Part 2

Remarks.--Savage and Heyer (1967) provided evidence that A. callidryas taylori (Funkhouser) and A. helenae Cope were junior synonyms of A. callidryas (Cope).

Genus =Pachymedusa=, new genus

Type species, Agalychnis dacnicolor Cope, 1864.

Definition.--Fingers and toes having basal webs and lateral fringes; terminal discs large; first toe shorter than second and not opposable to others; skin smooth or shagreened, lacking osteoderms; paratoid glands present, diffuse; palpebral membrane reticulate; iris golden yellow with black reticulations; skull deep, depth more than 50 per cent of length; nasals large; frontoparietal fontanelle moderately large; quadratojugal robust; prevomerine teeth present.

Range.--Pacific slopes and lowlands from southern Sonora to the Isthmus of Tehuantepec, México.

Content.--Monotypic: dacnicolor Cope, 1864 [alcorni Taylor, 1952].

Remarks.--The generic name is derived from the Greek pachy meaning thick and the Greek Medousa (Latin, Medusa) in reference to Phyllomedusa; the sense implied is the heavy body of Pachymedusa dacnicolor.

Genus =Phyllomedusa= Wagler, 1830

Phyllomedusa Wagler, 1830 [Type species, Rana bicolor Boddaert, 1772].

Pithecopus Cope, 1866 [Type species, Phyllomedusa azurea Cope, 1862 (=Phyllomedusa hypochondrialis Daudin, 1803), by original designation].

Hylomantis Peters, 1872 [Type species Hylomantis aspera Peters, 1872, by monotypy].

Phrynomedusa Miranda-Ribeiro, 1923 [Type species, Phrynomedusa fimbriata Miranda-Ribeiro, 1923, by subsequent designation].

Bradymedusa Miranda-Ribeiro, 1926 [Type species, Bradymedusa moschada Miranda-Ribeiro, 1926 (=Phyllomedusa rohdei Mertens, 1926) by subsequent designation].

Definition.--Fingers and toes having greatly reduced webbing or lacking webs; terminal discs small; first toe shorter than, equal to, or longer than second, opposable or not; skin smooth or rugose having osteoderms or not; parotoid glands present, in most species, usually distinct and elevated; palpebral membrane not reticulate; iris uniformly silvery white to orange-bronze with black reticulations; skull moderate to deep, depth more than 38 per cent of length; nasals moderately small; frontoparietal fontanelle present, variable in size; quadratojugal reduced in some species; prevomerine teeth present or absent.

Range.--Low and moderate elevations in South America east of the Andes from the Caribbean (including Trinidad) to northern Argentina; Costa Rica and Panamá in Central America.

Content.--Thirty-one species [synonyms in brackets]: aspera (Peters, 1872); ayeaye (B. Lutz, 1966); bahiana A. Lutz, 1925; bicolor (Boddaert, 1772) [scleroderma Cope, 1868]; blombergi Funkhouser, 1957; boliviana Boulenger, 1902; buckleyi Boulenger, 1882; burmeisteri burmeisteri Boulenger, 1882; burmeisteri distincta B. Lutz, 1950; centralis Bokermann, 1965; cochranae Bokermann, 1966; coelestis (Cope, 1874); edentula Andersson, 1945; feltoni Shreve, 1935; fimbriata (Miranda-Ribeiro, 1923) [appendiculata A. Lutz, 1925]; guttata A. Lutz, 1925; hypochondrialis (Daudin, 1803) [azurea Cope, 1862; megacephala (Miranda-Ribeiro, 1926)]; iheringi Boulenger, 1885; lemur Boulenger, 1882; loris Boulenger, 1912; medinae Funkhouser, 1962; nicefori Barbour, 1926; orcesi Funkhouser, 1957; pailona Shreve, 1959; perlata Boulenger, 1882; rohdei Mertens, 1926 [moschada (Miranda-Ribeiro, 1926)]; sauvagei Boulenger, 1882 [rickettsii Günther, 1897]; tarsius (Cope, 1868); tomopterna (Cope, 1868) [palliata Peters, 1872]; trinitatis Mertens, 1926, vaillanti Boulenger, 1882, venusta Duellmann and Trueb, 1967.

Remarks.--Phyllomedusa includes 1) a series of large species (bicolor-burmeisteri) showing progressive specialization of the feet; 2) a series of small species having grasping feet (ayeaye, centralis, cochranae, guttata, hypochondrialis, and rohdei); 3) a series of small, relatively unspecialized species (lemur, loris, and medinae); and 4) several other species of questionable affinities. Lutz (1966) resurrected Cope's (1866) Pithecopus for 12 species (ayeaye, boliviana, burmeisteri, coelestis, hypochondrialis, nicefori, rohdei, sauvagei, tarsius, tomopterna, trinitatis, and vaillanti). Adequate material is not available for detailed study of all South American species; consequently, a firm classification cannot be established at this time. Nevertheless, it is obvious that Lutz's arrangement is unnatural. If subsequent investigations show, as seems likely, that the small specialized phyllomedusines are a natural phyletic unit, the generic name Pithecopus is available. However, species such as boliviana, burmeisteri, nicefori, and trinitatis do not belong in Pithecopus. As noted by Funkhouser (1962), the small, relatively unspecialized species (lemur, loris, and medinae) form a natural group; possibly this group should be accorded generic recognition. Until more evidence on the interspecific relationships is acquired, the maintenance of the current classification is desirable.

DISCUSSION

Noble (1931) considered the species of Phyllomedusa having opposable digits, reduced terminal discs, and no webbing to be advanced and such species as Agalychnis moreleti, calcarifer, and spurrelli to be primitive. Funkhouser (1957) followed Noble's suggestion and attempted to explain the evolution of the species of Phyllomedusa (sensu lato) by assuming that they evolved from an advanced Hyla-like ancestor. Therefore, she placed those species having large, fully webbed hands and feet near the base of her phylogenetic scheme and hypothesized that evolutionary sequences involved stages of reduction and eventual loss of webbing, followed by the development of grasping toes. Such an evolutionary history is highly unlikely. The Agalychnis phyletic line has one kind of specialization for an arboreal existence. It is contrary to evolutionary theory that a specialized group would evolve into a generalized form and then evolve new kinds of specializations to meet the needs imposed by the same environmental conditions affecting the earlier specialized group. A more reasonable hypothesis is that the evolution of opposable digits took place in a phyletic line that had as its ancestral stock a frog with generalized hands and feet. If this assumption is correct, Phyllomedusa and Agalychnis represent different phyletic lines; each exhibits divergent modes of adaptation for arboreal habits, whereas Pachymedusa probably remains relatively little changed from the basic phyllomedusine stock.

On the basis of modern distribution and areas of diversification alone (no fossils are known), it is evident that Phyllomedusa underwent its adaptive radiation in South America, Agalychnis evolved in Central America, and Pachymedusa ended up in western México. If we follow the Matthewsian concepts of the American herpetofauna outlined by Dunn (1931) and modified by Schmidt (1943) and Stuart (1950), Pachymedusa represents a "hanging-relict" of a group that moved southward. According to Savage's (1966) interpretation of the origins and history of the American herpetofauna, Agalychnis and Pachymedusa are members of the Mesoamerican fauna, and Phyllomedusa is part of the Neotropical fauna. Perhaps the phyllomedusines arose in South America; from there a primitive stock spread northward and survived as Pachymedusa in México, whereas the stock in Central America and South America evolved into Agalychnis and Phyllomedusa, respectively.

Evidently the primitive phyllomedusines evolved the habit of arboreal egg deposition and a walking gait; the latter is best developed in the small, highly specialized species of Phyllomedusa (Lutz, 1966). Probably the other divergent arboreal adaptations resulted from environmental stresses and competition. The generalized Pachymedusa inhabits relatively dry areas characterized by low forest. Throughout its range it coexists with no more than five other arboreal hylids. The species of Agalychnis live in rain forests and humid montane forests. In any given area one species of Agalychnis occurs sympatrically with no more than a dozen other arboreal hylids. With few exceptions the species of Agalychnis are more arboreal in their habits than are other hylids. The species of Phyllomedusa live in the same kinds of habitats as do those of Agalychnis, but throughout the ranges of most of the species of Phyllomedusa the diversity of arboreal hylids is much greater than in Central America. In the upper Amazon Basin as many as 35 hylids occur sympatrically. Many groups of Hyla in this area (for example, the Hyla boans and Hyla marmorata groups) are equally as arboreal in their habits as are the species of Agalychnis in Central America. Conceivably, competition within this array of tree frogs resulted in selection for modification of the extremities, thereby bringing about a different mode of climbing in Phyllomedusa. The walking gait already present in phyllomedusines provided a source for further modification, which resulted in the development of opposable digits and the associated lemuroid manner of climbing.

The known life histories of most species of Phyllomedusa, all species of Agalychnis, and that of Pachymedusa are similar. Characteristically the tadpoles are generalized pelagic types that develop in ponds, but at least some of the small specialized Phyllomedusa in southeastern Brazil have stream-adapted tadpoles with funnel-shaped mouths (Cochran, 1955; Bokermann, 1966). Knowledge of the life histories of the other species of Phyllomedusa should aid in the interpretation of the phylogenetic relationships of the several groups of frogs now assigned to that genus.

ACKNOWLEDGMENTS

I am grateful to Linda Trueb who provided the osteological data included, and who helped me in formulating some of the ideas expressed in the discussion. This paper is a result of investigations on hylid frogs supported by the National Science Foundation (NSF-GB-5818).

LITERATURE CITED

BOKERMANN, W. C. A 1966. A new Phyllomedusa from southeastern Brazil. Herpetologica, 22:293-297.

CEI, J. M 1963. Some precipitin tests and preliminary remarks on the systematic relationships of four South American families of frogs. Bull. Serological Mus., 30:4-6.

CEI, J. M. and V. ERSPAMER 1966. Biochemical taxonomy of South American amphibians by means of skin amines and polypeptides. Copeia, no. 1:74-8.