A Long Overlooked New Species of Fanged Frog, Genus Limnonectes (Amphibia: Anura: Dicroglossidae), from Luzon Island, Northern Philippines

We describe a new species of fanged frog (genus Limnonectes) from the foothills of two, inland, south-to-north oriented, parallel mountain ranges of Luzon Island of the northern Philippines. Although the new species broadly co-occurs with its closest relative at numerous localities within the Luzon Pleistocene aggregate island complex faunal region, it can be readily diagnosed from Limnonectes macrocephalus based on its unpigmented (white) ventral surfaces of terminal digital discs, its unexpanded or minimally expanded terminal digital discs, and an allometric growth pattern indicating evidence of sexual dimorphism at a smaller overall body size. The new species, which can also be identified by its divergent 16S ribosomal RNA mitochondrial gene sequence, possesses a curious distribution unlike the range of any Philippine endemic amphibian characterized to date: it is known from nine interior (inland) localities distributed between the two, parallel, south-to-north mountain chains (the Cordillera and Sierra Madre) which characterize mainland Luzon. We interpret the presence of two broadly sympatric, genetically divergent, strongly supported haplotype clades—which correspond to morphologically diagnosable phenotypes, using traditional discrete characters and allometric growth patterns—as prima facia evidence of two, independently evolving evolutionary lineages (species) of giant fanged frogs on Luzon. The description of another new species of large-bodied fanged frog on Luzon from multiple localities in close proximity to the capital city (Manila) emphasizes the degree to which even well-studied larger Philippine landmasses possess unrecognized and overlooked biodiversity.