Simpson (1945) deemed Myoxidae Gray, 1821 invalid due to the apparent synonymy of the type genus Myoxus Zimmermann, 1790, with Glis Brisson, 1762, and used Gliridae Thomas, 1896. Hopwood (1947) argued that Brissonís names are invalid because they are not Linnaean or binomial, and noted that Glis is valid in Erxleben (1777) for marmots, ground-squirrels, voles, and lemmings, rendering Glis Storr, 1780 (which included pedetids, dormice, and other rodents) invalid. Thus the oldest available name to replace Glis Brisson is Myoxus Zimmerman, valid in Linnaeus (1788) for dormice, and, but for the ruling discussed below, the correct family name for dormice would be Myoxidae. Despite this clear historical evidence given in support of recognizing Myoxidae as the valid family name for dormice (see also Wahlert et al., 1993), and despite the willingness of many dormouse experts to employ Myoxidae as the valid family name (Hutterer, 1996; and usage of Myoxidae in Filippucci, 1995), the unfortunate ruling by the International Commission on Zoological Nomenclature (1998) to conserve Glis Brisson requires that the valid family name for dormice is henceforth Gliridae.
Glirids are one of the oldest extant rodent families. They first appear as fossils in early Eocene deposits (Daams, 1999; Daams and De Bruijn, 1995; Uhlig, 2001), suggesting a late Paleocene-early Eocene origin (Hartenberger 1994, 1998), which is concordant with the most recent molecular dating estimate based upon combined markers (Adkins et al., 2003; Huchon et al., 2002). Gnaw marks made by the extinct Eocene glirid Glamys were discovered on fossilized Eocene seeds of a freshwater aquatic floating plant, providing evidence of early glirid behavior (Collinson and Hooker, 2000). Early middle Eocene sediments in Germany have yielded a perfectly preserved Eogliravus wildi (Storch et al., 2000; Storch and Seiffert, 2002) represented by a completely articulated skeleton, soft body outline of pelage over body and tail, gut contents, and baculum. Apparently, E. wildi was agile, arboreal, and fed predominantly on seeds, fruits and buds (Storch et al., 2000; Storch and Seiffert, 2002). Most extant glirid genera were clearly differentiated and exhibited their greatest species diversity by the early to middle Miocene (Daams, 1999; Daams and De Bruijn, 1995; Hartenberger, 1994). The Graphiurinae are an exception; definite examples of Graphiurus are known only as far back as Pliocene (Hendey, 1981; Pocock, 1976), although Denys (1990a), Senut et al. (1992), and Mein et al. (2000a) recorded late Miocene "graphiurines" from South Africa and Namibia. The living Palaearctic genera are but relicts of a rich adaptive radiation of up to 15 genera, and it is hypothesized that Miocene European glirids were ecologically equivalent to certain recent murid assemblages (Hartenberger, 1994).
The origin of glirids, and the evolutionary relationship between glirids and other rodent families are subjects of much morphological and molecular research with contradictory results. Meng (1990) suggested ancestry rooted in reithroparamyids (in Infraorder Sciurida, which also contains Sciuridae; see McKenna and Bell, 1997). Hartenberger (1971, 1994, 1998), Vianey-Liaud† (1994) and Vianey-Liaud and Jaeger (1996) arranged glirids as sciuromorphs rooted in the subfamily Microparamyinae (Ischyromyoidea). Analyses of middle ear anatomy (Lavocat and Parent, 1985) and cephalic arterial supply (Bugge, 1971a, 1985) support a strong phylogenetic affinity between glirids and sciurids. Landry (1999), however, placed dormice in the Phaneraulata of Sciuromorpha, which excludes squirrels but contains dipodoids, muroids, geomyoids, and theridomyids. He regarded the theridomyid pseudosciurines as possibly ancestral to Phaneraulata, with one lineage leading to murids and geomyoids, another to glirids: "It would not be too far off the mark to think of Graphiurus as a surviving pseudosciurine" (Landry, 1999:313). Modern glirids (excluding graphiurines) have been characterized as myomorphous, and several authors included Gliridae within suborder Myomorpha (Chaline and Mein, 1979; McKenna and Bell, 1997; Simpson, 1945; Wahlert, 1978, 1983, 1985; Wahlert et al., 1993; Wood, 1965). Wahlert et al. (1993) placed them within Myomorpha based on derived cranial characters; their phylogenetic reconstruction indicated that the hystricomorphous Graphiurus is the most primitive extant glirid, and the myomorphy exhibited by all other extant glirids is convergent to that of true myomorphs. Vianey-Liaud (1985) employed "pseudomyomorphy" to distinguish the zygomasseteric muscular arrangement exhibited by glirids from murid myomorphy, and this term was endorsed by Maier et al. (2002) to describe the configuration derived from their ontological study of the medial masseter muscle. Landry (1999) agreed that glirids do not exhibit myomorphy, but stated that "pseudosciuromorphy" would be more appropriate for the muscular arrangement, based on his view that the hystricomorphous graphiurines represent the primitive dormouse condition.
The inclusion of glirids in Myomorpha has not been supported by recent morphological and molecular research (Adkins et al., 2001, 2003; Bentz and Montgelard, 1999; Bugge, 1971a, 1985; Corneli, 2002; DeBry and Sagel, 2001; Eizirik et al., 2001; Hartenberger 1971, 1994, 1998; Huchon et al., 1999, 2002; Kramerov, 1999; Kramerov and Vassetzky, 2001; Kramerov et al., 1999; Lavocat and Parent, 1985; Lin et al., 2002; Meng, 1990; Montgelard et al., 2001, 2002; Murphy et al., 2001a; Nedbal et al., 1996; Nikaido et al., 2003; Reyes et al., 1998; Vianey-Liaud 1974, 1985, 1989, 1994; Waddell and Shelley, 2003; Yachontov and Potapova, 1991). Brandtís (1855) subordinal divisions (Sciuromorpha, Myomorpha and Hystricomorpha), which were based on differences in zygomasseteric musculature arrangement, have likewise been contested (Landry, 1999; Luckett and Hartenberger, 1985b; Nedbal et al., 1996). Most authors now associate glirids with sciurids (or with Hystricognathi, when sciurids were not included in analyses); they agree with Wahlert et al. (1993) that the myomorphous condition exhibited by most modern glirids is convergent with muroids, though most advocate glirid myomorphy as being derived from a protrogomorphous ancestor. Moreover, recent molecular analyses support the grouping of sciurids and aplodontids (Suborder Sciuromorpha of McKenna and Bell, 1997) with glirids, and suggest that Gliridae is the sister clade to that containing Sciuridae and Aplodontidae (Adkins et al., 2001, 2003; Huchon et al., 1999, 2002; Montgelard et al., 2002). If protrogomorphy is the primitive state for glirids, the hystricomorphy exhibited by graphiurines was either 1) derived from the primitive protrogomorphous morphology, thus representing a lineage independent of all other dormice, which would be concordant with several morphological studies (e.g., Yachontov and Potapova, 1991; Wahlert et al., 1993); or 2) derived from the myomorphous state (Vianey-Liaudís, 1985, "pseudomyomorphy") shared by other modern glirids, which would be consistent with other morphological studies (e.g., Daams and De Bruijn, 1995; Koenigswald, 1993, 1995).
Vianey-Liaud and Jaeger (1996) proposed Gliridae to be paraphyletic, hypothesizing that graphiurines (which they advocated placing in a separate family, Graphiuridae) are most closely related to anomalurids. They further suggested that anomalurids and graphiurines should possibly be placed in the same family, based on their view that both groups are descended from zegdoumyids. All other recently published molecular and morphological studies support the monophyly of Gliridae (Catzeflis et al., 1995; Daams and de Bruijn, 1995; Debry and Sagel, 2001; Hanni et al., 1995; Hartenberger, 1994, 1998; Huchon et al., 1999, 2002; Meng, 1990; Montgelard et al., 2001, 2002, 2003; Robinson et al., 1997; Storch 1995b; Suzuki et al., 1997; Wahlert et al., 1993), and results of molecular analyses by Bentz and Montgelard (1999) and Montgelard et al. (2001, 2002) explicitly refute the hypothesis of paraphyly and phylogenetic alliance with anomalurids.
Wahlert et al. (1993) incorporated dental characters plus forty-three osteological traits in a phylogenetic analysis of extant glirid genera. Except for the inclusion of Muscardinus in Leithiinae (Montgelard et al., 2003) instead of Glirinae, Wahlert et al.ís classification is followed here because it reflects the most comprehensive phylogenetic analysis of glirids thus far. Several recent reviews and analyses address intrafamilial relationships using a variety of characters: molecular data (Bentz and Montgelard, 1999; Filippucci and Kotsakis, 1995; Montgelard et al., 2003; Suzuki et al. 1997); karyotypic information (Zima et al., 1995); dental morphology (Daams and De Bruijn, 1995; Pavlinov, 2001b); incisor enamel microstructure (Koenigswald, 1993, 1995); cranial and dental morphology (Vianey-Liaud and Jaeger, 1996); cranial, dental and genital morphology (Storch, 1995b); cranial, masticatory and tongue structure (Yachontov and Potapova, 1991). Each study has provided valuable insight, data and hypotheses regarding the relationships among dormice. Some of their conclusions support the hypotheses of Wahlert et al. (1993), others are contradictory. It is not possible to follow any one of these alternate classifications here because usually the methodology used to deduce relationships among glirid genera was not given. Dendrograms depicting hypothesized relationships were provided, as were descriptions of characters, but essential information regarding character states and polarities, numbers and origins of specimens examined, and methodology was either absent or inconsistent. In the few studies that clearly documented methodology and character states, the results were either inconclusive (Bentz and Montgelard, 1999; Zima et al., 1995) or sampled too few taxa to provide a comprehensive hypothesis of intrafamilial relationships (Filippucci and Kotsakis, 1995; Suzuki et al., 1997; Zima et al., 1995). The phylogenetic analyses of DNA nuclear fragments and mitochondrial gene sequences by Montgelard et al. (2003:1953) is an exception: ". . . except for the position of Muscardinus . . ., the identification of three major glirid clades (Graphiurus, Muscardinus + Leithiinae and Glis + Glirulus) on molecular grounds confirms and extends the classification proposed by Wahlert et al. (1993) on the basis of morphological data."
Rossolimo et al. (2001) provided a comprehensive review of recent and fossil glirids, including descriptions and illustrations of cranial characters, zygomasseteric myology, internal bullar morphology and review of phylogeny. Each detailed species account contains illustrations of live animals, measurements, karyological data, ecological information, vocalization data, ectoparasite records and a distribution map. Review and comparison of vocalization data among glirid genera reported by Hutterer and Peters (2001) and Nowakowski and Rachwald (2000). The Dormouse Hollow (www.glirarium.de/dormouse), edited by Werner Haberl, provides a variety of information about dormice, including past and current research by glirid specialists. For synonyms see McKenna and Bell (1997).