Tusk metrics and pair symmetry in savannah elephants

Abstract

The right and left tusks and from both genders from five separately culled savannah elephant clans were measured, recording weight (n = 2,453), overall length (n = 563), external length beyond the gingivae (n = 158), internal length within the alveolus (n = 158) and circumference at the lip (n = 158).  The increase in tusk weights and lengths with age was reconfirmed as basically exponential in males and more linear in females up to their fifth decade. Between the right and left tusks, the five metrics were on average symmetrical (in the sense of being mirror images of one another), and predictive of both age and each other (i.e. from one the others can be deduced). Strikingly, however, pair length symmetry is less between within alveoli, where growth takes place, than between their corresponding external parts, where tusks are essentially dead tissue. Such greater external symmetry can only occur if the shorter tusk grows faster to catch up with its partner or the longer tooth is reduced through wear towards parity with its partner, or both.