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Estimating Cementum Annuli Width in Polar Bears: Identifying Sources of Variation and Error

Abstract Distinct annuli in cementum, a mineralized tissue surrounding the root of mammalian teeth, are used to estimate age in wildlife. Life-history information may be recorded in cementum patterns but interpretation is complicated by variation in cementum width between individuals, among their teeth, and around the surface of the root. First premolar teeth from polar bears (Ursus maritimus) were evaluated. We identified sources of variation in cementum growth and methods are presented that reduce error and permit comparisons within and between individuals. A minimum of 10 measurements from 1 aspect was required to produce precise estimates of cementum growth layer group (GLG) width. Variance component analysis revealed that comparisons between distal and mesial aspects of the root introduced the greatest variation among bears. Controlling for aspect, variance was partitioned differently between the mesial and distal surfaces. Comparisons between maxillary and mandibular premolars from the same bear indicated that data from these teeth should not be pooled; data collected from left and right lower premolars may be combined. Indices to represent adjusted GLG widths are described that reduce age and allometric effects, allowing life-history or environmental factors to be compared.