Keywords: 
• zoology /
• Xerinae /
• origin /
• evolution /
• review

Abstract: The origin and evolution of Xerinae, a subfamily of squirrels, were chronicled revealing that their high biodiversity and wide distribution were due to the Africa-Eurasia Land Bridge and the Bering Land Bridge which facilitated dispersal and adaptive radiation. Both fossil and molecular evidence showed that Xerinae originated in Eurasia around the early-Oligocene epoch and soon evolved into three clades. Clade 1 dispersed to Africa via the Africa-Eurasia Land Bridge when it was first formed about 19 million years （Ma） ago. Since there was no competition from tree squirrels, Clade 1 gradually evolved into the Protoxerini. Clade 2 dispersed to Africa with the second formation of the Africa-Eurasia Land Bridge about 14 Ma evolving into Atlantoxerus and Xerus. Clade 3 was the ancestor of the Marmotini tribe; it evolved into Sciurotamias in Eurasia and simultaneously dispersed to North America via the Bering Land Bridge around the mid-Oligocene epoch. Following emergence of grass-dominated ecosystems in North America, this clade evolved into Tamias, Spermophilus, Marmota, and Cynomys. Tamias, Spermophilus, and Marmota re-occupied Eurasia in the Miocene period, and then Spermophilus and Marmota underwent their adaptive radiation in Eurasia. Xerinae thrived mainly because of morphological and behavioral variations that aided in adaptation to environmental change. During this course of evolution, ground dwellers like Marmota, Cynomys, and Spermophilus developed larger bodies with shorter tails; whereas, forest dwellers maintained slim bodies with relatively longer tails. ［Ch, 2 fig. 53 ref.］