Distinguishing features of the sub-Saharan frog genera Arthroleptis and Phrynobatrachus: a short guide for field and museum researchers

Typically small body size and similar external anatomy have made it difficult for researchers to distinguish between species of two distantly related, but often sympatric, African ranoid frog genera: Arthroleptis (Arthroleptidae) and Phrynobatrachus (Phrynobatrachidae). We define a suite of external morphological characters, extending beyond the traditionally used secondary sexual characteristics, that can be used to definitively distinguish between adult Arthroleptis and Phrynobatrachus. Photographs comparing absence, presence, and variation of morphological characters are included for clarification. Significant differences between body proportions (head width/snout–vent length) are also observed between these genera. Although smaller species might be more difficult to identify, larger species (> 30 mm snout–vent length) of Arthroleptis can be distinguished from Phrynobatrachus because of their relatively wider heads. We intend this to serve as a heuristic guide for both field- and museum-based researchers.