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A Developmental Staging Table for Physalaemus biligonigerus (Cope, 1861) (Anura: Leptodactylidae)

Physalaemus biligonigerus is a leptodactylid frog that is widely distributed in southern South America and a common member of anuran assemblages that breed in temporary ponds near human settlements. Herein, we analyzed its embryonic and larval morphology through the completion of metamorphosis and constructed a normal table of development. In addition, the timing of development and growth data are provided. Development of P. biligonigerus from fertilization through metamorphosis takes 20–24 days. We recognized 46 discrete developmental stages on the basis of readily discerned, unambiguous, external traits that can be identified in preserved specimens. In contrast with the standard Gosner developmental table, we recognized several particularities in the development of this species. The staging criterion based on external gill morphology presented here is a novel approach to distinguish pre- and post-hatching stages, which could also be employed in other anuran species. We found that anal tube loss in P. biligonigerus occurs earlier than Gosner Stage 41; this trait is highly variable among species and should not be used as a standard criterion. Our analysis demonstrates the value of detailed specific staging tables to characterize anuran life cycles. Furthermore, we point out that the use of generalized standard tables might mask the richness of phenotypic variation during the ontogeny of anuran species.