RESEARCH ARTICLE Historical Biogeography and Body Form Evolution of Ground Squirrels (Sciuridae: Xerinae) D. Y. Ge • X. Liu • X. F. Lv • Z. Q. Zhang • L. Xia • Q. S. Yang Received: 24 December 2012 / Accepted: 30 July 2013 / Published online: 15 August 2013 Ó Springer Science+Business Media New York 2013 Abstract Xerinae is the most species-rich subfamily of the Sciuridae (Rodentia). This group of animals has a long complex evolutionary history, which witnessed severe environmental changes. In this paper, a comprehensive approach integrating information from fossil records, morphological, molecular and geographical data of extant species, and events of paleoclimate and paleogeography, were used to explore the evolutionary processes in the Xerinae. Xerinae probably originated in Eurasia around the early Oligocene, and dispersed to Africa via the Africa- Eurasia Land Bridge on two occasions during the Miocene, and subsequently evolved into the Protoxerini and African Xerini. The tribe Marmotini derived from a Eurasian ancestor and thrived in North America. Tamias re-occupied Eurasia in the early Miocene, while the distributions of Marmota and ‘Spermophilus’ genus-groups were restricted to North America at least until the late Miocene. Global cooling and the emergence of grass-dominated ecosystems from 15 Ma are likely to be the main causes for the radi- ation of Marmotini. The body form of Xerinae displays an allometric mode of evolution, with ground-living taxa, such as Marmota, Cynomys and Xerus notably enlarged, while Tamias has remained slim in body form. To cope with the global environmental changes, particularly the global cooling induced forest degradation and grassland expansion in the late Miocene, most Marmotini developed into true ground squirrels with short tails. The slim body adaptation in Tamias may be related to competition from tree squirrels, or their hoarding behavior, the latter helping them to cope with cold winter. Keywords Xerinae Á Phylogeny Á Evolution Á Historical biogeography Á Body form Introduction Xerinae, with 128 extant species, is the most species-rich subfamily in the Sciuridae (Thorington and Hoffmann 2005; Thorington et al. 2012). Xerinae includes the tribes Marmotini, Xerini and Protoxerini. Of these, most Mar- motini and all Xerini are ground squirrels wildly distrib- uted in the Northern Hemisphere and Africa, while Protoxerini are tree squirrels endemic to Africa (Fig. 1) (Thorington and Hoffmann 2005). Marmotini and Xerini live in burrows or amongst rocks, and tend to form colonies with complex social structure (Armitage 1981; Gouat and Yahyaoui 2001). This is distinct from Protoxerini, which are tree squirrels living alone or in pairs. The evolutionary history of these animals has been explored using both morphological characters and molecular data. Although morphological convergences have lead to numerous taxo- nomic controversies, particularly regarding the classifica- tion of ‘Spermophilus’ genus-groups (Harrison et al. 2003). This is a group including the extant species Notocitellus, Electronic supplementary material The online version of this article (doi:10.1007/s11692-013-9250-7) contains supplementary material, which is available to authorized users. D. Y. Ge Á X. Liu Á X. F. Lv Á L. Xia Á Q. S. Yang (&) Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences (CAS), Beichen West Road, Chaoyang District, Beijing 100101, China e-mail: yangqs@ioz.ac.cn X. Liu Graduate University of CAS, Yuquan Road, Beijing 100049, China Z. Q. Zhang Institute of Vertebrate Paleontology and Paleoanthropology, CAS, Xizhimenwai Street, Beijing 100044, China 123 Evol Biol (2014) 41:99–114 DOI 10.1007/s11692-013-9250-7