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A NEW SPECIES OF PETROMUS (RODENTIA, HYSTRICOGNATHA, PETROMURIDAE) FROM THE EARLY PLIOCENE OF SOUTH AFRICA AND ITS PALEOENVIRONMENTAL IMPLICATIONS

The family Petromuridae Tullberg, 1899, is represented by the single genus, Petromus A. Smith, 1831, and only one recent species is currently recognized, Petromus typicus A. Smith, 1831. This taxon is restricted to the southwest arid zone of Africa (Scott, 1990), from the extreme south of Angola to Namaqualand (western part of South Africa) passing through Namibia (Fig. 1). It lives in arid or semi-arid areas and “marginally in the Southern Savanna biotic zone” (De Graaff, 1981). Petromus is diurnal and restricted to rocky areas where it lives in crevices (De Graaff, 1981; Skinner and Smithers, 1990). It feeds mainly on grass, but its diet also includes leaves, stems, and flowers when available (Scott, 1990). De Graaff (1981) indicated that the Petromuridae should be revised because of the impressive number of subspecies recorded in a small area. Musser and Carleton (1993) suggested that most of the sub-species are invalid. Nedbal et al. (1994) and Huchon and Douzery (2001) confirmed by molecular analysis a close relationship between the Petromuridae and Thryonomyidae Pocock, 1922. These authors agree with prior studies (e.g., Lavocat, 1973; Luckett and Hartenberger, 1985) in placing these two families in a monophyletic superfamily Thryonomyoidea. The Petromuridae has a poorly known fossil record. Petromus was recorded in the “post-Miocene” of the Otavi mountains and Kaokoland, northern Namibia (Pickford et al., 1994). Prior to the present study, the only described fossil species of the genus was Petromus minor Broom, 1939, found at Taung (Fig. 1) in the late Pliocene (Broom, 1939; De Graaff, 1960; Cooke, 1963). The collections of the University of California studied by Cooke in 1990 did not reveal additional material. The holotype and only specimen is an incomplete cranium with one toothrow (Fig. 2, measurements in Table 1). The teeth greatly resemble those of the recent species P. typicus, except for the slightly more transverse orientation of the crests. The diagnosis of P. minor is accompanied by an imprecise drawing. Petromus antiquus sp. nov. is based on material found at Waypoint 160. This locality is one of the many sites found in the Bolt’s Farm area (Fig. 1), three kilometers southwest of Sterkfontein in Gauteng Province, South Africa. Waypoint 160 has already yielded a unique microfauna in which most of the species are new (Sénégas and Avery, 1998; Sénégas and Michaux, 2000); other taxa still under study. The importance of this site is considerable because of its early Pliocene age (Sénégas and Avery, 1998); it is the oldest locality in the Gauteng Province. Abbreviations—M, upper molar; m, lower molar; P, upper premolar; p, lower premolar; Md, mandible; Mx, maxillae. The classification follows McKenna and Bell (1997). All the specimens are housed in the Department of Palaeontology of the Transvaal Museum, Pretoria, South Africa.