Evolution of a dental character in the beaver Castor fiber L. (Mammalia: Rodentia)

Variation in morphology of beaver cheek teeth has been examined in respect of ontogeny, geographical variation and geological time. When the effects of ontogeny are taken into account, certain patterns of dental variation are found to be restricted in space and time. An isolated loop of enamel ubiquitously present in the lower third molars of European beavers from the present interglacial seems to be a “new” acquisition which is lacking in Recent Siberian and North American beavers, as well as in Western European specimens from earlier interglacials. Whilst the genetic basis of such morphological details is presumed rather than established, they may be helpful in tracing past population movements and are also of potential stratigraphic importance. Changes in range associated with Pleistocene climatic oscillations have led to the “sudden” appearance of this and other castorid dental characters in the Western European fossil record. The morphological discontinuity in the fossil record should be taken as evidence of climatic change rather than evidence for the operation of a certain pattern of evolution.