ENAMEL MICROSTRUCTURE OF PAKICETUS (MAMMALIA, ARCHAEOCETI)

The tooth enamel of the earliest cetacean, Pakicetus, is described and compared to enamel of a primitive artiodactyl and a variety of primit ive ungulate families. Pakicetus enamel organization, which is conside red primitive for Cetacea, consists of a combination of radial and dec ussating enamel types. Prism patterns include prisms with open (horses hoe-shaped) and closed (circular) boundaries. Pakicetus enamel is simi lar to that of many primitive ungulates, including Diacodexis, the ear liest artiodactyl, and Mesonychidae, an archaic ungulate family that o ften is considered close to the ancestry of Cetacea. This finding is c onsistent with the hypothesis, originally proposed on the basis of oth er aspects of morphology, that artiodactyls, cetaceans, and Mesonychid ae are closely related.