Among the eight adult members of the genus Rana that we examined, the proportion of total AP hair cells found in the caudal extensions ranged from 44% to 52%, with a mean of 47.5%. Considering the broad range of macro- and microhabitats occupied by the eight species combined with the plasticity of the AP plan seen in other taxa, this narrow spread seems remarkable. The sampled species are distributed broadly over the Hillis & Wilcox tree for New World Rana, suggesting the possibility of a common AP plan for that arm of the genus-- but beware the black swan.

Figure 2 from the same paper (Hillis & Wilcox, Phylogeny of the New World true frogs (Rana), Molecular Genetics and Evolution 34, 299-314, 2005).