Sigmodontines (Rodentia: Cricetidae), the largest living radiation of Neotropical rodents (90 genera, 489 species), show about 10% having specializations related to a semiaquatic habitat. In addition, this mode of life is unequally distributed among the several clades which compose the subfamily, concentrated in the Ichthyomyini and in a few large-bodied Oryzomyini. The observed taxonomical and geographical pattern is here discussed in a biogeographical historical context. As working hypothesis is advanced that the risk of predation (exerted by animalivorous fresh-water vertebrates) shaped and limited since the late Miocene the semiaquatic performance of the subfamily. Moreover, by exploring the fossil record can also be argued that during the Pleistocene is registered an important number of amphibious sigmodontines extinctions. Therefore, the scarcity of living semiaquatic sigmodontine rodents can be attributed to a combination of an undervalued habitat (mostly by risk of predation) plus a recent pauperization (by a sum of biological extinctions) of the members of that guild. A shallow comparison of the sigmodontine case against murids suggests that continental waterbodies resulted partially refractory to muroid colonizations.