Otomyinae Thomas 1896

Otomyinae Thomas 1896, Proc. Zool. Soc. Lond., 1896: 1017.

Synonyms: Otomyini Tullberg 1899; Otomyidae Roberts 1951 .

Genera: 3 genera with 23 species:

Genus Myotomys Thomas 1918 (2 species)

Genus Otomys F. Cuvier 1824 (19 species)

Genus Parotomys Thomas 1918 (2 species)

Discussion: Morphologically, a strongly circumscribed group of species indigenous to Subsaharan Africa. Early on ranked as a subfamily of Muridae, whether defined sensu lato (Thomas, 1896; Ellerman, 1941; Roberts, 1951) or sensu stricto (Tullberg, 1899; Miller and Gidley, 1918; Simpson, 1945; Reig, 1981); or even a separate family (Roberts, 1951); and later considered a subfamily of Cricetidae (Misonne, 1974) or Nesomyidae (Chaline et al., 1977; Lavocat, 1978). Paleontological evidence and anatomical considerations unequivocally affirm their phyletic origin from African murines, especially arvicanthine-like forms (Pocock, 1976; Carleton and Musser, 1984; Bernard et al., 1991; Breed, 1995 d; Sénégas, 2001). Similarly, evolutionary affinities inferred from DNA-DNA hybridization (Chevret et al., 1993 b), immunological assays (Contrafatto et al., 1994; Watts and Baverstock, 1995 a), and mitochondrial and nuclear DNA sequences (Ducroz et al., 2001; Jansa and Weksler, 2004; Michaux and Catzeflis, 2000; Michaux et al., 2001 b) uniformly represent Otomys as a "murine," either as sister group to Arvicanthis Oenomys (Chevret et al., 1993 b) or to arvicanthines in the broad sense (Ducroz et al., 2001). Molecular clock estimates place the split from arvicanthine murids about 7-8.5 million years ago (Chevret et al., 1993 b; Ducroz et al., 2001), a time frame in broad agreement with fossil data insofar as known (Sénégas, 2001).

The above phylogenetic perspective indicates that otomyines should be merged under Murinae, probably as a tribe, as specifically urged by some (Ducroz et al., 2001; Jansa and Weksler, 2004; Michaux et al., 2001 a; Watts and Baverstock, 1995 a). Certain of these studies (Ducroz et al., 2001; Watts and Baverstock, 1995 a), moreover, convey a deep, monophyletic separation of the African radiation (including otomyines) within Murinae as currently constituted. The larger nomenclatural issue involves the stability of this clade and its possible formal recognition, in which case Otomyinae Thomas, 1897, has priority as the applicable family-group name. The rank accorded and genera allocated to otomyines thus seem premature until relationships among African, Asian, and Indo-Australian murines are more confidently rendered; many of the latter are already type genera for variously recognized family-group taxa (see Murinae account). In lieu of this broader picture, we acknowledge otomyines and their distinctive combination of traits, unobserved elsewhere within Murinae, as a subfamily within Muridae .

Aspects of morphology surveyed and discussed by Bernard et al. (1990, 1991), Bohmann (1952), Breed (1995 d), Carleton and Musser (1984), Jackson and Spinks (1998), Perrin and Curtis (1980), Taylor and Kumirai (2001), Thomas (1918 b), and Tullberg (1899). Chromosomal information reviewed by Meester et al. (1992) and Taylor (2000 b). For extensive paleontological coverage, including the annectant fossil genus Euryotomys (Mio-Pliocene, South Africa) and probable southern African origin of the subfamily, see Avery (1998), Chevret et al. (1993 b), Denys (1989 a), Denys et al. (1987), Pocock (1976, 1987), Sénégas (2001), and Sénégas and Avery (1998). Meester et al. (1986) consolidated nomenclatural information and identified provisional subspecies arrangements for taxa in the Southern African Subregion; taxonomy of East African forms too poorly understood to justify formal infraspecific divisions. Habitat preferences and conservation implications considered by Mugo et al. (1995) for species in South Africa.

Vlei and whistling rats have been variously classified into a single genus (Bohmann, 1952), commonly as the two genera Otomys and Parotomys (Ellerman, 1941; Ellerman et al., 1953; Misonne, 1974; De Graaff, 1981; Smithers, 1983; Meester et al., 1986; Corbet and Hill, 1991; Musser and Carleton, 1993), or as many as three (Thomas, 1918 b; Pocock, 1976) or five (Roberts, 1951). The diverse generic arrangements principally reflect the emphasis on dentition versus bullar development as the pivotal trait of kinship. Recent multispecific surveys and phylogenetic studies of allozymes (Taylor et al., 1989), chromosomes (Meester et al., 1992), immunological data (Contrafatto et al., 1994), sperm structure (Bernard et al., 1991), and mtDNA (Ducroz et al., 2001) reveal that Otomys, as its specific contents are usually denoted, is polyphyletic; in particular, the species sloggetti and-or unisulcatus demonstrate close kinship with members of Parotomys . Several morphological traits also support this nearer relationship: absence of lower incisor sulci (present in all Otomys); weak sulcation of the upper incisors (deeply creased in Otomys); fewer M3 laminae (4-5 versus 6 or more in Otomys); gradually tapered nasals (distal nasals abruptly expanded in Otomys); vascular foramen basal to zygomatic plate small (large in Otomys); zygomatic plate narrow, not reaching the premaxillary-maxillary suture (plate broader, overlapping suture in Otomys); ventrolateral maxillary not extended anteriorly (ventrolateral projection, bearing insertion scar of the superficial masseter, conspicuous in Otomys). Such plesiomorphic features suggest the earlier cladistic origin of sloggetti unisulcatus and Parotomys relative to the appearance and radiation of Otomys . Still, sloggetti and unisulcatus lack the hypertrophied ectotympanic bullae that characterize Parotomys, as well as other traits noted by Thomas (1918 b). We provisionally return to the classification of Thomas (1918 b), who provided useable diagnoses of his three genera ( Myotomys, Otomys, and Parotomys) and whose arrangement is so far consistent with the emerging phylogenetic perspective, admitting its very preliminary and incomplete nature.