Otomys cheesmani Taylor et al. 2011

Mizerovská, Daniela, Martynov, Aleksey A., Mikula, Ondřej, Bryjová, Anna, Meheretu, Yonas, Lavrenchenko, Leonid A. & Bryja, Josef, 2023, Genomic diversity, evolutionary history, and species limits of the endemic Ethiopian laminate-toothed rats (genus Otomys, Rodentia: Muridae), Zoological Journal of the Linnean Society 199 (4), pp. 1059-1077 : 1071-1072

Otomys cheesmani Taylor et al. 2011

Cheesman’s Vlei Rat

Holotype: BMNH 1937.2.24.84; adult male, dry skin and skull, collector’s number 7400; collected by R. E. Cheesman, 20 October 1937.

Type locality: Ethiopia, vicinity of Dangila , 66 km south of Lake Tana, 2100 m a.s.l.. The type material was collected in an intrazonal wetland habitat. However, it is now changed into agricultural landscape ( Kostin et al. 2020) .

Taxonomic notes: The largest Ethiopian Otomys species with robust skull with broad nasal bones, thickened zygomatic arches, and relatively narrow interorbital region (Supporting Information, S4). The upper third molar has eight or nine complete laminae (see more details in Taylor et al. 2011). Kostin et al. (2020) reported a recent sampling in the region, from where the species was described and hypothesized that it is extinct because of intensive destruction of its original habitat. We recently (2018) sampled large Otomys in wet grasslands in middle elevation (2640 m a.s.l.) close to Kombolcha. They are distinct genetically from the remaining species in the SIMIENSIS group and we hypothesized that they might represent O. cheesmani (we called them here O. cf. cheesmani ). Very similar Cytb was identified also in the material collected by K. Welegerima in Emba Sadege (3450 m a.s.l.) and Awo Forests (1980 m a.s.l.) in Tigray. However, the only adult skull available for morphometric analysis is not similar to the type series of O. cheesmani ( Fig. 7 ; Supporting Information, S4). Unfortunately, the skulls of the material from Tigray are not currently available, and the second specimen from Kombolcha ( ETH 1755) was a juvenile with a broken skull. It is, therefore, possible that O. cf. cheesmani represents another species in the SIMIENSIS group. Future research should compare this taxon with the holotype of O. degeni from Gombitchu (2450 m a.s.l.) in central Ethiopia, not far from Addis Ababa. The skull morphology of the holotype of O. degeni was clearly distinct from all other Ethiopian Otomys , but it was provisionally included in the synonymy with O. typus ( Taylor et al. 2011) , which is most likely incorrect. Based on the morphology, a population from Jimma (1750 m a.s.l.), shown in Taylor et al. (2011: fig. 6), could also belong to this taxon. It must be also noted that our localities of O. cf. cheesmani are separated from those of O. cheesmani by the Blue Nile Valley, which is an important biogeographical barrier for many taxa (e.g. Lophuromys , Desmomys , Dendromus , Stenocephalemys , and Tachyoryctes ; see Kostin et al. 2020). To solve this taxonomic question, it would be necessary to collect and morphologically analyse more specimens of O. cf. cheesmani (including those from Jimma; Taylor et al. 2011), to analyse their karyotypes and to obtain genetic data from historical specimens in the type series of O. cheesmani and from the holotype of O. degeni .

Distribution: The species (or more likely two species) is restricted to the north-western part of the Ethiopian Highlands. The type material of O. cheesmani was collected at two localities in north-western Ethiopia at the elevation 2100–2500 m a.s.l. Elevational distribution of O. cf. cheesmani is broader: 1982 m a.s.l. (Awo forest), 2641 m a.s.l. (Atari Mesk Valley close to Kombolcha), and 3450 m a.s.l. (Emba Sadege forest).

Figures

Figure 7. Ordination of skull shapes of three Otomys species of the SIMIENSIS group in the space of the first two principal components. Type specimens are shown by stars.