Paleogene rodents of Eurasia

Soon after their Asian origin in the Late Paleocene, rodents began a morphological radiation and geographic expansion that extended across the entire Holarctic and at least northern Africa. Following this initial dispersal, a relatively high degree of endemism developed among Eocene rodents of both Europe and Asia. Only the family Ischyromyidae was shared by Europe and Asia, but the ischyromyid genera of the two areas were highly divergent. Eocene endemic development appears to have been complete among the glirids and theridomyids of Europe and the ctenodactyloids of Asia. The evolution of Cylindrodontidae, Eomyidae, Zapodidae, and Cricetidae in Asian Eocene faunas occurred independently of contemporary rodent faunal developments in Europe. Following the latest Eocene or early Oligocene regression of the marine barrier between Europe and Asia, marked faunal changes occurred as a result both of the evolution of new rodent families (e.g., Aplodontidae, Castoridae, Sciuridae) that accompanied climatic changes of the later Eocene and of changes in rodent distribution across the Holarctic. Within Europe, the theridomorphs were at last negatively impacted, but the glirids appear not to have been adversely affected. In the Asian Oligocene, the ctenodactyloids continued to be a prominent part of rodent faunas, although they were diminished in morphologic diversity.