Use of Micro-Computed Tomography for dental studies in modern and fossil Odontocetes: potential applications and limitations

Teeth are important elements in studies of modern and fossil Cetacea (whales, dolphins), providing information on feeding habits, estimations of age and phylogenetic relationships. The growth layer groups (GLGs) recorded in dentine have demonstrated application for aging studies, but also have the potential to elucidate life history phenomena such as metabolic or physiologic events. Micro-Computed Tomography (Micro-CT) is a non-invasive and non-destructive technique that allows 3-dimensional study of mineralized tissues, such as human teeth, and their physical properties. Teeth from extant dolphins (Cetacea: Odontoceti) and some fossil odontocetes were scanned in a Skyscan 1172 Micro-CT desktop system. X-rays were generated at 100 kV and 100 mu A for extant samples, and at 80kV and 124 mu A for fossils. 0.5 mm thick aluminum and copper filters were used in the beam. Reconstructed images were informative for most extant species, showing a good resolution of the enamel layer, dentine and pulp cavity. Greyscale changes in the dentinal layers were not resolved enough to show GLGs. Visualization of the internal structure in fossil cetacean teeth depended on the degree of diagenetic alteration in the specimen; undifferentiated enamel and dentine regions probably reflect secondary mineralization. However, internal details were finely resolved for one fossil specimen, showing the enamel, internal layers of dentine and the pulp cavity. Micro-CT has been proven to be a useful tool for resolving the internal morphology of fossil and extant teeth of cetaceans before they are sectioned for other morphological analyses; however some methodological refinements are still necessary to allow better resolution of dentine for potential application in non-destructive age determination studies.