Michael D. Carleton

Review of the Hylomyscus denniae complex (Rodentia: Muridae) in Tanzania, with a description of a new species

ABSTRACT Based on morphological and morphometric comparisons, a new species of Hylomyscus, H. arcimontensis (Muridae: Murinae), is identified from Mount Rungwe and the Eastern Arc Mountains of central and eastern Tanzania. The new species is confined to wet montane forests of these mountains and represents another vertebrate endemic to the Tanganyika-Nyasa Montane Forest biotic region (sensu Moreau 1966). It is most closely related to H. anselli, a form described from mountains in northern Zambia as a subspecies of H. denniae and here elevated to species rank. Morphological evidence supports the view that the nominal species H. denniae is a composite of several species whose interrelationships and differentiation patterns indicate two species complexes: the H. denniae group centered in Central East African mountains (Burundi, Kenya, Rwanda, Uganda, Zaire) and the H. anselli group distributed across more southern mountains (Angola, Malawi, Tanzania, Zambia).

Review of the Hylomyscus denniae group (Rodentia: Muridae) in eastern Africa, with comments on the generic allocation of Epimys endorobae Heller

ABSTRACT The status and distribution of eastern African populations currently assigned to Hylomyscus denniae are reviewed based on morphological and morphometric comparisons. Three species are considered valid, each confined largely to wet montane forest above 2000 meters: H. denniae (Thomas, 1906) proper from the Ruwenzori Mountains in the northern Albertine Rift (west-central Uganda and contiguous D. R. Congo); H. vulcanorum Lönnberg & Gyldenstolpe, 1925 from mountains in the central Albertine Rift (southwestern Uganda, easternmost D. R. Congo, Rwanda, and Burundi); and H. endorobae (Heller, 1910) from mountains bounding the Gregory Rift Valley (west-central Kenya). Although endorobae has been interpreted as a small form of Praomys, additional data are presented that reinforce its membership within Hylomyscus and that clarify the status of Hylomyscus and Praomys as distinct genus-group taxa. The 12 species of Hylomyscus now currently recognized are provisionally arranged in six species groups (H. aeta, H. alleni, H. anselli, H. baeri, H. denniae, H. parvus) based on 8 qualitatitive characters. Biogeography of the three species of the H. denniae group is discussed in the context of broad distributional patterns and area relationships evident among other terrestrial small mammals also confined to the Afromontane biotic region in eastern Africa.

Chapter 5. A New Species of Reithrodontomys, Subgenus Aporodon (Cricetidae: Neotominae), from the Highlands of Costa Rica, with Comments on Costa Rican and Panamanian Reithrodontomys

Abstract A new species of the rodent genus Reithrodontomys (Cricetidae: Neotominae) is described from Cerro Asunción in the western Cordillera de Talamanca, Costa Rica. The long tail, elongate rostrum, bulbous braincase, and complex molars of the new species associate it with members of the subgenus Aporodon, tenuirostris species group. In its diminutive size and aspects of cranial shape, the new species (Reithrodontomys musseri, sp. nov.) most closely resembles R. microdon, a form known from highlands in Guatemala and Chiapas, Mexico. In the course of differentially diagnosing the new species, we necessarily reviewed the Costa Rican and Panamanian subspecies of R. mexicanus based on morphological comparisons, study of paratypes and vouchers used in recent molecular studies, and morphometric analyses. We recognize Reithrodontomys cherrii (Allen, 1891) and R. garichensis Enders and Pearson, 1940, as valid species, and allocate R. mexicanus potrerograndei Goodwin, 1945, as a subjective synonym of R. brevirostris Goodwin, 1943. Critical review of museum specimens collected subsequent to Hoopers (1952) revision is needed and would do much to improve understanding of Reithrodontomys taxonomy and distribution in Middle America.

Chapter 3. Review of the Oryzomys couesi Complex (Rodentia: Cricetidae: Sigmodontinae) in Western Mexico

Abstract The status and distribution of eight species-group taxa of the Oryzomys couesi group (Rodentia: Cricetidae: Sigmodontinae) described from western Mexico are evaluated based on morphological and morphometric comparisons. Four of these are recognized as valid species within the region: Oryzomys albiventer Merriam, 1901 (including molestus Elliot, 1903), from inland plateau of the Mesa de Anáhuac; O. couesi mexicanus J.A. Allen, 1897 (including bulleri J.A. Allen, 1897; lambi Burt, 1934; rufus Merriam, 1901), from Pacific coastal plain, contiguous lower mountain slopes, and interior valleys along the Ríos Tepalcatepec–Balsas; O. nelsoni Merriam, 1898, from Isla María Madre; and O. peninsulae Thomas, 1897, from the southern tip of the Baja California Peninsula. Three other taxa named from uplands in interior Mexico—aztecus Merriam, 1901; crinitus Merriam; 1901; and regillus Goldman, 1915—are provisionally retained within O. couesi, but further study of their specific stature and relationships is required. The recommended taxonomic changes within western Mexico serve to discuss directions for future revisionary research that will refine the definition and distribution of O. couesi sensu stricto in Middle America.

Chapter 1. They Sort Out Like Nuts and Bolts: A Scientific Biography of Guy G. Musser

‘‘They sort out like nuts and bolts,’’ or similar wording, was an assertion that regularly arose in my conversations or correspondence with Guy over the past 40 years. The ‘‘they’’ in this statement are species of IndoAustralian rodents (Muroidea: Muridae: Murinae), a diverse and taxonomically complex Old World group that would dominate his research contributions and secure his professional reputation as one of the foremost systematic mammalogists of his generation. The statement carried an implicit comparative context: it referenced Guy’s formative experiences with a comparably complex group of New World rodents, deer mice of the genus Peromyscus (Muroidea: Cricetidae: Neotominae), research that comprised some of his earliest taxonomic works. The subtle features consulted to distinguish Peromyscus species served to sharpen his eye for specific discrimination whenever applied to other muroid genera investigated thereafter, particularly Rattus and kin.