Members of the Hyla bistincta group and the species of Plectrohyla closely resemble each other in osteology and body form of the adults and in structure of the tadpoles. This resemblance suggests a close relationship between the two groups. Plectrohyla apparently evolved from an ancestral stock resembling the extant Hyla bistincta. Probably this stock gave rise independently to Plectrohyla and to the Hyla robertsorum-pachyderma-crassa complex. In the former the voice was retained, and a projecting prepollex spine developed, whereas in the latter the voice was lost, and the prepollex spine did not project. Plectrohyla lives in mountain streams in the Chiapan-Guatemalan highlands; the Hyla robertsorum-pachyderma-crassa complex inhabits similar environments in the Sierra Madre Oriental in México. Hyla charadricola also lives in the Sierra Madre Oriental, whereas Hyla bistincta is widespread in the mountains of México southeastward to the Isthmus of Tehuantepec.
LITERATURE CITED
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Brocchi, P.
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Duellman, W. E.
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