Molecular and morphological evidence for a P leistocene radiation of laminate‐toothed rats ( Otomys : R odentia) across a volcanic archipelago in equatorial A frica

W est A frican M ountains of the C ameroon V olcanic L ine harbour two montane‐endemic species of laminated‐toothed rats ( Otomys ), which represent the most westerly occurrence of the genus. We explore here through mtDNA sequencing and cranial morphometrics the taxonomic status and phylogenetic relationships of O. burtoni ( M t C ameroon) and O. occidentalis ( M ts O ku and G otel). We conclude that both species are valid and can be discriminated by molecular data, as well as quantitative and qualitative cranial characters. From molecular data, O. occidentalis and O. burtoni are closest neighbours ( p ‐distance = 7.5–8.5%) and weakly associated sister species (suggesting a single West A frican radiation) and both are sister clades to a well supported clade of central, East and northeast A frican members of the O. typus s.l. and O. tropicalis s.l. species complexes from mountain ranges comprising the East A frican ‘ M ontane C ircle’ and E thiopian H ighlands. Re‐evaluation of the evolutionary origins of the allopatric Otomys populations in e quatorial A frica is undertaken in light of fossil evidence of a southern A frican origin of the genus. We can conclude that Otomys reached the C ameroon V olcanic L ine via corridors of temperate grasslands during the L ate P liocene. Our data support the hypothesis that, following major peripatric speciation events at around 2.3 to 2.03 Ma (from East A frica into West and North A frica respectively), further speciation occurred across neighbouring mountain ranges in West, Central‐East and North‐East A frica. Estimated molecular dates of speciation events in Otomys reveal close congruence with well‐constrained geochronological estimates, pertinently the uplift of the A lbertine R ift in the E arly P leistocene. These regional analyses reveal how peripatric speciation events established narrow‐range endemics of Otomys on principal stratovolcanoes across the E ast A frican plateau and C ameroon. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society , 2014, 113 , 320–344.