Ground squirrels of the genus Marmota are known for their ability to tolerate bitterly cold climates, which they in part accomplish with their exceptional ability to hibernate for as much as eight months a year (Armitage et al., 2003). Most of the 15 living species are associated with montane habitats, and those that are not, like the North American woodchuck (Marmota monax) and the eastern European and central Asian bobak (M. bobak) inhabit regions with strongly seasonal climates and often bitterly cold winters (Armitage, 2000) (Figure 9.1). All marmots construct burrows, which can be more than one metre deep even in comparatively mild climates and as much as seven metres deep in the harsh climates of the Himalayas (Barash, 1989). During the cold phases of the last half of the Quaternary the fossil record demonstrates many marmots inhabited periglacial environments (Zimina and Gerasimov, 1973; Kalthoff, 1999). For these reasons, marmots are sometimes considered to be a quintessentially Quaternary clade, specialists on the cold variable climates that are unique to the past 2.6 million years of Earth's history. The world in which they originated, however, was very different; a warmer one in which there were no tundra biomes, no glacial–interglacial cycles, and no permanent ice cover in the Northern Hemisphere. In this chapter, we review the fossil and phylogenetic history of marmots, the palaeoenvironments in which they originated, and their relationship to glacial–interglacial cycles to better understand the contexts in which the specializations of this unique clade of rodents arose.
The Quaternary, the current geological period, is defined by the onset of permanent ice sheets in the Northern Hemisphere 2.58 million years ago and is by far the coldest period since the extinction of the last non-avian dinosaurs 65 million years ago (Zachos et al., 2001; Gibbard et al., 2010).