METAPHIOMYS (RODENTIA: PHIOMYIDAE) FROM THE PALEOGENE OF SOUTHWESTERN TANZANIA

[Extract] The evolutionary history of the living African rodent families is a topic of considerable debate, yet it is generally agreed that the modern cane rats (Thryonomys Fitzinger, 1867) and dassie rats (Petromus Smith, 1831) have an evolutionary history within the infraorder Phiomorpha (e.g., Wood, 1968). Phiomorphs possess hystricognathous mandibular morphology, multiserial incisor enamel, and hystricomorphous attachment of the masseteric musculature (e.g., Lavocat, 1978; Holroyd, 1994). In his initial work on the group, Wood (1968) placed all phiomorph taxa into a single family, and named a handful of morphologically diverse species based mainly on size. Lavocat (1978) later revised the taxonomy of the group, raising many of the differences among species to the family level. More recently, Holroyd (1994) observed that these contrasting views likely stemmed from the fact that Wood's phiomorph work emphasized the overall similarity of Paleogene specimens from the Fayum of Egypt, whereas Lavocat endeavored to explain the diverse Miocene rodent faunas from East Africa, envisioning that each of the Miocene forms had an ancestor among the Paleogene taxa. In this paper we adopt Holroyd's (1994) revised version of family-level relationships among the phiomorphs. A variety of well-preserved specimens pertaining to phiomorph evolutionary history have been described from the Paleogene of northern Africa and Oman (Osborn, 1908; Wood, 1968; Jaeger et al., 1985; Fejfar, 1987; Holroyd, 1994) and Asia (e.g., Flynn et al., 1986; Jaeger, 1988; Marivaux et al., 2002; Marivaux and Welcomme, 2003). However, Paleogene terrestrial deposits in sub- Saharan Africa are extremely rare, hence this constitutes the earliest phiomorph record from East Africa. Here we announce a new microsite in the Mbeya Region of southwestern Tanzania, preserving Metaphiomys Osborn, 1908, a rodent taxon previously described exclusively from the early Oligocene of Egypt, Libya, and Oman (Wood, 1968; Fejfar, 1987; Thomas et al., 1989). Not only does this represent a significant geographic extension of the taxon, it also constitutes the first rodent material described from the Paleogene of East Africa.