Mihok, S. (1980) Ageing young Clethrionomys gapperi with M2 tooth characteristics. Canadian Journal of Zoology 58, 2280-2281.

Groove closure of the second upper molar of Clethrionomys gapperi occurs at an age of 32 to 35 days and measurable roots form at an age of 62 to 72 days. Tooth measurements are relatively good estimators of age in open-groove and immature, closed-groove age-classes, but are poor estimators of age in mature, closed-groove age-classes.