Wear-induced changes in the crown topography of molariform teeth have been widely used to index relative age in rodents. To assess the consistency of molar-wear estimates in natural populations of a sigmodont rodent (Bolomys lasiurus), we investigated the association between molar wear and two other age-dependent craniodental characters: degree of exposure of molar roots from the alveoli and ossification of the basisphenoid-basioccipital suture. We compared magnitudes of Spearman correlation coefficients among states of these characters in samples cross-classified by vegetation, season, and locality, under the null hypothesis of high correlation in the absence of differential environmental effects on molar wear. A bootstrap procedure was used to derive empirical sampling distributions of the age-index correlations and, thus, to establish realistic confidence intervals. We then employed a multivariate procedure to reduce subjectivity of classifying combinations of indices of age into age classes. Using a principal component analysis of the correlation matrix of craniodental indices, variation expressed among indices was summarized as a multivariate age factor. An objective ordering of sets of indices of age (the various combinations of tooth-wear, molar-root exposure, and suture-ossification conditions observed among all samples) was provided by projecting individuals onto the first principal component. The method revealed age-frequency differences between wet- and dry-season samples from northeastern Brazil, ostensibly due to the occurrence of a reproductive peak at the beginning of the rainy season, and predicted a maximum life span for B. lasiurus of ca. 1-1.5 years in the wild.79411701183Almeida, C.R., Almeida, A.M., Brasil, D.P., Observations sur le comportement de fouissement de Zygodontomys lasiurus pixuna Moojen, 1943 (1981) Mammalia, 45, pp. 415-421. , Reproduction au laboratoire (Rongeurs, Cricétidés)Child, D., (1990) The Essentials of Factor Analysis. Second Ed., 120p. , Cassell Educational Limited, London, United Kingdom(1972) Observações Pluviométricas No Nordeste do Brasil, , Ministério do Interior, Departamento Nacional de Obras Contra as Secas, Rio de JaneiroEfron, B., Tibshirani, R.J., (1993) An Introduction to the Bootstrap, 436p. , Chapman and Hall, New YorkDe Francisco, A.L., Magnusson, W.E., Saniotti, T.M., Variation in growth and reproduction of Bolomys lasiurus (Rodentia: Muridae) in an Amazonian savanna (1995) Journal of Tropical Ecology, 11, pp. 419-428Gintlis, R.V., A study on the age estimation in Meriones erythrourus Gray (1959) Bjulleten Moskovskago Obscestva Ispytateles Prirody, Otdel Biologisceskij, 64, pp. 23-30Gower, J.C., Some distance properties of latent root and vector methods used in multivariate analysis (1966) Biometrika, 53, pp. 325-338Hjorth, J.S.U., (1994) Computer Intensive Statistical Methods: Validation, Model Selection and the Bootstrap, 272p. , Chapman and Hall, London, United KingdomJöreskog, K.G., Wold, J., (1982) Systems under Indirect Observation: Causality, Structure, Prediction, 337p. , North-Holland Publishing Co., Amsterdam, The NetherlandsJunge, R., Hoffmeister, D.E., Age determination in raccoons from cranial suture obliteration (1980) The Journal of Wildlife Management, 44, pp. 725-729Kaufman, L., Rousseeuw, P.J., (1990) Finding Groups in Data: An Introduction to Cluster Analysis, 342p. , John Wiley & Sons, New YorkKruskal, J.B., The relationship between multidimensional scaling and clustering (1977) Classification and Clustering, pp. 17-44. , J. Van Ryzin, ed.. Academic Press, New York, 467 ppKrzanowski, W.J., Marriott, F.H.C., (1994) Multivariate Analysis. Part 1: Distributions, Ordination and Inference, 280p. , Edward Arnold, London, United KingdomManly, B.F.J., (1997) Randomization, Bootstrap and Monte Carlo Methods in Biology. Second Ed., 399p. , Chapman and Hall, London, United KingdomMorris, P., A review of mammalian age determination methods (1972) Mammal Review, 2, pp. 69-104Nelder, J.A., A simple algorithm for scaling graphs (1976) Applied Statistics, 25, pp. 94-96Nimer, E., (1989) Climatologia do Brasil, 421p. , Instituto Brasileiro de Geografia e Estatística, Rio de JaneiroPankakoski, E., An improved method for age determination in the muskrat, Ondatra zibethica (1980) Annales Zoologici Fennici, 17, pp. 113-121Parreira, G.G., Cardoso, F.M., Seasonal variation of the spermatogenic activity in Bolomys lasiurus (Lund, 1841) (Rodentia, Cricetidae) from southeastern Brazil (1993) Mammalia, 57, pp. 27-34Pearson, O., La estrutura por edades y la dinamica reproductiva en una población de ratones de campo, Akodon azarae (1967) Physis, 27, pp. 53-58Pearson, O., Martin, S., Bellati, J., Demography and reproduction of the silky desert mouse Eligmodontia in Argentina (1987) Fieldiana: Zoology, 39, pp. 433-446Reig, O., A proposed unified nomenclature for the enamelled components of the molar teeth of the Cricetidae (Rodentia) (1977) Journal of Zoology, 181, pp. 227-241. , LondonAn assessment of the systematics and evolution of the Akodontini, with the description of new fossil species of Akodon (Cricetidae: Sigmodontinae) (1987) Fieldiana: Zoology, 39, pp. 347-399Rohlf, F.J., Slice, D., Extensions of the Procrustes method for the optimal superposition of landmarks (1990) Systematic Zoology, 39, pp. 40-59(1990) SAS/IML Software: Usage and Reference, Version 6, 501p. , SAS Institute, Cary, North Carolina(1990) SAS/STAT User's Guide, Version 6, 1682p. , SAS Institute, Inc., Cary, North CarolinaStrauss, R.E., On allometry and relative growth in evolutionary studies (1987) Systematic Zoology, 36, pp. 72-75Streilen, K., The ecology of small mammals in the semiarid Brazilian caatinga. IV. Habitat selection (1982) Annals of Carnegie Museum, 51, pp. 331-343(1992) Matlab User's Guide, 223p. , The Mathworks, Inc., Natick, MassachusettsVeiga, T., Epidemiologie de la peste au Nord-Est du Brésil: Facteurs phytogéographiques et climatiques responsables de la dynamique de population des rongeurs (1981) Mammalia, 45, pp. 289-298Voss, R.S., Marcus, L.F., Escalante, P.P., Morphological evolution in muroid rodents. I. Conservative patterns of craniometric covariance and their ontogenetic basis in the neotropical genus Zygodontomys (1990) Evolution, 44, pp. 1568-1587Young, F.W., Hamer, R.M., (1987) Multidimensional Scaling: History, Theory, and Applications, 317p. , Erlbaum Associates, Hillsdale, New JerseyZar, J.H., (1996) Biostatistical Analysis. Third Ed., pp. x+916p. , Prentice-Hall, New York