Mise en place et évolution au coursdu Cénozoïque des stratégies adaptatives des castoridés (Mammalia, rodentia)

As early as the Miocene basis, Steneofiber, an European Castorid genus, evidenced a reproductive strategy similar to that of the extant Castor: a two-years long breeding pattern. At the same time, in North America, a group of burrowing Castorids flourished and some of them dug helicoidal burrows (Daimonelix) with a basal living chamber in which the youngs were raised. The fossorial branch of Castorids disappeared at the end of the Lower Miocene but the aquatic one continued until now with periodic radiations that seem to be related to palaeogeographic changes. In the other families of Oligocene rodents, the hypothesis concerning the relationship between the value of the D4/P4 length ratio and the life-history strategies is discussed; our current knowledge seems to be too fragmentary to draw valuable conclusions.