A small sample of peat hand picked from the hollow end of the tusk and immediately submitted for an AMS date yielded a slightly older date of 12,940 ± 70. When the tusk was received on the riverbank and gently laid out in five adjacent sections, two striking features were noted. First, within about 5 min, the exposed surfaces of each successive piece changed color from light tannish orange to a dark chocolate brown. Presumably this represented oxidation of iron and other minerals present in the tusk dentin. The rate of color change beneath the surface of the tusk is unknown, but subsequent internal views a week later revealed approximately the same dark color. A second unexpected set of features was soon noted on the most proximal piece of the tusk. There was an elaborate set of grooves girdling one side of the tusk. It was also observed that this set of marks coincided with a subtle change from a darker colored region of tusk dentine to a lighter colored region nearer the proximal end. These features are evident in the close up picture of that region in Fig. 11.3. The color change evidently marked the distal end of the alveolar region of the tusk, where it had emerged from the premaxillary bone during the animal's life. This prompted the hypothesis that these circumferential grooves might be cutmarks delivered by Paleoindians removing the tusk from the skull. From that moment forward the ARPP was determined to investigate the question of whether this tusk might have been an object of human procurement.