Revalidation of Pristimantis brevicrus (Anura, Craugastoridae) with taxonomic comments on a widespread Amazonian direct-developing frog

Problems associated with delimiting species are particularly pronounced in taxa with high species-level diversity, as occurs in Pristimantis frogs. Herein, we resurrect Pristimantis brevicrus, nov. comb., from the synonymy of P. altamazonicus, a widespread species in the upper Amazon Basin, based on morphological, acoustic and genetic evidence. Both species are sympatric along the Upper Amazon Basin of Ecuador and northern Peru, up to ~1450 m. Phylogenetic analyses reveals that P. altamazonicus and P. brevicrus are sister taxa in a well-supported clade with P. diadematus and two unconfirmed candidate species. Pristimantis altamazonicus is distinguished from P. brevicrus by having a differentiated tympanic annulus, a smooth dorsum with scattered small tubercles towards the flanks, weakly areolate skin on the venter, red to bright orange groin with black mottling, on hidden surfaces of thighs (bluish-white to yellowish-white in P. brevicrus) of living specimens. The recognition of P. brevicrus and two unconfirmed candidate species suggest that the diversity of these frogs is inadequately understood, highlighting the need for more integrative taxonomic reviews of Amazonian amphibians.