that covered most of the body, and it persists today in a few taxa such as the coelacanth. Because dentin is softer than enamel, it wears away more quickly than enamel. Some mammalian teeth exploit this phenomenon, especially herbivores such as horses, deer or elephants. In many herbivores, the occlusal (biting) surface of the tooth is composed of alternating areas of dentin and enamel. Differential wearing causes sharp ridges of enamel to be formed on the surface of the tooth (typically a molar), and to remain during the working life of the tooth. Herbivores grind their molars together as they chew (masticate''), and the ridges help to shred tough plant material. A material similar to dentin forms the hard material that makes up dermal denticles in sharks and other cartilaginous fish. See also Dentinogenesis Dentinogenesis imperfecta Odontoblast Tooth development References External links Parts of tooth Tissues (biology)