BehaviorThe tadpoles ofS. baudini,cyanosticta,phaeota, andpumaare pelagic inhabitants of shallow ponds. Early stages ofS. baudiniin which external gillsare present have been observed to hang vertically with the gills spread out at the surface of the water, a behavior noted by Zweifel (1964:206) in tadpoles ofPhrynohyas venulosa, which also develop in warm, standing water having a relatively low oxygen-tension. When disturbed the pelagic tadpoles usually dive and seek shelter amidst vegetation or in mud on the bottom. This behavior was observed inS. baudini,cyanosticta, andphaeotaby day and at night. No tadpoles ofS. pumawere observed by day; those seen at night were near the surface of small water-filled depressions in a grassy marsh; they responded to light by taking refuge in the dense grass. Perhaps tadpoles of this species are negatively phototactic and remain hidden by day.The stream-inhabiting tadpoles ofS. silaandsordidalive in clear pools in rocky streams, where they were observed to cling by their mouths to rocks in the stream and to seek shelter amidst pebbles or beneath rocks and leaves on the bottom. These tadpoles are not found in shallow riffles.We have not found tadpoles of two species ofSmiliscain the same body of water and therefore cannot offer observations on ecological relationships in sympatric situations.PHYLOGENETIC RELATIONSHIPSIdentifiable hylid remains are known from the Miocene to the Recent, but these fossils are mostly fragmentary and provide little useful information regarding the phylogenetic relationships of living genera. Frogs of the genusSmiliscaare generalized and show no striking adaptations, either in their structure or in their modes of life history.Interspecific RelationshipsIn attempting to understand the relationships of the species ofSmiliscawe have emphasized osteological characters. The phylogeny suggested by these characters is supported by other lines of evidence, including external morphology, tadpoles, and breeding calls.Our concept of the prototype of the genusSmiliscais a moderate-sized hylid having: (1) a well-developed frontoparietal fontanelle, (2) frontoparietal lacking lateral processes, (3) no bony squamosal-maxillary arch, (4) a fully ossified ethmoid, (5) paired subgular vocal sac, (6) moderately webbed fingers and toes, (7) relatively few supernumerary tubercles on the digits, (8) eggs deposited in clumps in ponds, (9) anteroventral mouth in tadpoles bordered by one row of labial papillae, but median part of upper lip bare, (10) tail relatively short and deep in tadpoles, and (11) a breeding call consisting of a series of like notes.Two phyletic lines evolved from this prototype. The first of these was the stock that gave rise to thebaudinigroup. The evolutionary changes that took place in this line included increase in size, development of a lateral curvature of the maxillary, and an increased amount of cranial ossification, especially in the dermal roofing bones. This phyletic line retained the larval characters and breeding call of the prototype. The second phyletic line gave rise to thesordidagroup and diverged from the prototype in the development of an angular maxillary and a breeding call consisting of a primary note followed by secondary notes. The frogs in this phyletic line retained the moderatesize of the prototype and did not develop additional dermal bone. Our concept of the phylogenetic relationships is shown graphically in Figure 17.Within thebaudinigroup one stock retained separate nasals and did not develop a bony squamosal-maxillary arch, but broad lateral processes developed on the frontoparietals. The tadpoles remained unchanged from the primitive type. This stock evolved intoS. phaeota. In the other stock the nasals became fully ossified and a bony squamosal-maxillary arch developed. One branch of this second stock retained tadpoles having only one row of labial papillae and did not develop lateral processes on the frontoparietals; this branch evolved intoS. cyanosticta. The other branch diverged and gave rise toS. baudiniby developing relatively shorter hind legs, large lateral processes on the frontoparietals, and tadpoles having two rows of labial papillae.Within thesordidagroup the cranial features remained unchanged in one line, which gave rise toS. sila, whereas in a second line the nasals were reduced, and their long axes shifted with the result that they are not parallel to the maxillaries; the amount of ossification of the ethmoid was reduced, and the tadpoles developed two rows of labial papillae. In this second line one branch retained the pond-breeding habits and gave rise toS. puma, whereas a second branch became adapted to stream-breeding and gave rise toS. sordida.Fig. 17.Hypothesized phylogenetic relationships of the species ofSmilisca.Certain aspects of this proposed phylogeny warrant further comment. Features such as the deposition of additional bone that roofs the skull or that forms lateral projections from the frontoparietals, like those inS. baudiniandphaeota, are minor alterations of dermal elements and not basic modificationsof the architecture of the skull. Consequently, we hypothesize the independent development of these dermal changes inS. baudiniandphaeota. Similar kinds of dermal modifications have evolved independently in many diverse groups of frogs.Likewise, we propose the parallel development of stream-adapted tadpoles inS. sordidaandsila; in both cases the tadpoles adapted to changing environmental conditions (see following section on evolutionary history). Tadpoles ofS. sordidaalready had two rows of labial papillae before entering the streams; subsequently the tadpoles developed complete rows of papillae, ventral mouths and long tails having low fins. Possibly the tadpoles ofS. silahad two rows of labial papillae prior to their adapting to stream conditions; in the process of adapting they developed ventral mouths and long tails having low fins. Similar modifications in tadpoles have occurred in many diverse groups of Middle American hylids, such asPlectrohyla,Ptychohyla, theHyla uranochroagroup, and theHyla taeniopusgroup.Our lack of concern about coloration is due to the fact that, with the exception of the blue spots on the flanks and posterior surfaces of the thighs in some species, the coloration ofSmilisca, consisting of a pattern of irregular dark marks on a paler dorsum and dark transverse bars on the limbs, is not much different from that of many other Neotropical hylids. Blue is a structural color, rare among Amphibia, which is achieved by the absence of lipophores above the guanophores. Thus, the incident light rays at the blue end of the spectrum are reflected by the guanophores without interference by an overlying yellow lipophore screen. According to Noble (1931), lipophores are capable of amoeboid movement that permits shifts in their positions, between or beneath the guanophores. We do not know whether this behavior of lipophores is widespread and is effected in response to environmental changes, or whether it is a genetically controlled attribute that is restricted in appearance. If the latter is the case we must assume that the prototype ofSmiliscapossessed such an attribute which was lost inS. baudini,phaeota, andpuma. The development of blue spots is not constant inS. sordidaandS. sila; inS. cyanostictathe spots range in color from blue to pale green.The coloration of the tadpoles is not distinctive, except for the presence of dorsal blotches on the tails ofS. silaandsordida. However, the similarity in pattern cannot be interpreted as indicating close relationships because nearly identical patterns are present inHyla legleriand some species ofProstherapis. This disruptive coloration seems to be directly associated with the pebble-bottom, stream-inhabiting tadpoles.In thebaudinigroup,S. phaeotaandcyanostictaare allopatric, whereasS. baudinioccurs sympatrically with both of those species. The call ofS. baudinidiffers notably from the calls ofS. phaeotaandcyanosticta, which are more nearly alike. Although in the phylogenetic scheme proposed hereS. silais considered to be more distantly related toS. pumathan isS. sordida, the calls ofS. silaandpumamore closely resemble one another than either resembles that ofS. sordida.Smilisca silaandpumaare allopatric, whereasS. sordidais broadly sympatric with both of those species. We assume that in their respective phyletic lines the differentiation of bothS. baudiniandsordidawas the result of genetic changes in geographically isolated populations. Subsequently, each species dispersed into areas inhabited by other members of their respective groups. Selection for differences in the breeding calls helped toreinforce other differences in the populations and thereby aided in maintaining specificity.Evolutionary HistoryWith respect to temporal and spatial aspects of evolution inSmilisca, we have tried to correlate the phylogenetic evidence onSmiliscawith the geologic data on Middle America presented by Lloyd (1963), Vinson and Brineman (1963), Guzmán and Cserna (1963), Maldonado-Koerdell (1964), and Whitmore and Stewart (1965). Likewise, we have borne in mind the evidence for, and ideas about, the evolution of the Middle American herpetofauna given by Dunn (1931b), Schmidt (1943), Stuart (1950, 1964) Duellman (1958, MS), and Savage (MS).According to Stuart's (1950) historical arrangement of the herpetofauna,Smiliscais a member of the Autochthonous Middle American Faunal Element, and according to Savage's (MS) arrangement the genus belongs to the Middle American Element, a fauna which was derived from a generalized tropical American unit that was isolated in tropical North America by the inundation of the Isthmian Link in early Tertiary, that developedin situin tropical North America, and that was restricted to Middle America by climatic change in the late Cenozoic.Savage (MS) relied on the paleogeographic maps of Lloyd (1963) to hypothesize the extent and centers of differentiation of the Middle American Faunal Element. According to Lloyd's concept, Middle America in the Miocene consisted of a broad peninsula extending southeastward to about central Nicaragua, separated from the Panamanian Spur of continental South America by shallow seas. A large island, the Talamanca Range, and remnants of the Guanarivas Ridge formed an archipelago in the shallow sea. The recent discovery of remains of mammals having definite North American affinities in the Miocene of the Canal Zone (Whitmore and Stewart, 1965) provides substantial evidence that at least a peninsula was continuous southeastward from Nuclear Central America to the area of the present Canal Zone in early mid-Miocene time. South America was isolated from Central America by the Bolivar Trough until late mid-Pliocene.Thus, in the mid-Tertiary the broad peninsula of Nuclear Central America, which consisted of low and moderately uplifted regions having a tropical mesic climate, provided the site for the evolution ofSmilisca. It is not possible to determine when the genus evolved, but to explain the differentiation of the species it is unnecessary to have the ancestralSmiliscapresent prior to the Miocene.We view the MioceneSmiliscaas the prototype described in the preceding section, and suppose that it lived in the mesic tropical environment of the eastern part of the Central American Peninsula (in what is now Costa Rica and western Panamá). Two stocks differentiated, probably in middle Miocene times; one of these, the ancestral stock of thebaudinigroup, was widespread on the Caribbean lowlands from the Nicaraguan Depression to the Bolivar Trough, and the other, the ancestral stock of thesordidagroup, was restricted to the Pacific lowlands of the same region. In late Miocene time the ancestral stock of thebaudinigroup dispersed northwestward around the deep embayment in the Nicaraguan depression into upper Central America (in what is now Honduras and Guatemala) and thence into southern México. Apparentlydifferentiation took place on each side of the Nicaraguan Depression; the frogs to the south of the depression evolved intoS. phaeota, whereas those to the north of the depression represented the stock from whichS. baudiniandcyanostictaarose. Prior to the uplift of the mountains in the late Miocene and the Pliocene thebaudini-cyanostictastock probably was widespread in northwestern Central America. The elevation of the mountains resulted in notable climatic changes, principally the development of sub-humid environments on the Pacific lowlands. The frogs living on the Pacific lowlands became adapted to sub-humid conditions and developed intoS. baudini. The stock on the Caribbean lowlands remained in mesic environments and evolved intoS. cyanosticta.Possibly in the middle Miocene before the Talamanca Range in Costa Rica and western Panamá was greatly uplifted, the ancestral stock of thesordidagroup invaded the Caribbean lowlands of what is now Costa Rica. The subsequent elevation of the Talamanca Range in the Pliocene effectively isolated the ancestral stock ofS. silaon the Pacific lowlands from thepuma-sordidastock on the Caribbean lowlands. The former was subjected to the sub-humid conditions which developed on the Pacific lowlands when the Talamanca Range was uplifted. It adapted to the sub-humid environment by living along streams and evolving stream-adapted tadpoles. On the Caribbean side of the Talamanca Range thepuma-sordidastock inhabited mesic environments. The stock that evolved intoS. pumaremained in the lowlands as a pond-breeding frog, whereas those frogs living on the slopes of the newly elevated mountains became adapted for their montane existence by developing stream-adapted tadpoles and thus differentiated intoS. sordida.Probably the six species ofSmiliscawere 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. phaeotadispersed 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. phaeotamoved 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 ofS. cyanostictato mesic habitats on the slopes of the Mexican and Guatemalan highlands and to certain humid areas on the lowlands.Smilisca baudiniwas 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 México and Central America the species invaded mesic habitats. Consequently, in some areas it is sympatric withS. cyanostictaandphaeota.Smilisca pumadispersed 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 siladispersed along the Pacific lowlands and slopes of the mountains from eastern Costa Rica and western Panamá througheastern Panamá to northern Colombia. Climatic fluctuation in the Pleistocene evidently provided sufficient altitudinal shifts in environments in the Talamanca Range to permitS. sordidato 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 withS. pumaon the Caribbean lowlands andS. silaon the Pacific lowlands.The evolution of the species-groups ofSmiliscawas 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 CONCLUSIONSThe genusSmiliscais composed of six species of tree frogs; each species is defined on the basis of adult morphology, larval characters, and breeding behavior. Keys are provided to aid in the identification of adults and of tadpoles.Analysis of the characters and examination of type specimens indicates that several currently-recognized taxa are synonymous, as follows:1.Hyla beltraniTaylor, 1942 =Smilisca baudini.2.Hyla gabbiCope, 1876 =Smilisca sordida.3.Hyla manisorumTaylor, 1954 =Smilisca baudini.4.Hyla nigripesCope, 1876 =Smilisca sordida.5.Hyla wellmanorumTaylor, 1952 =Smilisca puma.Smilisca phaeota cyanostictaSmith, 1953 is elevated to specific rank, and one new species,Smilisca sila, is named and described.The skeletal system of developmental stages and the adult ofSmilisca baudiniis described, and the skull is compared with that of other members of the genus.The tadpoles are described, compared, and illustrated; the larval development ofSmilisca phaeotais described.Breeding behavior and breeding calls are described and compared. Some species ofSmiliscahave breeding choruses. Two species,S. silaandsordida, breed in streams, whereas the others breed in ponds.The genus is considered to be part of the Middle American Faunal Element; the species are thought to have differentiated in response to ecological diversity and historical opportunities provided by Cenozoic changes in physiography and climate.LITERATURE CITEDBaird, S. F.1854. Descriptions of new genera and species of North American frogs. Proc. Acad. Nat. Sci. Philadelphia, 7:59-62. April 27.1859. Reptiles of the boundary. United States and Mexican boundary survey. Washington, D. C., p. 35, pl. 41.Baldauf, R. J.1959. Morphological criteria and their use in showing bufonid phylogeny. Jour. Morph., 104:527-560. May.Barbour, T.1923. Notes on reptiles and amphibians from Panama. Occas. Papers Mus. Zool. Univ. Michigan, 129:1-16. January 25.Blair, W. F.1959. Call structure and species groups in U. S. treefrogs (Hyla). Southwest. Nat., 3:77-89. June 1, 1959.1962. 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M.1961. Type specimens of reptiles and amphibians in the United States National Museum. Bull. U. S. Nat. Mus., 220:xv + 291 pp.Cope, E. D.1862. Catalogues of the reptiles obtained during the explorations of the Parana, Paraguay, Vermejo and Uraguay rivers.... Proc. Acad. Nat. Sci. Philadelphia, 14, pt. 9:346-359.1865. Third contribution to the herpetology of tropical America. Proc. Acad. Nat. Sci. Philadelphia, 17:185-198. October.1871. Ninth contribution to the herpetology of tropical America. Proc. Acad. Nat. Sci. Philadelphia, 23, pt. 2:200-224.Copland, S. J.1957. Australian tree frogs of the genusHyla. Proc. Linnean Soc. New South Wales, 82, pt. 1:9-108. September.Duellman, W. E.1956. The frogs of the hylid genusPhrynohyasFitzinger, 1843. Misc. Publ. Mus. Zool. Univ. Michigan, 96:1-47, pls. 1-6. February 21.1958. A monographic study of the colubrid snake genusLeptodeira. Bull. Amer. Mus. Nat. Hist., 114:1-152, pls. 1-31. February 24.1963a. A review of the Middle American tree frogs of the genus Ptychohyla. Univ. Kansas Publ. Mus. Nat. Hist., 15:297-349, pls. 11-18. October 18.1963b. A new species of tree frog, genusPhyllomedusa, from Costa Rica. Rev. Biol. Trop., 11(1):1-23. October.1964. A review of the frogs of the Hyla bistincta group. Univ. Kansas Publ. Mus. Nat. Hist., 15:469-491. March 2.1965. Frogs of theHyla taeniopusgroup. Copeia, no. 2:159-168. June 25.Duellman, W. E.andKlaas, L. T.1964. The biology of the hylid frogTriprion petasatus. Copeia, no. 2:308-321. June 30.Duméril, A. M. C.andBibron, G.1841. Erpétologie Générale ou histoire naturelle complète des reptiles, vol. 8, 792 pp.Dunn, E. R.1931a. The amphibians of Barro Colorado Island. Occas. Papers Boston Soc. Nat. Hist., 5:403-421. October 10.1931b. The herpetological fauna of the Americas. Copeia, no. 3:106-119. October 30.1944. Herpetology of the Bogotá area. Rev. Acad. Colombiana Cien. Exact., Fis. Nat., 6:68-81.Fouquette, M. J., Jr.1960. Isolating mechanisms in three sympatric tree frogs in the Canal Zone. Evolution, 14:484-497. December.Funkhouser, Anne1957. A review of the neotropical tree-frogs of the genusPhyllomedusa. Occas. Papers Nat. Hist. Mus. Stanford Univ., 5:1-89. April 1.Gadow, H.1908. Through southern Mexico. London, Witherby and Co. xvi + 527 pp.Gaige, H. T.,Hartweg, N.andStuart, L. C.1937. Notes on a collection of amphibians and reptiles from eastern Nicaragua. Occas. Papers Mus. Zool. Univ. Michigan, 357:1-18. October 26.Goin, C. J.1961. Synopsis of the genera of hylid frogs. Ann. Carnegie Mus., 36:5-18. July 14.Gosner, K. L.1960. A simplified table for staging anuran embryos and larvae with notes on identification. Herpetologica, 16:183-190. September 23.Griffiths, I.1959. The phylogeny ofSminthillus limbatusand the status of the Brachycephalidae (Amphibia, Salientia). Proc. Zool. Soc. London, 132:457-487, pls. 1-4.Guzmán, E. J.andCserna, Z.1963. Tectonic History of Mexico. Amer. Assoc. Petrol. Geol., Mem. 2:113-129.Hecht, M. K.1962. A reevaluation of the early history of the frogs. Part I. Syst. Zool., 11:39-44. March.1963. A reevaluation of the early history of the frogs. Part II. Syst. Zool., 12:20-35. March.Johnson, C.1959. Genetic incompatibility in the call races ofHyla versicolorLe Conte in Texas. Copeia, no. 4:327-335. December 30.Lloyd, J. J.1963. Tectonic history of the south Central-American Orogen. Amer. Assoc. Petrol. Geol., Mem. 2:88-100.Maldonado-Koerdell, M.1964. Geohistory and paleogeography of Middle America,inWauchope, R. and West, R. C. (Eds.). Handbook of Middle American Indians, vol. 1, Univ. Texas Press, Austin, 570 pp.Maslin, T. P.1963. Notes on some anuran tadpoles from Yucatán, México. Herpetologica, 19:122-128. July 3.Mittleman, M. B.andList, J. C.1963. The generic differentiation of the swamp treefrogs. Copeia, no. 2:80-83. May 29.Noble, G. K.1931. The biology of the amphibia. McGraw Hill, New York, 577 pp.Orton, G. L.1957. The bearing of larval evolution on some problems in frog classification. Syst. Zool., 6:79-86. June.Peters, W.1863. Mittheilungen uber neue Batrachier. Monats. Konigl. Akad. Wiss. Berlin, pp. 445-471.1873. Uber eine neue Schildkrötenart,Cinosternon Effeldtiiund einige andere neue oder weniger bekannte Amphibien. Monats. Konigl. Akad. Wiss. Berlin, pp. 603-618, pl. 5. October 16.Rivero, J. A.1961. Salientia of Venezuela. Bull. Comp. Zool., 126:1-207. November.Savage, J. M.andCarvalho, A. L.1953. The family position of Neotropical frogs currently referred to the genusPseudis. Zoologica, 38:193-200.Schmidt, K. P.1941. The amphibians and reptiles of British Honduras. Zool. Ser. Field Mus. Nat. Hist., 22:475-510. December 30.1943. Corollary and commentary for "Climate and Evolution." Amer. Midl. Nat., 30:241-253. July.Schmidt, O.1857. Diagnosen neuer Frösche des zoologischen Cabinets zu Krakau. Sitzungb. Konigl. Akad. Wiss. Math.-Natur. Cl., 24(1):10-15. March.1858. Deliciae Herpetogicae Musei Zoologici Cracoviensis. Denkschr. K. K. Akad. Wiss. Math.-Natur. Cl., 14(2):237-258, pls. 1-3.Smith, H. M.1953. A new subspecies of the treefrogHyla phaeotaCope of Central America. Herpetologica, 8:150-152. January 30.Smith, H. M.andTaylor, E. H.1950. Type localities of Mexican reptiles and amphibians. Univ. Kansas Sci. Bull., 33:313-380. March 20.Starrett, P.1960. A redefinition of the genusSmilisca. Copeia, no. 4:300-304. December 30.Stebbins, R. C.andHendrickson, J. R.1959. Field studies of amphibians in Colombia, South America. Univ. California Publ. Zool., 56:497-540. February 17.Stokely, P. S.andList, J. C.1954. The progress of ossification in the skull of the cricketfrogPseudacris nigrita triseriata. Copeia, no. 3:211-217. July 29.Stuart, L. C.1935. A contribution to a knowledge of the herpetology of a portion of the savanna region of central Petén, Guatemala. Misc. Publ. Mus. Zool. Univ. Michigan, 29:1-56, pls. 1-4, 1 map. October 1.1948. The amphibians and reptiles of Alta Verapaz, Guatemala. Misc. Publ. Mus. Zool. Univ. Michigan, 69:1-109. June 12.1950. A geographic study of the herpetofauna of Alta Verapaz, Guatemala. Contr. Lab. Vert. Biol., 45:1-77, pls. 1-9, 1 map. May.1954. Herpetofauna of the southeastern highlands of Guatemala. Contr. Lab. Vert. Biol., 68:1-65, pls. 1-4. November.1958. A study of the herpetofauna of the Uaxactun-Tikal area of northern El Petén, Guatemala. Contr. Lab. Vert. Biol., 75:1-30. June.1961. Some observations on the natural history of tadpoles ofRhinophrynus dorsalisDumériland Bibron. Herpetologica, 17:73-79. July 11.1964. Fauna of Middle America,inWauchope, R. and West, R. C. (Eds.). Handbook of Middle American Indians, vol. 1, Univ. Texas Press, Austin, 570 pp.Taylor, E. H.1942. New Caudata and Salientia from México. Univ. Kansas Sci. Bull., 28:295-323. November 15.1952. The frogs and toads of Costa Rica. Univ. Kansas Sci. Bull., 35:577-942. July 1.1954. Additions to the known herpetological fauna of Costa Rica with comments on other species. No. I. Univ. Kansas Sci. Bull., 36:597-639. June 1.Taylor, E. H.andSmith, H. M.1945. Summary of the collections of amphibians made in México under the Walter Rathbone Bacon Traveling Scholarship. Proc. U. S. Natl. Mus., 95:521-613, pls. 18-32. June 30.Tihen, J. A.1962. Osteological observations on New World Bufo. Amer. Midl. Nat., 67:157-183. January.1965. Evolutionary trends in frogs. Amer. Zoologist, 5:309-318.Vinson, G. L.andBrineman, J. H.1963. Nuclear Central America, hub of Antillean Transverse Belt. Amer. Assoc. Petrol. Geol., Mem. 2:101-112.Whitmore, F. C., Jr.andStewart, R. H.1965. Miocene mammals and Central American seaways. Science, 148:180-185. April 9.Zweifel, R. G.1956. Two pelobatid frogs from the Tertiary of North America and their relationships to fossil and Recent forms. Amer. Mus. Novitates, 1762:1-45. April 6.1958. Results of the Archbold Expeditions. No. 78. Frogs of the Papuan hylid genusNyctimystes. Amer. Mus. Novitates, 1896:1-51. July 22.1964. Life history ofPhrynohyas venulosa(Salientia: Hylidae) in Panamá. Copeia, no. 1:201-208. March 26.Transmitted March 14, 1966.31-3430UNIVERSITY OF KANSAS PUBLICATIONSMUSEUM OF NATURAL HISTORYInstitutional libraries interested in publications exchange may obtain this series by addressing the Exchange Librarian, University of Kansas Library, Lawrence, Kansas. Copies for individuals, persons working in a particular field of study, may be obtained by addressing instead the Museum of Natural History, University of Kansas, Lawrence, Kansas. When individuals request copies from the Museum, 25 cents should be included, for each 100 pages or part thereof, for the purpose of defraying the costs of wrapping and mailing. 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Eaton, Jr., and Peggy Lou Stewart. Pp. 217-240, 12 figures in text. May 2, 1960.5.Natural history of the Bell Vireo, Vireo bellii Audubon. By Jon C. Barlow. Pp. 241-296, 6 figures in text. March 7, 1962.6.Two new pelycosaurs from the lower Permian of Oklahoma. By Richard C. Fox. Pp. 297-307, 6 figures in text. May 21, 1962.7.Vertebrates from the barrier island of Tamaulipas, México. By Robert K. Selander, Richard F. Johnston, B. J. Wilks, and Gerald G. Raun. Pp. 309-345, pls. 5-8. June 18, 1962.8.Teeth of edestid sharks. By Theodore H. Eaton, Jr. Pp. 347-362, 10 figures in text. October 1, 1962.9.Variation in the muscles and nerves of the leg in two genera of grouse (Tympanuchus and Pedioecetes). By E. Bruce Holmes. Pp. 363-474, 20 figures in text. October 25, 1963. $1.00.10.A new genus of Pennsylvanian fish (Crossopterygii, Coelacanthiformes) from Kansas. By Joan Echols. Pp. 475-501, 7 figures in text. October 25, 1963.11.Observations on the Mississippi kite in southwestern Kansas. By Henry S. Fitch. Pp. 503-519. October 25, 1963.12.Jaw musculature of the Mourning and White-winged doves. By Robert L. Merz. Pp. 521-551, 22 figures in text. October 25, 1963.13.Thoracic and coracoid arteries in two families of birds, Columbidae and Hirundinidae. By Marion Anne Jenkinson. Pp. 553-573, 7 figures in text. March 2, 1964.14.The breeding birds of Kansas. By Richard F. Johnston. Pp. 575-655, 10 figures in text. May 18, 1964. 75 cents.15.The adductor muscles of the jaw in some primitive reptiles. By Richard C. Fox. Pp. 657-680, 11 figures in text. May 18, 1964.Index. Pp. 681-694.Vol. 13.1.Five natural hybrid combinations in minnows (Cyprinidae). By Frank B. Cross and W. L. Minckley. Pp. 1-18. June 1, 1960.2.A distributional study of the amphibians of the Isthmus of Tehuantepec, México. By William E. Duellman. Pp. 19-72, pls. 1-8, 3 figures in text. August 16, 1960. 50 cents.3.A new subspecies of the slider turtle (Pseudemys scripta) from Coahulia, México. By John M. 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April 30, 1962.12.Noteworthy mammals from Sinaloa, Mexico. By J. Knox Jones, Jr., Ticul Alvarez, and M. Raymond Lee. Pp. 145-159, 1 figure in text. May 18, 1962.13.A new bat (Myotis) from Mexico. By E. Raymond Hall. Pp. 161-164, 1 figure in text. May 21, 1962.*14.The mammals of Veracruz. By E. Raymond Hall and Walter W. Dalquest. Pp. 165-362, 2 figures. May 20, 1963. $2.00.15.The recent mammals of Tamaulipas, México. By Ticul Alvarez. Pp. 363-473, 5 figures in text. May 20, 1963. $1.00.16.A new subspecies of the fruit-eating bat, Sturnira ludovici, from western Mexico. By J. Knox Jones, Jr., and Gary L. Phillips. Pp. 475-481, 1 figure in text. March 2, 1964.17.Records of the fossil mammal Sinclairella, Family Apatemyidae, from the Chadronian and Orellan. By William A. Clemens, Jr. Pp. 483-491, 2 figures in text. March 2, 1964.18.The mammals of Wyoming. By Charles A. Long. Pp. 493-758, 82 figures in text. July 6, 1965. $3.00.Index. Pp. 759-784.Vol. 15.1.The amphibians and reptiles of Michoacán, México. By William E. Duellman. Pp. 1-148, pls. 1-6, 11 figures in text. December 20, 1961. $1.50.2.Some reptiles and amphibians from Korea. By Robert G. Webb, J. Knox Jones, Jr., and George W. Byers. Pp. 149-173. January 31, 1962.3.A new species of frog (Genus Tomodactylus) from western México. By Robert G. Webb. Pp. 175-181, 1 figure in text. March 7, 1962.4.Type specimens of amphibians and reptiles in the Museum of Natural History, the University of Kansas. By William E. Duellman and Barbara Berg.Pp. 183-204. October 26, 1962.5.Amphibians and Reptiles of the Rainforests of Southern El Petén, Guatemala. By William E. Duellman. Pp. 205-249, pls. 7-10, 6 figures in text. October 4, 1963.6.A revision of snakes of the genus Conophis (Family Colubridae, from Middle America). By John Wellman. Pp. 251-295, 9 figures in text. October 4, 1963.7.A review of the Middle American tree frogs of the genus Ptychohyla. By William E. 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Pp. 627-709, pls. 29-36, 5 figures in text. December 30, 1965.15.Amphibians and reptiles of Mesa Verde National Park, Colorado. By Charles L. Douglas. Pp. 711-744, pls. 37 and 38, 6 figures in text. March 7, 1966.Index in preparation.Vol. 16.1.Distribution and taxonomy of mammals of Nebraska. By J. Knox Jones, Jr. Pp. 1-356, plates 1-4, 82 figures in text. October 1, 1964. $3.50.2.Synopsis of the lagomorphs and rodents of Korea. By J. Knox Jones, Jr., and David H. Johnson. Pp. 357-407. February 12, 1965.3.Mammals from Isla Cozumel, Mexico, with description of a new species of harvest mouse. By J. Knox Jones, Jr. and Timothy E. Lawlor. Pp. 409-419, 1 figure in text. April 13, 1965.4.The Yucatan deer mouse, Peromyscus yucatanicus. By Timothy E. Lawlor. Pp. 421-438, 2 figures in text. July 20, 1965.5.Bats from Gautemala. By J. Knox Jones, Jr. Pp. 439-472. April 18, 1966.More numbers will appear in volume 16.Vol. 17.1.Localities of fossil vertebrates obtained from the Niobrara Formation (Cretaceous) of Kansas. By David Bardack. Pp. 1-14. January 22, 1965.2.Chorda tympani branch of the facial nerve in the middle ear of tetrapods. By Richard C. Fox. Pp. 15-21. June 22, 1965.3.Fishes of the Kansas River System in relation to zoogeography of the Great Plains. By Artie L. Metcalf. Pp. 23-189, 4 figures in text, 51 maps. March 24, 1966.4.Factors affecting growth and production of channel catfish, Ictalurus punctatus. By Bill A. Simco and Frank B. Cross. Pp. 191-256, 13 figures in text. June 6, 1966.5.A new species of fringe-limbed tree frog, genus Hyla, from Darién, Panamá. By William E. Duellman. Pp. 257-262, 1 figure in text. June 17, 1966.6.Taxonomic notes on some Mexican and Central American hylid frogs. By William E. Duellman. Pp. 263-279. June 17, 1966.7.Neotropical hylid frogs, genus Smilisca. By William E. Duellman and Linda Trueb. Pp. 281-375, pls. 1-12, 17 figures in text. July 14, 1966.More numbers will appear in volume 17.
Behavior
The tadpoles ofS. baudini,cyanosticta,phaeota, andpumaare pelagic inhabitants of shallow ponds. Early stages ofS. baudiniin which external gillsare present have been observed to hang vertically with the gills spread out at the surface of the water, a behavior noted by Zweifel (1964:206) in tadpoles ofPhrynohyas venulosa, which also develop in warm, standing water having a relatively low oxygen-tension. When disturbed the pelagic tadpoles usually dive and seek shelter amidst vegetation or in mud on the bottom. This behavior was observed inS. baudini,cyanosticta, andphaeotaby day and at night. No tadpoles ofS. pumawere observed by day; those seen at night were near the surface of small water-filled depressions in a grassy marsh; they responded to light by taking refuge in the dense grass. Perhaps tadpoles of this species are negatively phototactic and remain hidden by day.
The stream-inhabiting tadpoles ofS. silaandsordidalive in clear pools in rocky streams, where they were observed to cling by their mouths to rocks in the stream and to seek shelter amidst pebbles or beneath rocks and leaves on the bottom. These tadpoles are not found in shallow riffles.
We have not found tadpoles of two species ofSmiliscain the same body of water and therefore cannot offer observations on ecological relationships in sympatric situations.
PHYLOGENETIC RELATIONSHIPS
Identifiable hylid remains are known from the Miocene to the Recent, but these fossils are mostly fragmentary and provide little useful information regarding the phylogenetic relationships of living genera. Frogs of the genusSmiliscaare generalized and show no striking adaptations, either in their structure or in their modes of life history.
Interspecific Relationships
In attempting to understand the relationships of the species ofSmiliscawe have emphasized osteological characters. The phylogeny suggested by these characters is supported by other lines of evidence, including external morphology, tadpoles, and breeding calls.
Our concept of the prototype of the genusSmiliscais a moderate-sized hylid having: (1) a well-developed frontoparietal fontanelle, (2) frontoparietal lacking lateral processes, (3) no bony squamosal-maxillary arch, (4) a fully ossified ethmoid, (5) paired subgular vocal sac, (6) moderately webbed fingers and toes, (7) relatively few supernumerary tubercles on the digits, (8) eggs deposited in clumps in ponds, (9) anteroventral mouth in tadpoles bordered by one row of labial papillae, but median part of upper lip bare, (10) tail relatively short and deep in tadpoles, and (11) a breeding call consisting of a series of like notes.
Two phyletic lines evolved from this prototype. The first of these was the stock that gave rise to thebaudinigroup. The evolutionary changes that took place in this line included increase in size, development of a lateral curvature of the maxillary, and an increased amount of cranial ossification, especially in the dermal roofing bones. This phyletic line retained the larval characters and breeding call of the prototype. The second phyletic line gave rise to thesordidagroup and diverged from the prototype in the development of an angular maxillary and a breeding call consisting of a primary note followed by secondary notes. The frogs in this phyletic line retained the moderatesize of the prototype and did not develop additional dermal bone. Our concept of the phylogenetic relationships is shown graphically in Figure 17.
Within thebaudinigroup one stock retained separate nasals and did not develop a bony squamosal-maxillary arch, but broad lateral processes developed on the frontoparietals. The tadpoles remained unchanged from the primitive type. This stock evolved intoS. phaeota. In the other stock the nasals became fully ossified and a bony squamosal-maxillary arch developed. One branch of this second stock retained tadpoles having only one row of labial papillae and did not develop lateral processes on the frontoparietals; this branch evolved intoS. cyanosticta. The other branch diverged and gave rise toS. baudiniby developing relatively shorter hind legs, large lateral processes on the frontoparietals, and tadpoles having two rows of labial papillae.
Within thesordidagroup the cranial features remained unchanged in one line, which gave rise toS. sila, whereas in a second line the nasals were reduced, and their long axes shifted with the result that they are not parallel to the maxillaries; the amount of ossification of the ethmoid was reduced, and the tadpoles developed two rows of labial papillae. In this second line one branch retained the pond-breeding habits and gave rise toS. puma, whereas a second branch became adapted to stream-breeding and gave rise toS. sordida.
Fig. 17.Hypothesized phylogenetic relationships of the species ofSmilisca.
Fig. 17.Hypothesized phylogenetic relationships of the species ofSmilisca.
Certain aspects of this proposed phylogeny warrant further comment. Features such as the deposition of additional bone that roofs the skull or that forms lateral projections from the frontoparietals, like those inS. baudiniandphaeota, are minor alterations of dermal elements and not basic modificationsof the architecture of the skull. Consequently, we hypothesize the independent development of these dermal changes inS. baudiniandphaeota. Similar kinds of dermal modifications have evolved independently in many diverse groups of frogs.
Likewise, we propose the parallel development of stream-adapted tadpoles inS. sordidaandsila; in both cases the tadpoles adapted to changing environmental conditions (see following section on evolutionary history). Tadpoles ofS. sordidaalready had two rows of labial papillae before entering the streams; subsequently the tadpoles developed complete rows of papillae, ventral mouths and long tails having low fins. Possibly the tadpoles ofS. silahad two rows of labial papillae prior to their adapting to stream conditions; in the process of adapting they developed ventral mouths and long tails having low fins. Similar modifications in tadpoles have occurred in many diverse groups of Middle American hylids, such asPlectrohyla,Ptychohyla, theHyla uranochroagroup, and theHyla taeniopusgroup.
Our lack of concern about coloration is due to the fact that, with the exception of the blue spots on the flanks and posterior surfaces of the thighs in some species, the coloration ofSmilisca, consisting of a pattern of irregular dark marks on a paler dorsum and dark transverse bars on the limbs, is not much different from that of many other Neotropical hylids. Blue is a structural color, rare among Amphibia, which is achieved by the absence of lipophores above the guanophores. Thus, the incident light rays at the blue end of the spectrum are reflected by the guanophores without interference by an overlying yellow lipophore screen. According to Noble (1931), lipophores are capable of amoeboid movement that permits shifts in their positions, between or beneath the guanophores. We do not know whether this behavior of lipophores is widespread and is effected in response to environmental changes, or whether it is a genetically controlled attribute that is restricted in appearance. If the latter is the case we must assume that the prototype ofSmiliscapossessed such an attribute which was lost inS. baudini,phaeota, andpuma. The development of blue spots is not constant inS. sordidaandS. sila; inS. cyanostictathe spots range in color from blue to pale green.
The coloration of the tadpoles is not distinctive, except for the presence of dorsal blotches on the tails ofS. silaandsordida. However, the similarity in pattern cannot be interpreted as indicating close relationships because nearly identical patterns are present inHyla legleriand some species ofProstherapis. This disruptive coloration seems to be directly associated with the pebble-bottom, stream-inhabiting tadpoles.
In thebaudinigroup,S. phaeotaandcyanostictaare allopatric, whereasS. baudinioccurs sympatrically with both of those species. The call ofS. baudinidiffers notably from the calls ofS. phaeotaandcyanosticta, which are more nearly alike. Although in the phylogenetic scheme proposed hereS. silais considered to be more distantly related toS. pumathan isS. sordida, the calls ofS. silaandpumamore closely resemble one another than either resembles that ofS. sordida.Smilisca silaandpumaare allopatric, whereasS. sordidais broadly sympatric with both of those species. We assume that in their respective phyletic lines the differentiation of bothS. baudiniandsordidawas the result of genetic changes in geographically isolated populations. Subsequently, each species dispersed into areas inhabited by other members of their respective groups. Selection for differences in the breeding calls helped toreinforce other differences in the populations and thereby aided in maintaining specificity.
Evolutionary History
With respect to temporal and spatial aspects of evolution inSmilisca, we have tried to correlate the phylogenetic evidence onSmiliscawith the geologic data on Middle America presented by Lloyd (1963), Vinson and Brineman (1963), Guzmán and Cserna (1963), Maldonado-Koerdell (1964), and Whitmore and Stewart (1965). Likewise, we have borne in mind the evidence for, and ideas about, the evolution of the Middle American herpetofauna given by Dunn (1931b), Schmidt (1943), Stuart (1950, 1964) Duellman (1958, MS), and Savage (MS).
According to Stuart's (1950) historical arrangement of the herpetofauna,Smiliscais a member of the Autochthonous Middle American Faunal Element, and according to Savage's (MS) arrangement the genus belongs to the Middle American Element, a fauna which was derived from a generalized tropical American unit that was isolated in tropical North America by the inundation of the Isthmian Link in early Tertiary, that developedin situin tropical North America, and that was restricted to Middle America by climatic change in the late Cenozoic.
Savage (MS) relied on the paleogeographic maps of Lloyd (1963) to hypothesize the extent and centers of differentiation of the Middle American Faunal Element. According to Lloyd's concept, Middle America in the Miocene consisted of a broad peninsula extending southeastward to about central Nicaragua, separated from the Panamanian Spur of continental South America by shallow seas. A large island, the Talamanca Range, and remnants of the Guanarivas Ridge formed an archipelago in the shallow sea. The recent discovery of remains of mammals having definite North American affinities in the Miocene of the Canal Zone (Whitmore and Stewart, 1965) provides substantial evidence that at least a peninsula was continuous southeastward from Nuclear Central America to the area of the present Canal Zone in early mid-Miocene time. South America was isolated from Central America by the Bolivar Trough until late mid-Pliocene.
Thus, in the mid-Tertiary the broad peninsula of Nuclear Central America, which consisted of low and moderately uplifted regions having a tropical mesic climate, provided the site for the evolution ofSmilisca. It is not possible to determine when the genus evolved, but to explain the differentiation of the species it is unnecessary to have the ancestralSmiliscapresent prior to the Miocene.
We view the MioceneSmiliscaas the prototype described in the preceding section, and suppose that it lived in the mesic tropical environment of the eastern part of the Central American Peninsula (in what is now Costa Rica and western Panamá). Two stocks differentiated, probably in middle Miocene times; one of these, the ancestral stock of thebaudinigroup, was widespread on the Caribbean lowlands from the Nicaraguan Depression to the Bolivar Trough, and the other, the ancestral stock of thesordidagroup, was restricted to the Pacific lowlands of the same region. In late Miocene time the ancestral stock of thebaudinigroup dispersed northwestward around the deep embayment in the Nicaraguan depression into upper Central America (in what is now Honduras and Guatemala) and thence into southern México. Apparentlydifferentiation took place on each side of the Nicaraguan Depression; the frogs to the south of the depression evolved intoS. phaeota, whereas those to the north of the depression represented the stock from whichS. baudiniandcyanostictaarose. Prior to the uplift of the mountains in the late Miocene and the Pliocene thebaudini-cyanostictastock probably was widespread in northwestern Central America. The elevation of the mountains resulted in notable climatic changes, principally the development of sub-humid environments on the Pacific lowlands. The frogs living on the Pacific lowlands became adapted to sub-humid conditions and developed intoS. baudini. The stock on the Caribbean lowlands remained in mesic environments and evolved intoS. cyanosticta.
Possibly in the middle Miocene before the Talamanca Range in Costa Rica and western Panamá was greatly uplifted, the ancestral stock of thesordidagroup invaded the Caribbean lowlands of what is now Costa Rica. The subsequent elevation of the Talamanca Range in the Pliocene effectively isolated the ancestral stock ofS. silaon the Pacific lowlands from thepuma-sordidastock on the Caribbean lowlands. The former was subjected to the sub-humid conditions which developed on the Pacific lowlands when the Talamanca Range was uplifted. It adapted to the sub-humid environment by living along streams and evolving stream-adapted tadpoles. On the Caribbean side of the Talamanca Range thepuma-sordidastock inhabited mesic environments. The stock that evolved intoS. pumaremained in the lowlands as a pond-breeding frog, whereas those frogs living on the slopes of the newly elevated mountains became adapted for their montane existence by developing stream-adapted tadpoles and thus differentiated intoS. sordida.
Probably the six species ofSmiliscawere 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. phaeotadispersed 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. phaeotamoved 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 ofS. cyanostictato mesic habitats on the slopes of the Mexican and Guatemalan highlands and to certain humid areas on the lowlands.Smilisca baudiniwas 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 México and Central America the species invaded mesic habitats. Consequently, in some areas it is sympatric withS. cyanostictaandphaeota.
Smilisca pumadispersed 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 siladispersed along the Pacific lowlands and slopes of the mountains from eastern Costa Rica and western Panamá througheastern Panamá to northern Colombia. Climatic fluctuation in the Pleistocene evidently provided sufficient altitudinal shifts in environments in the Talamanca Range to permitS. sordidato 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 withS. pumaon the Caribbean lowlands andS. silaon the Pacific lowlands.
The evolution of the species-groups ofSmiliscawas 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
The genusSmiliscais composed of six species of tree frogs; each species is defined on the basis of adult morphology, larval characters, and breeding behavior. Keys are provided to aid in the identification of adults and of tadpoles.
Analysis of the characters and examination of type specimens indicates that several currently-recognized taxa are synonymous, as follows:
1.Hyla beltraniTaylor, 1942 =Smilisca baudini.2.Hyla gabbiCope, 1876 =Smilisca sordida.3.Hyla manisorumTaylor, 1954 =Smilisca baudini.4.Hyla nigripesCope, 1876 =Smilisca sordida.5.Hyla wellmanorumTaylor, 1952 =Smilisca puma.
Smilisca phaeota cyanostictaSmith, 1953 is elevated to specific rank, and one new species,Smilisca sila, is named and described.
The skeletal system of developmental stages and the adult ofSmilisca baudiniis described, and the skull is compared with that of other members of the genus.
The tadpoles are described, compared, and illustrated; the larval development ofSmilisca phaeotais described.
Breeding behavior and breeding calls are described and compared. Some species ofSmiliscahave breeding choruses. Two species,S. silaandsordida, breed in streams, whereas the others breed in ponds.
The genus is considered to be part of the Middle American Faunal Element; the species are thought to have differentiated in response to ecological diversity and historical opportunities provided by Cenozoic changes in physiography and climate.
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