Premolar Cementum and Noncementum Lengths 



As Potential Indicators of Age for Beavers, 



Castor canadensis (Rodentia: Castoridae) 



Allan E. Houston 



Ames Plantation, Agricultural Experiment Station, The University 



of Tennessee, P. O. Box 389, Grand Junction, Tennessee 38039-0389 



AND 



Michael R. Pelton 



Department Forestry, Wildlife, and Fisheries, The University 



of Tennessee, Knoxville, Tennessee 37901-1071 



ABSTRACT — Jaws from 28 beavers (Castor canadensis), >4 years 

 old as determined from cementum annuli on premolars and 

 molars, were collected in west Tennessee. An exponential model 

 predicting age was developed based on the independent vari- 

 ables cementum length and noncementum length as measured 

 along the estimated, maximum longitudinal centerline of cross- 

 sectioned premolars: AGE = + 6.1784 * e ( : o.io3i*noncemen) + 



2 6513 * e (0.1U9*CEMENTUAf) 



Several methods of aging beavers have been attempted with varying 

 degrees of accuracy, including pelt size (Buckley and Libby 1955), 

 tail dimensions, total body mass, skull measurements (Patric and Webb 

 1960), and baculum size and mass (Friley 1949). Probably the most 

 accurate method was developed by van Nostrand and Stephenson (1964) 

 using tooth eruption and closure of basal openings of premolars and 

 molars for beavers up to 3 years old, and cementum layering in premolars 

 and molars for specimens >4 years. Larson and van Nostrand (1968) 

 further refined this technique to include criteria dealing with cementum 

 deposition around basal openings. They noted that age estimations 

 may be complicated by multi-annual cementum layering, but that the 

 ratio of cementum to noncementum on molars and premolars might 

 be used to estimate age in older specimens. 



Our objective was to use premolar cementum length (aggregate 

 of all annual cementum depositions) and noncementum length (remains 

 of the original tooth) as independent variables to evaluate a model for 

 estimating age of beavers >4 years. 



Brimleyana 22:67-72, June 1995 67 



