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We describe and name three new species of Musseromys from the mountains of northern Luzon based on morphological and DNA sequence data. Previously, Musseromys was known only from one species from the lowlands of central Luzon. These are the smallest-known members of the cloud rat clade of endemic Philippine murids, weighing only 15–22 g, an order of magnitude smaller than the previously smallest known members of the clade (Carpomys spp.), and more than two orders of magnitude smaller than the largest members (Phloeomys spp.). These discoveries raise the number of native murids documented on Luzon to 43, 93% of which are endemic, and 88% of which are members of two endemic Philippine clades. Musseromys is inferred to have originated in montane habitats, probably in the Central Cordillera of northern Luzon, with movement to two other areas on Luzon, one in montane habitat and one in lowland habitat, associated with the speciation process.

Shrew mice of the genus Archboldomys are poorly known members of an endemic clade of vermivorous/insectivorous murid rodents confined to Luzon Island, Philippines. Three species of these small, ground-living, diurnal mice were previously known, all from a handful of specimens from a few localities. The pattern of morphological and genetic differentiation among additional specimens of shrew mice from our recent field surveys in the Central Cordillera and Sierra Madre mountains of Luzon document the presence of two distinct species groups within Archboldomys as previously defined, as well as three new species. Gene-sequence data from the mitochondrial cytochrome b and nuclear IRBP genes confirm the existence of six distinct species, but also show that Archboldomys, as previously defined, is composed of two clades that are not sister taxa. Reevaluation of the presumed morphological synapomorphies among these shrew mice, together with analyses of karyological and gene-sequence data, support the follo...