Detailed diagnosis, general characteristics, and natural history provided by Carleton and Musser (1984). Since Blyth (1859) described Platacanthomys as a genus of Gliridae, Platacanthomys and Typhlomys have been regarded: as a subfamily of dormice (Ellerman, 1940, 1961; Ognev, 1947; Thomas, 1896); a family related to Gliridae (Simpson, 1945); a family allied with Cricetidae (G. M. Allen, 1940; Miller and Gidley, 1918; Pavlinov et al., 1995a; Qiu, 1989); a subfamily or tribe within Cricetidae (Chaline et al., 1977; Engesser, 1972; Fahlbusch, 1966; Mein and Fredudenthal, 1971; Reig, 1980; Schaub and Zapfe, 1953); allied to "the Murine family of Rodents" (Peters, 1865); or as a subfamily of a broadly defined Muridae (Alston, 1876; Carleton and Musser, 1984; Musser and Carleton, 1993). Separation from dormice and alliance with Muroidea have been supported by paleontologists, our own examinations, and those of others (Fejfar, 1999b; Stehlin and Schaub, 1951; Vorontsov, 1979). Morphological differences between Platacanthomys and Typhlomys are pronounced, to an extent that Ognev (1947) arranged each in its own glirid subfamily, a treatment that Vorontsov (1979) thought extreme and unnecessary.
While molar similarities between platacanthomyids and dormice are superficial, those between platacanthomyids and the Madagascan nesomyine Gymnuromys are actually closer (Ellerman, 1940; Wood, 1955). Stehlin and Schaub (1951) also demonstrated that occlusal patterns in Platacanthomys are not homologous to those of dormice and can be derived from a "cricetid plan." In naming the Miocene Neocometes, Schaub and Zapfe (1953) arranged it, along with Platacanthomys and Typhlomys, as a tribe within Cricetinae. Platacanthomyids have three cheekteeth (all molars) in each quadrant of the jaw (four in dormice, premolar and three molars), small muroid-type ectotympanic bullae without septa (bullae globular with conspicuous transbullar septa in dormice), and the dentary is neither inflected lingually nor perforated (traits characteristic of dormice).
Extinct Pleistocene and Miocene species of Platacanthomys and Typhlomys have now been described from China (Fejfar, 1999b; Ni and Qiu, 2002; see generic accounts), and a "platacanthomyid" has been identified from early middle Miocene (17 million year ago) strata in the Siwaliks of N Pakistan (Flynn, 2003). Apparently, platacanthomyids originated in Asia and reached Europe in the Miocene, as far as Spain (de Bruijn and Moltzer, 1974). Platacanthomys and Typhlomys, although characterized by many specialized features, are relicts of a clade recognizable as platacanthomyid by the early Miocene. Because extinct forms are contemporaneous with early to late Miocene cricetids and their dentitions are so strikingly unlike the cricetid genera, platacanthomyids likely originated from some Eocene or Oligocene, probably Asian, muroid stock (Carleton and Musser, 1984). The platacanthomyid molar patterns and their relative sizes (upper and lower second and third molars large relative to first) could have evolved from a morphology resembling that in Eucricetodon, which flourished from early Eocene to early Miocene in Asia and early Oligocene to early Miocene in Europe (McKenna and Bell, 1997). Species of Eucricetodon were replaced by Miocene cricetids unrelated to Eucricetodon and its allies (Hugueney, 1999) or to platacanthomyids.
Closest relatives of Platacanthomys and Typhlomys are Neocometes brunonis and N. similis from early to late Miocene of Europe (de Bruijn and Moltzer, 1974; Fahlbusch, 1966; Mein and Freudenthal, 1971; Schaub and Zapfe, 1953; Ziegler, 1995), recorded as far northeast as Poland (Kowalski, 1993); Neocometes sp. from early Miocene in S China (Qiu and Li, 2003); and N. orientalis from early Miocene in N Thailand (Mein et al., 1990; Mein and Ginsburg, 1997), which is the oldest and regarded as the most primitive of the three species (see review by Fejfar, 1999b). Schaub and Zapfe (1953) considered Neocometes to be morphologically close to Typhlomys, a relationship endorsed by Fejfar (1999b), who noted that Platacanthomys has more derived dental traits and represents a separate evolutionary branch.
Current common names (e.g., Wilson and Cole, 2000) are Malabar spiny dormouse (Platacanthomys) and pygmy dormouse (Typhlomys). Either "tree mouse" or incorporation of the genus is preferred; both arrangements avoid perpetuating the incorrect phylogenetic alliance implied by the usual vernaculars.