Probably the six species of _Smilisca_ were in existence by the end of the Pliocene; at that time a continuous land connection existed from Central America to South America. The climatic fluctuations in the Pleistocene, and the post-Wisconsin development of present climatic and vegetational patterns in Middle America, brought about the present patterns of distribution of the species. From its place of origin on the Caribbean lowlands of lower Central America, _S. phaeota_ dispersed northward into Nicaragua and southward along the Pacific slopes of northwestern South America. Perhaps in the late Pleistocene or in post-Wisconsin time when mesic conditions were more widespread than now, _S. phaeota_ moved onto the Pacific lowlands of Costa Rica. Its route could have been through the Arenal Depression. Subsequent aridity restricted its range on the Pacific lowlands to the Golfo Dulce region. Climatic fluctuation in northern Central America restricted the distribution of _S. cyanosticta_ to mesic habitats on the slopes of the Mexican and Guatemalan highlands and to certain humid areas on the lowlands. _Smilisca baudini_ was well adapted to sub-humid conditions, and the species dispersed northward to the Rio Grande Embayment and to the edge of the Sonoran Desert and southward into Costa Rica. In southern Mexico and Central America the species invaded mesic habitats. Consequently, in some areas it is sympatric with _S. cyanosticta_ and _phaeota_. _Smilisca puma_ dispersed northward onto the Caribbean lowlands of southern Nicaragua. Its southward movements probably were limited by the ridges of the Talamanca Range that extend to the Caribbean coast in the area of Punta Cahuita in Costa Rica. _Smilisca sila_ dispersed along the Pacific lowlands and slopes of the mountains from eastern Costa Rica and western Panama through eastern Panama to northern Colombia. Climatic fluctuation in the Pleistocene evidently provided sufficient altitudinal shifts in environments in the Talamanca Range to permit _S. sordida_ to move onto the Pacific slopes. From its upland distribution the species followed streams down to both the Caribbean and Pacific lowlands, where it is sympatric with _S. puma_ on the Caribbean lowlands and _S. sila_ on the Pacific lowlands. The evolution of the species-groups of _Smilisca_ was effected through isolation by physical barriers in the Cenozoic; the differentiation of the species was initiated by further isolation of populations by changes in physiography and climate. Present patterns of distribution resulted from Pleistocene and post-Wisconsin climatic changes. Today, sympatric species have different breeding habits and breeding calls which reinforce the differences in morphology. SUMMARY AND CONCLUSIONS