conodont, or small fossil that is toothlike in form and structure, that has a prominent, centrally located denticle flanked on either side by smaller, less pointed denticles. In some forms the row of denticles may be straight, whereas in others it is curved. Ozarkodiniforms are especially useful as index, or guide, fossils in studies of the Silurian Period (444 million to 416 million years ago).