Two New Microhylid Frogs of the Genus Rhombophryne with Superciliary Spines from the Tsaratanana Massif in Northern Madagascar

The Rhombophryne serratopalpebrosa (Guibé 1975) species complex consists of numerous cryptic narrow-mouthed frogs (Microhylidae) mostly restricted to northern Madagascar. We here provide an updated phylogeny of the genus Rhombophryne, and formally define the R. serratopalpebrosa group, characterized by the possession of small, fleshy superciliary spines. We describe two new species belonging to this group from the Tsaratanana Massif in northern Madagascar: Rhombophryne ornata sp. nov. and R. tany sp. nov. Both of the new species have fewer superciliary spines above each eye than any other member of the group (2 vs. 3–4). Rhombophryne ornata sp. nov. is unusual in having fairly elaborate dorsal markings, and is unique in having reddish thighs. In contrast, R. tany sp. nov. is a truly cryptic species characterized by a combination of characters unique within the R. serratopalpebrosa group. Micro-CT scans revealed differences between the skeletons of these species and other members of the group: the pubis is unossified in both species, and R. ornata sp. nov. lacks ossification in the epiphyses of its limb bones and in many of its small bones. We give a full osteological description of these frog species to facilitate ongoing research concerning this group. Genetic data suggest that these two syntopic species might be sister to each other, but they show a substantial genetic divergence of 3.9% and 8.4% uncorrected pairwise distance in the mitochondrial 16S rRNA and cytochrome oxidase subunit I genes, respectively. As these species have a limited extent of occurrence, and are known only from a single location in a forest that is declining in quality, we propose they be listed as Vulnerable B1ab(iii) on the International Union for Conservation of Nature Red List.