Scanning electron microscopic search for peritubular dentine in some early perissodactyls

A scanning electron microscopic study has shown the presence of a typical layer of peritubular dentine in Hyrachyus. An homogeneous ring-shaped layer in continuity with intertubular dentine and considered as peritubular dentine despite its acid resistant character was observed around the lumens of dentinal tubules in Protungulatum, Tetraclaenodon and Propachynolophus maldani teeth; there is some evidence that the acid solubility of peritubular dentine has been altered during fossilization. No peritubular dentine was found in Phenacodus, Hyracotherium or Homogalax.