Four new species of the Hylomyscus anselli group (Mammalia: Rodentia: Muridae) from the Democratic Republic of Congo and Tanzania

As in many other small mammal groups from the Afrotropics, the number of species recognized within the genus Hylomyscus has increased considerably over the past dozen years. The last comprehensive review (2005) of the genus recognized eight species. Since that time, nine additional species have been elevated from synonymy (n = 4) or described as new (n = 5). Here we describe four additional new species supported by morphological and molecular evidence, all collected by the late William Stanley. Two of the new taxa are sympatric and come from the poorly known left bank (direction source to mouth) of the Congo River. One of these (Hylomyscus pygmaeus sp. nov.) is easily recognized, as it is tiny and significantly smaller than any known species of the genus; the second new species (Hylomyscus thornesmithae sp. nov.) is also small, and syntopic with the first. The third new species (Hylomyscus stanleyi sp. nov.), from the SW corner of Tanzania, is quite large and had been previously included within the hypodigm of Hylomyscus anselli following its recognition from within the synonymy of Hylomyscus denniae. The fourth species (Hylomyscus mpungamachagorum sp. nov.) is from Mahale Mountains National Park, western Tanzania. Our study reveals a much higher species diversity of the genus than previously known, providing insights into additional Afrotropical and Afromontane centers of endemism that require further exploration.