The present work describes the morphological distance of a cranium between specimens of Castor fiber from Neolithic period and contemporary specimens which live in the same region of Poland. Two well-preserved skulls of Neolithic beavers and 32 skulls of contemporary beavers were available. In order to compare the skulls, first the age of the animals was estimated followed by 22 measurements of each skull. On the basis of Principal Components Analysis it was found that the skull in the beaver changes its dimensions with age. Moreover, a strong positive allometry was found of the external sagittal crest in relation to age. The other craniometric features showed negative allometry. The PCA method also made it possible to determine that the skull of a 3-year old Neolithic beaver is as big as skulls of 4- to 5-year old contemporary ones. The skull of the second Neolithic beaver, a 5-year old, is the largest among skulls of contemporary beavers in its age group.