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  • Print publication year: 2015
  • Online publication date: August 2015

8 - Themes and variation in sciurid evolution


Introduction: Themes emerge from variation in the Sciuridae as a group, a taxon and a clade

With a species diversity approaching 300 (Thorington and Hoffmann, 2005) and nearly worldwide in their distribution, squirrels are common and important elements of many ecological communities. The diurnal habits of most taxa together with their relative conformity in body plan make them familiar and easily recognized by both scientists and non-specialists.

The squirrel family, Sciuridae, also has a long history of recognition by taxonomists as a coherent grouping, despite its comprising distinctive forms associated with use of different locomotor substrates (Table 8.1). At times, burrowing or gliding forms have been separated from the archetypal arboreal squirrels: Fischer de Waldheim (1817), the authority credited for naming the Sciuridae (Thorington and Hoffmann, 2005), advocated use of limb structure in recognizing groups of mammals, and accordingly, he removed flying squirrels (‘Petauristus’, Fischer de Waldheim, 1817: p. 422) to another ‘Division’ apart from ‘Familia Sciuriorum’ (p. 408), even though Linnaeus had placed flying squirrels together with tree and some ground squirrels under SCIURUS (Linnaeus, 1758: pp. 63–64; see Table 8.1). Woodchucks and marmots have also posed something of a problem, to Linnaeus (1758:p. 60), who listed them under ‘MUS’, and to many subsequent authors who also set them apart from other sciurids. However, by late 1839 (according to Brandt, 1855: p. 106, and Alston, 1876: p. 62) all of these animals had been combined by Waterhouse to form a version of Sciuridae that would be congruent with the modern concept of the family. Along the way, dormice (referred to as ‘Myoxus’) have often crept into lists of squirrels (e.g. Fischer de Waldheim, 1817, but not those of Linnaeus before him or Brandt subsequently), both their exclusion and their inclusion foreshadowing current views based on molecular evidence that dormice are distinct from sciurids but have closer affinities with them (plus aplodontids) than with other rodent families (e.g. Blanga-Kanfi et al., 2009; Churakov et al., 2010; Fabre et al., 2012).

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Evolution of the Rodents
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