LAUSR

Abstract The Beringian Land Bridge is a well-documented dispersal corridor between the Eurasian continent and North America. Episodic sub-aerial exposure of the land bridge during the Late Cenozoic resulted from climatic oscillations and concomitant lowering of sea level. For much of the Pleistocene, dispersal was predominantly west-to-east (e.g., from Eurasia to North America), but a new discovery of the North American rodent Phenacomys from deeply buried sediments in The Netherlands documents an Early Pleistocene east-to-west invasion. The discovery reinforces earlier suggestive hints of an integrated Holarctic mammal fauna in the Early Pleistocene and provides a unique opportunity to establish a direct correlation of the classic mammal zonations of Europe and North America. Phenacomys is traditionally conceptualized as an endemic North American radiation of voles, and all extant taxa are exclusively North American. The first European remains of Phenacomys were recovered as part of the Zuurland Drilling Project from earliest Pleistocene (ca, 2.3–2.1 Ma) strata. The specimens were found in stratigraphic association with species that are well-known from more southern European assemblages of Early Pleistocene age, but also with contemporaneous taxa traditionally associated with more northern latitudes. The recognition of Phenacomys within the Zuurland assemblage demonstrates that the Bering Land Bridge served as a corridor for dispersal of mammal species during the earliest Pleistocene, and served as a physiographic mechanism for the integration of a circumpolar biogeographic province at that time.