Rheohyla

Duellman, William E., Marion, Angela B. & Hedges, Blair, 2016, Phylogenetics, classification, and biogeography of the treefrogs (Amphibia: Anura: Arboranae), Zootaxa 4104 (1), pp. 1-109 : 54

Hylidae : Hylinae

The divergence of North and Middle American hylid frogs from their relatives in South America was in the early Oligocene, 32.9 (30.2–35.6) Mya. Thus, hyline frogs were in Middle America in the early Miocene. Differentiation (crown node times) of the various genera occurred throughout the Miocene—as early as 26.1 Mya for the origin of Megastomatohyla to 13.1 Mya for the origin of Exerodonta . A major geographic divergence occurred in the early Miocene, 23.9 (22.3–25.6) Mya, when the clade now known as the Holarctic hylines diverged from the tropical hylines.

The geological uplifts and volcanism in Mexico and Central America began in the late Cretaceous and continues to the present. Only three clades of lowland inhabitants exist in the Middle American tropics; these are in a major clade that also includes Isthmohyla , which has stream-adapted tadpoles. The three lowland clades radiated (crown node times) in the mid-Miocene— Smilisca 13.2 (10.6–15.9) Mya, Tlalocohyla 15.5 (13.0–18.1) Mya, and a casque-headed clade ( Anotheca , Diaglena , and Triprion ) 14.3 (11.2–17.4) Mya. Slightly later the last clade differentiated into Diaglena and Triprion in xeric lowland habitats with tadpoles developing in temporary ponds, and the cloud forest-inhabitant, Anotheca , with tadpoles developing in tree holes. All species of Tlalocohyla range in the lowlands of Mexico; one species extends as far south as Costa Rica. Smilisca consists of six species ranging throughout Central America and tropical Mexico.

Currently there are 108 species of stream-breeding hylids in nine genera endemic to Middle America. The small stream-breeding Rheohyla diverged from the clade that became the large, arboreal hylines in the earliest Miocene, 23.0 (17.8–28.2) Mya. The fringe-limbed tree frogs of the genus Ecnomiohyla have disjunct distributions from Oaxaca, Mexico, through Panama, whereas Rheohyla occurs only in Mexico west of the Isthmus of Tehuantepec. Nested within the clade of inhabitants of Middle American lowlands is the stream-breading Isthmohyla , which consists of 15 species ranging discontinuously in highlands from Honduras to central Panama. Isthmohyla diverged from ancestral Smilisca in the early Miocene, 21.4 (18.7–24.1) Mya. All other streambreeding hylids belong to one major clade. Two of these clades possibly diverged in the late Oligocene. Megastomatohyla split with Charadrahyla about 26.1 (20.5–31.7) Mya in the Mexican highlands. The crown node time of the clade containing the genera Bromeliohyla , Duellmanohyla , and Ptychohyla , species occurring in the Central American highlands, is about 17.4 (14.9–19.9) Mya. These genera of yet undetermined affinities contain two bromeliad-breeding species in the genus Bromeliohyla and Duellmanohyla with eight species inhabiting the Central American highlands. That region is also inhabited by Ptychohyla with 13 species, some of which occur in southern Mexico.

The Isthmus of Tehuantepec in southern Mexico seems to have played a significant role in the differentiation and distribution of genera of stream-breeding hylines. Exerodonta split from the Plectrohyla-Sarcohyla lineage in the late Oligocene 27.5 (23.7–31.3) Mya. Exerodonta , which radiated (crown node time) in the mid-Miocene 13.1 (10.4–15.8) Mya, inhabits cloud forest and pine-oak forests at elevations of 450–2160 m; nine species occur west of the Isthmus of Tehuantepec and two live east of the isthmus. Likewise in the mid-Miocene, 15.7 (11.5–19.9) Mya, Charadrohyla was diversifying in the streams in southern Mexico, where five species live today; one other species occurs in Chiapas to the east of the Isthmus of Tehuantepec. The most striking example of diversification on opposite sides of the isthmus is Plectrohyla (18 species) in the northern Central American highlands to the east of the isthmus and Sarcohyla (24 species) in the Mexican highlands to the west of the isthmus. They split in the early mid-Miocene 18.6 (18.6–15.9) Mya. The times of diversification of ancestral stocks on either side of the isthmus coincide with the volcanism in the Miocene that elevated nuclear Central America and southern Mexico.