Holarctic evolution and dispersal of squirrels (Rodentia: Sciuridae) [Evolution holarctique et dispersion des ècureuils].

Résumé

Conclusions : 1- Members of the Sciuridaefirst appear in North America during the early Oligocene. 2- By the mid-Oligocene, sciurids are found in Europe and North America and both ground squirrels and tree squirrels had evolved by the late Oligocene. 3- Probably as a result of differing depositional environments, the European squirrel record is dominated by flying squirrel remains, while that in Nort America shows a predominance of terrestriel squirrel types. 4- One, and possibly, two lineages of terrestrial squirrels entered Europe from North America in the teriary but each became extinct. 5- Modern ground squirrels, genus Spermophilus, and marmots, genus Marmota, entered Eurasia in the latest Pliocene or early Pleistocene from North America. 6- Chipmunks, genus Tamias, entered Asia from North America in the middle Pliocene. One or two lines may have reinvaded Noth America in the early Pleistocene or chipmunks may have evolved independently in the Nearctic and Palearctic since mid-Pliocen time. 7- Tree squirrels, genus Sciurus, sensu latissimo, are known in both North America and Eurasia since the Miocene. The center of orgin for modern Sciurusis unknown. 8- North America has been the center of terrestrial squirrel radiation since the origin of the family.