Age Determination of Grizzly Bears from Fourth Premolar Tooth Sections

Craighead, John; Craighead, Frank; Mccutchen, Henry

The cementum-layer aging technique was tested for grizzly bears (Ursus arctos) by comparing the deposition of dark-staining and light-staining layers in the lower fourth premolars of 12 grizzlies, 9 of which were known- or established-age. The phenomenon of cementum layering in P4 appeared to persist throughout the life of the grizzly bear. Extracting premolars in alternate years revealed that one wide, light-staining and one narrow, dark-staining layer was deposited during each year of life. The annuli became progressively more difficult to count in older bears and separate annuli can not always be traced around the entire tooth. Individual variation was evident, but the light zones were largely formed during July, August, and September. Deposition of this layer began in May or June when bears weighed the least. The dark layer was not generally evident until late fall and sometimes was not well-defined in April. Thus it appeared that formation of the dark layer may extend from early autumn to May. There appeared to be no relationship between deposition of the dark cementum layer and low nutrition because bears remained in good physical condition throughout fall and winter. The first five annuli are wider than subsequent annuli. This phenomenon may be correlated with physical maturation and cessation of rapid growth.

Age Determination of Grizzly Bears from Fourth Premolar Tooth Sections

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