Specific teeth are needed to do age analysis, depending on the species. The lower premolar 4, shown here, is the tooth for fishers and similar small narnivores. Credit: Matson's Lab—Courtesy Sign up ...

Matson finds those rings just inside the roots of the tooth in a layer called the cementum. Peering through a high-powered microscope, Matson and others at his laboratory spend long hours carefully ...