Shrews form a coherent group which leaves little doubt about its monophyly. One problem still under discussion is the inclusion or exclusion of the extinct Heterosoricinae Viret and Zapfe, 1951. Many authors include them in Soricidae as a subfamily (Engesser, 1975; Jammot, 1983; McKenna and Bell, 1997; Repenning, 1967; Storch and Qiu, 1991; Storch et al., 1998), others prefer family level for the Heterosoricinae (Harris, 1998; Reumer, 1987, 1998; Rzebik-Kowalska, 1998). If one compares the concepts expressed by Repenning (1967), Gureev (1971, 1979), Jammot (1983), George (1983), Reumer (1987, 1998), or Hutterer et al. (2002b), the subfamiliar and tribal subdivision of the Soricidae is not well resolved. Here I adopt a slightly modified system which is principally based on Reumer (1998). A strict phylogenetic classification however could include all extant shrews within a subfamily Soricinae, with Crocidurini, Myosoricini, and Soricini as tribes (Hutterer et al., 2002b; Stanley and Hutterer, 2000). Recognition of these three clades is supported by allozyme data (Maddalena and Bronner, 1992) and by RNA sequence data (Querouil et al., 2001). Yet, for practical reasons, I retain these clades at the subfamily level and use tribal subdivisions where appropriate. Lopatin (2002) recently named another new subfamily Soricolestinae for "the earliest and most primitive shrew" from the Middle Eocene of Mongolia.
Family-wide reviews are available on natural history (Churchfield, 1990), hair structure (Ducommun et al., 1994), external morphology (Hutterer, 1985), dental adaptations (Dannelid, 1998), and chromosomal evolution (Zima et al., 1998), protein evolution (Ruedi, 1998), life histories and energetic strategies (Innes, 1994; Taylor, 1998), and social systems (Rychlik, 1998). Congress volumes of interest covering a wide array of aspects include Findley and Yates (1991), Merritt et al. (1994), Zima et al. (1994), Hanski and Pankakoski (1998), and Wojcik and Wolsan (1998). Conservation aspects are dealt with in the IUCN action plans for Africa (Nicoll and Rathbun, 1990) and Eurasia (Stone, 1995). All African shrew species were re-assessed in January 2004 at a Global Mammal Assessment workshop in London, resulting in new IUCN ratings for many species. For the most current conservation status, the reader should consult the IUCN website (www.redlist.org).
The fossil history of shrews was reviewed by Repenning (1967) and Reumer (1994, 1995); excellent regional reviews cover Africa (Butler, 1998), Asia (Storch et al., 1998), Europe (Rzebik-Kowalska, 1998), and North America (Harris, 1998; see also Hutchison and Harington, 2002). Asher et al. (2002) convincingly identified the Eocene Parapternodontidae as the sister taxon of the Soricidae. Some genetic studies suggest a closer relationship of shrews to bats (e.g., Narita et al., 2001), but these studies did not include relevant fossil taxa identified by Asher et al. (2002). The earliest remains of shrews are known from the Eocene of North America (Harris, 1998), Oligocene of Eurasia (Rzebik-Kowalska, 1998; Storch et al., 1998), and Miocene of Africa (Butler, 1998). Presumedly older taxa such as Cretasorex (Nesov and Gureev, 1981) from the Upper Cretaceous of Uzbekistan and Ernosorex (Wang and Li, 1990) from the Eocene of China were assigned to this family, but the first was probably based on a contaminant (Nessov et al., 1994), and the second subsequently transferred to the family Changlelestidae (Tong and Wang, 1993). Fossil shrews are known from the High Arctic in the north (Hutchison and Harington, 2002) to South Africa in the south (Butler, 1998). The fossil and recent diversity is highest in Africa, Eurasia, and North America, but northern South America and the Indomalayan Region also house a rich, though younger radiation.
Illustrated textbooks or reviews are available for a number of larger geographical units, such as North America (Hall, 1981; Wilson and Ruff, 1999), Europe (Mitchell-Jones et al., 1999; Niethammer and Krapp, 1990), Russia (Nesterenko, 1999; Yudin, 1989), Japan (Imaizumi, 1970), Arabia and Asia Minor (Harrison and Bates, 1991; Kryštufek and Vohralík, 2001), Pakistan (Roberts, 1997), the Indomalayan Region (Corbet and Hill, 1992), or southern Africa (Mills and Hes, 1997; Smithers, 1983). Sources for common names are Wolsan and Hutterer (1998) and Wilson and Cole (2000).