Tracing the Source of the Elephant And Hippopotamus Ivory from ...

incisors”) of the elephant. Each tusk replaces a deciduous tooth called a ‘tush’ when the
elephant is six months to one year old. The tusks increase in size with age, although sex,
habitat, and the species will influence the size (Krzyszkowska 1990:33; Raubenheimer et
al. 1995: 571; Raubenheimer 1999: 57). In general, males have longer tusks than females
of the same age, and the circumference of the male tusk increases continuously, whereas
for the female the tusk ceases to grow in circumference when she reaches an age of 30-35
years (Layser and Buss 1985: 408-410). One researcher in Zambia, Elder (1970), was
able to identify correctly the sex of the elephant from 58 out of 60 tusks, based only on
the shape of the tusk (cited in Layser and Buss 1985: 407). Another reason for
differences in tusk size is that elephants are ‘right-tusked’ or ‘left-tusked,’ so that one
tusk is a working tusk and consequently made shorter through greater use (Krzyszkowska
1990:51).
The tusk itself has a tapering pulp cavity in the third closest to the elephant’s head
(the proximal end of the tusk). This end is also covered by ridged cementum. The tip (or
distal end) is solid and has a smooth outer surface (Krzyszkowska 1990: 33-34;
Raubenheimer 1999: 59; see Figure 1). Probably the most identifiable and diagnostic
marker of elephant ivory is the “engine-turning” pattern (short for “engine-turned
decussating appearance”) visible in transverse cross-sections of the tusk. This pattern is
also called “lines of Retzius,” as distinguished from the “lines of Owen” which are the
ovoid concentric rings spaced approximately 1 cm apart. Similar to tree rings, the lines
of Owen represent 6-8 years of tusk growth. The regular growth of the tusk is apparent in
such “lamellae” or laminations, which are the layers of dentine formation (see Figure 2).
10