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PAGE INTRODUCTION 21 Acknowledgments 23 Field Studies in the Isthmus of Tehuantepec 23 Sources of Material 24
DESCRIPTION OF THE ISTHMUS OF TEHUANTEPEC 25 Physiography 25 Climate 28 Vegetation 29 The Sierra de los Tuxtlas 32
GAZETTEER 33
THE AMPHIBIAN FAUNA OF THE LOWLANDS 37 Composition of the Fauna 37 Ecology of the Fauna 38 Distribution of the Fauna 42
THE AMPHIBIAN FAUNA OF THE FOOTHILLS AND ADJACENT HIGHLANDS 44
ESTABLISHMENT OF PRESENT PATTERNS OF DISTRIBUTION 45
ACCOUNTS OF SPECIES 49
SUMMARY 68
LITERATURE CITED 69
INTRODUCTION
Few regions in Middle America are so important zoogeographically as is the Isthmus of Tehuantepec, that neck of land connecting North America with Central America, separating the Pacific Ocean from the Gulf of Mexico by a distance of only about 220 kilometers , and forming a low break between the highlands of M?xico and those of Central America. Before World War II the isthmus could be reached readily only by railroad or by ocean vessel to Salina Cruz or Coatzacoalcos. With the advent of roads, principally the Trans-isthmian Highway, vast areas of the interior of the isthmus became accessible to biologists. Nevertheless, long before roads were built in the isthmian region collectors and biologists visited it, especially the town of Tehuantepec, from which collections date back to the 1870's. Therefore, it is rather surprising that no attempt has been made to present a faunal list of the amphibians or reptiles of the isthmus. Ruthven summarized his collections from the vicinity of Cuatotolapam, Veracruz, and Hartweg and Oliver presented an annotated list of the species collected by them in the vicinity of Tehuantepec. In recent years there have been only a few papers reporting species from the isthmus . The zoogeographic significance of the Isthmus of Tehuantepec is exemplified by the works of Burt , Duellman , Gloyd , Oliver , and Stuart , who in their discussions of evolution and dispersal of various genera of reptiles, pointed out that the Isthmus of Tehuantepec was a region of zoogeographic importance.
Originally I intended to study the entire herpetofauna of the isthmus. But I have not had opportunity to study all of the reptiles, and I have not had the inclination to solve certain taxonomic problems concerning them. The amphibians that I collected, together with all other known specimens in museums, have been studied. Therefore, the present report is concerned only with the amphibians. Only the amphibians of the lowlands of the isthmus have been sampled adequately. Although I have commented on the highland species in the discussion of distribution, they are not included in the systematic section, which deals solely with the 36 species definitely known to occur in the lowlands of the isthmus.
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