Patric, E.F. and W.L. Webb. 1960. An evaluation of three age determination criteria in live beavers. Journal of Wildlife Management, 24(1):37-44.

Abstract: The purpose of this paper is to evaluate three criteria for determining the age of live beavers. The three criteria to be examined are weight, the product of tail dimensions, and the breadth of the skull across the zygomatic arches. A real need exists for study of nearly all beaver aging criteria, because there is much disagreement in the existing literature concerning methods of beaver age determination. This lack of agreement is caused by the use of a great variety of aging criteria without a definite knowledge of their respective merits, and also by difficulties involved in attempting to secure marked animals of known age.