Pearson's coefficient of variation is in general not applicable in palaeontology, due to the heterogeneity of samples. The heterogeneity may be due to the mixing of two species, mixture of material from various biotopes, or from a relatively large time span. A new coefficient of variation is proposed, based on the range of the sample. This coefficient may be used to estimate the degree of variation of a sample, and to decide whether it is homogeneous. Its application is tested empirically on a large number of samples of cricetid molars from the European Tertiary.