Abstract
Materials are a tusk of a young Indian elephant (Elephas maximus LINNÉ) without any abrasion on its surface, and molars of Moeritherium and Palaeomastodon. The inside and outside of the tip of the tusk are covered with a thin enamel layer and a thin cemenuum layer, respectively.
On the tusk, a histological examination by light-and scanning electron-microscopy has revealed some different characteristics from those of the molar teeth. Hunter-Schreger's bands are developed in the inner two-third of the enamel layer, though the outer one-third is a prismless enamel layer with distinct Retzius lines. Schreger's bands of the enamel form more regular rows in the tusk than in the molar teeth. Each band is some 30-Em wide and is composed of 10-15 enamel prisms in a parazone. The enamel prism is 4-5μm in diameter and shows a key-hole pattern similar to that of human teeth. Ginkgo leaf patterns characteristic of the Elepas molar enamel can not be observed in the tusk enamel. Processes of dentinal tube of several μm in length are there in the enamel layer just adjacent to the dentino-enamel junction, though no large enamel spindles are observed.
The enamel of Moeritherium and Palaeomastodon has the key-hole pattern of enamel prism and well developed Hunter-Schreger's band same as the Mastdon.
The histological features of the Indian elephant tusk enanel are similfar to those of the molar enamel of Moeritherium. Palaeomastodon, Mastdon and Stegodon, which is supposed to be an ancestral genus of Elephas.
