Phylogenetic analyses of mitochondrial and nuclear gene sequences support the monophyly of Gerbillinae and Murinae (Adkins et al., 2001; Montgelard et al., 2002; Robinson et al., 1997); Deomyinae, Gerbillinae, and Murinae (Catzeflis et al., 1995; Conroy and Cook, 1999; Dubois et al., 1999; Hänni et al., 1995; Martin et al., 2000); and those three subfamilies plus Otomyinae (Jansa and Weksler, 2004; Michaux and Catzeflis, 2000; Michaux et al., 2001b). Until analyses of molecular data recovered a monophyletic clade consisting of Acomys, Lophuromys, Uranomys, and Deomys (Deomyinae), the first three genera had been listed in classifications and checklists under Murinae. They share many of the diagnostic cranial traits associated with murines and the defining "upper first molars with three cusps in the anterior two transverse chevrons" and positions of the two lingual cusps relative to the adjacent central cusps (Carleton and Musser, 1984; Flynn et al., 1985:605). Deomys was either viewed as the sole member of Deomyinae or an unusual dendromurine (see Deomys account). Gerbils have been treated as a separate family within Muroidea or subfamily within Cricetidae (separated from Muridae) or more encompassing Muridae (see Gerbillinae introduction). Although strongly differentiated in external and cranial characters among muroids, most gerbil species lack longitudinal enamel crests on their molars, as found in cricetids, and resemble murines in this derived trait, which has been the primary basis for postulating a sister-group relationship between Gerbillinae and Murinae (Flynn et al., 1985; Tong and Jaeger, 1993).
Despite past treatments of otomyines as an independent family (Roberts, 1951), subfamily of Nesomyidae (Chaline et al., 1977; Lavocat, 1978) or Cricetidae (Misonne, 1974), or in an inclusive Muridae generally comparable to Muroidea (Carleton and Musser, 1984; Ellerman, 1941; Thomas, 1896), morphological information from fossil and living samples, along with sequences from mitochondrial and nuclear genes, unequivocally link Vlei and Whistling Rats with African murines (see Otomyinae introduction). Including Otomyinae within a restricted Muridae (separate from Cricetidae) was already formulated by Tullberg (1899), Miller and Gidley (1918), and Simpson (1945). Cranial, dental, and mandibular conformation of otomyines lacks derived traits that link them with any other African clade, living or fossil, and resembles the cranial configuration of arvicanthine genera (especially Arvicanthis, Pelomys, and Mylomys). Furthermore, there is an impression that enlarged M3s (with four to 10 laminae) and m1s (four to seven laminae), diagnostic of otomyines, are not found elsewhere among murids and are only seen in nonmurid groups (Misonne, 1969). The species of late Miocene Microtia from the Gargano fissure fillings in southern Italy are typical European Neogene murines, possibly derived from Stephanomys or Apodemus, with enlarged M3s and m1s accommodating four to seven transverse, tubercular and chevron-like laminations (Freudenthal, 1976; Freudenthal and Suárez, 1999; Jaeger and Hartenberger, 1989; Millien and Jaeger, 2001; Millien-Parra, 2000b; Zafonte and Masini, 1992). The laminae of otomyines are flat and lack indication of the murine triserial pattern and cuspidation (except in early fossils) but the proliferation of laminae in Microtia and otomyines suggests a deep shared genetic heritage.
We isolate the African Leimacomys in its own subfamily to highlight the enigmatic nature of its mosaic character pattern and uncertain phylogenetic affinities. Usually associated with dendromurines (see Leimacomyinae introduction), its cranial configuration is unlike any genus in that group and instead resembles murines, gerbils, and deomyines such as Lophuromys. Molar occlusal patterns were thought to match those in the dendromurine Steatomys, but in many ways are more similar to gerbillines (Denys et al., 1995) or extinct myocricetodontines (C. Denys, in litt., 2001). While nesting Leimacomyinae within Muridae seems to reflect morphology, its status as an independent clade, or alternatively as a member of either Deomyinae or Gerbillinae, will require testing with a broader survey of African genera in Muridae and Nesomyidae in which the focus is on morphological traits other than just dentition, and the incorporation of DNA gene sequences.
Evolutionary origin of the Muridae as constituted here may be traced back through extinct myocricetodontines (early Miocene and late Miocene-early Pliocene in Arabian Peninsula, early to late Miocene in Pakistan, middle Miocene of China, middle to late Miocene in North and East Africa, early to middle Miocene of Turkey, and late Miocene-early Pliocene in Spain; Qiu, 2001; Wessels, 1996) to early Miocene cricetids such as Spanocricetodon in Pakistan and and the morphologically similar Notocricetodon of Africa (de Bruijn et al., 1996). Tong and Jaeger (1993) speculated that myocricetodontines are paraphyletic, producing both gerbils and murines, which may be a sister-group to African dendromurines and cricetomyines; they estimated divergence of gerbillines-murines from dendromurines-cricetomyines at 18 million years before present. Such a relationship is reflected in the phylogenetic analyses of nuclear IRBP gene sequences by Jansa and Weksler (2004) in which those deomyines, gerbillines, and otomyines sampled (here = Muridae) form a major sister-group to exemplars of nesomyines, dendromurines, cricetomyines, mystromyines, and petromyscines (here = Nesomyidae).