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PAGE INTRODUCTION 207 Acknowledgments 208

DESCRIPTION OF AREA 208 Physiography 209 Climate 209 Vegetation 209

GAZETTEER 210

THE HERPETOFAUNA OF THE RAINFOREST 211 Composition of the Fauna 212 Ecology of the Herpetofauna 212 Relationships of the Fauna 217

ACCOUNTS OF SPECIES 218

HYPOTHETICAL LIST OF SPECIES 246

SUMMARY 247

LITERATURE CITED 247

INTRODUCTION

Early in 1960 an unusual opportunity arose to carry on biological field work in the midst of virgin rainforest in southern El Pet?n, Guatemala. At that time the Ohio Oil Company of Guatemala had an air strip and camp at Chinaj?, from which place the company was constructing a road northward through the forest. In mid-February, 1960, J. Knox Jones, Jr. and I flew into El Pet?n to collect and study mammals, reptiles, and amphibians. While enjoying the comforts of the fine field camp at Chinaj?, we worked in the surrounding forest and availed ourselves of the opportunity to be on hand when the road crews were cutting the tall trees in the forest, thereby bringing to the ground many interesting specimens of the arboreal fauna. We stayed at Chinaj? until late March, with the exception of a week spent at Toocog, another camp of the Ohio Oil Company located 15 kilometers southeast of La Libertad and on the edge of the savanna. Thus, at Toocog we were able to work both in the forest and on the savanna. In the summer of 1960, John Wellman accompanied me to El Pet?n for two weeks in June and July. Most of our time was spent at Chinaj?, but a few days were spent at Toocog and other localities in south-central El Pet?n.

Acknowledgments

I am grateful to L. C. Stuart of the University of Michigan, who made the initial arrangements for our work in El Pet?n, aided me in the identification of certain specimens, and helped in the preparation of this report. J. Knox Jones, Jr. and John Wellman were able field companions, who added greatly to the number of specimens in the collection. In Guatemala, Clark M. Shimeall and Harold Hoopman of the Ohio Oil Company of Guatemala made available to us the facilities of the company's camps at Chinaj? and Toocog. Alberto Alcain and Luis Escaler welcomed us at Chinaj? and gave us every possible assistance. Juan Monteras and Antonio Alda?a made our stay at Toocog enjoyable and profitable. During our visits to southern El Pet?n, Julio Bol?n C. worked for us as a collector, and between March and June he collected and saved many valuable specimens; his knowledge of the forest and its inhabitants was a great asset to our work. Jorge A. Ibarra, Director of the Museo Nacional de Historia Natural in Guatemala assisted us in obtaining necessary permits and extended other kindnesses. To all of these people I am indebted for the essential parts that they played in the completion of this study.

Field work in the winter of 1960 was made possible by funds from the American Heart Association for the purposes of collecting mammalian hearts. My field work in the summer of 1960 was supported by a grant from the Graduate Research Fund of the University of Kansas.

DESCRIPTION OF THE AREA

A vast lowland region stretches northward for approximately 700 kilometers from the highlands of Guatemala to the Gulf of Mexico. The northern two-thirds of this low plain is bordered on three sides by seas and forms the Yucat?n Peninsula. The lowlands at the base of the Yucat?n Peninsula make up the Departamento El Pet?n of Guatemala. The area with which this report is concerned consists of the south-central part of El Pet?n.

Physiography

Immediately south of Chinaj? is a range of hills, the Serrania de Chinaj?, having an almost due east-west axis and a crest of about 600 meters above sea level. South of the Serrania de Chinaj? are succeedingly higher ridges building up to the Meseta de Cob?n and Sierra de Pocolha and eventually to the main Guatemalan highlands. The northern face of the Serrania de Chinaj? is a fault scarp dropping abruptly from about 650 meters at the crest to about 140 meters at the base. From the base of the Serrania de Chinaj? northward to the R?o de la Pasi?n at Sayaxch? the terrain is gently rolling and has a total relief of about 50 meters. North of the R?o de la Pasi?n is a low dome reaching an elevation of 170 meters at La Libertad; see Stuart for further discussion of the physiography of central El Pet?n. The rocks in southern El Pet?n are predominately Miocene marine limestones; there are occasional pockets of Pliocene deposits. There is little evidence of subterranean solution at Chinaj?, but northward in central El Pet?n karsting is common. The upper few inches of soil is humus rich in organic matter; below this is clay.

Climate

The climate of El Pet?n is tropical with equable temperatures throughout the year. Temperatures at Chinaj? varied between a night-time low of 65? F. and a daytime high of 91? F. during the time of our visits. In the K?ppen system of classification the climate at Chinaj? and Toocog is Af. Rain falls throughout the year, but there is a noticeable dry season. To anyone who has traveled from south to north in El Pet?n and the Yucat?n Peninsula, it is obvious from the changes in vegetation that there is a decrease in rainfall from south to north. There is a noticeable difference between Chinaj? and Toocog. Although rainfall data are not available for Chinaj? and Toocog, there are records for nearby stations . At Paso Caballos on the R?o San Pedro about 40 kilometers northwest of Toocog the average annual rainfall amounts to 1620 mm.; the driest month is March , and the wettest months are June and September . At Cubilquitz, Alta Verapaz, about 35 kilometers south-southwest of Chinaj? and at an elevation of 300 meters, the average annual rainfall is 4006 mm.; the driest month is March , and the wettest months are July and October .

During the 18 days in February and March, 1960, that we kept records on the weather at Chinaj? moderate to heavy showers occurred on seven days. During our stay there in June and July rain fell every day, as it did in Toocog. However, during the week spent at Toocog in March no rain fell.

Vegetation

The vegetation of northern and central El Pet?n has been studied by Lundell , who made only passing remarks concerning the plants of the southern part of El Pet?n. No floristic studies have been made there. The following remarks are necessarily brief and are intended only to give the reader a general picture of the forest. I have included names of a few of the commoner trees that I recognized.

GAZETTEER

The localities from which specimens were obtained are cited below and shown on the accompanying map .

Chinaj?.--Lat. 16? 02?, long. 90? 13?, elev. 140 m. Camp of the Ohio Oil Company of Guatemala and formerly a small settlement. On some maps Chinaj? is located just to the north of the Alta Verapaz--El Pet?n boundary; recent surveys place the location just to the south of the imaginary line through the rainforest. Field work was conducted in the immediate vicinity of the camp, on the lower slopes of the Serrania de Chinaj?, and at several sites to the northwest and north-northwest of Chinaj?, where the forest was being cleared. The entire area supports rainforest.

La Libertad.--Lat. 16? 47?, long. 90? 07?, elev., 170 m. A town on the savannas in central El Pet?n; although we collected there in the rainy season, the specimens obtained on the savannas are not included in this report.

Paso Sub?n.--Lat. 16? 38?, long. 90? 12?, elev. 90 m. A small settlement on the R?o Sub?n, a tributary of the R?o de la Pasi?n. Specimens were obtained in rainforest in the immediate vicinity of the settlement.

R?o de la Pasi?n.--A large river flowing northward through southern El Pet?n and thence westward into the R?o Usumacinta. Specimens were obtained along the river between the R?o Sub?n and Sayaxch?.

R?o San Rom?n.--A river flowing northward in south-central El Pet?n to the R?o Salinas . We collected along the river at a place about 16 kilometers north-northwest of Chinaj?, approximately at Lat. 16? 10?, long. 90? 17?, elev. 110 m. In the dry season the river was clear; it is surrounded by rainforest.

Sayaxch?.--Lat. 16? 31?, long. 90? 09?, elev. 80 m. A town on the southern bank of the R?o de la Pasi?n. Specimens were obtained in the rainforest and in cleared areas in the immediate vicinity of the town.

Toocog .--Lat. 16? 41?, long. 90? 02?, elev. 140 m. A camp of the Ohio Oil Company of Guatemala located at the rainforest-savanna edge, 15 kilometers southeast of La Libertad. Although we collected on the savannas as well as in the forest, especially to the east of the camp, only species obtained in the forest are considered in this report.

THE HERPETOFAUNA OF THE RAINFOREST

In presenting an account of the herpetofauna of southern El Pet?n three items need to be considered: The composition of the fauna; the ecology of the fauna; the relationships of the fauna. Each of these topics is discussed briefly below. Logically a discussion of the origin of the fauna should follow, but this is being withheld for inclusion in a report on the herpetofauna of the entire El Pet?n by L. C. Stuart and the author; at that time the above topics will be expanded to cover the herpetofauna of the whole region.

Composition of the Fauna

TABLE 1.--COMPOSITION OF THE HERPETOFAUNA IN SOUTHERN EL PET?N, GUATEMALA.

A total of 78 species of amphibians and reptiles has been found in the rainforests in southern El Pet?n; a break down into families and genera is given in table 1. Another 13 species probably occur in southern El Pet?n . The fauna primarily is composed of typical humid lowland forest inhabitants, such as:

Nevertheless, the region also provides at least a limited amount of habitat suitable for some species that are more frequently found in open forest of a drier nature; such species include:

Because of the absence of sufficiently open habitat or owing to the presence of competitors, some conspicuous members of sub-humid forests are not present in southern El Pet?n. Conspicuous absentees are the following:

PLATE 7

PLATE 8

PLATE 9

PLATE 10

Ecology of the Herpetofauna

In the following discussion of the ecological distribution of amphibians and reptiles in the rainforest I have depended chiefly on my observations made in southern El Pet?n, but have taken into consideration observations made on the same species in other regions, together with reports from other workers. The reader should keep in mind that the evidence varies from species to species. Of some species I have observed only one animal in the field; of others, I have seen scores and sometimes hundreds of individuals. For species on which I have few observations or rather inconclusive evidence, the circumstance of inadequate data is mentioned.

In analyzing the ecological distribution within the forest, it is convenient to recognize five subdivisions ; each is treated below as a unit.

Relationships of the Fauna

In determining a measure of faunal resemblance, I have departed from the formulae discussed by Simpson and have analyzed the degree of resemblance by the following formula used to calculate an index of faunal relationships:

The herpetofauna of southern El Pet?n has been compared with that in the Tikal-Uaxact?n area , that in the humid lowlands of Alta Verapaz , and that in the Mexican state of Yucat?n . The herpetofaunas of lowland Alta Verapaz and Yucat?n are the largest, having respectively 94 and 91 species, where as there are 78 species known from southern El Pet?n and 64 from the Tikal-Uaxact?n area. An analysis of faunal relationships shows that the faunas of the rainforests of southern El Pet?n and lowland Alta Verapaz are closely related. The relationships between these two areas and the Tikal-Uaxact?n area in northern El Pet?n is notably less. Apparently the biggest faunal changes take place between southern El Pet?n and the Tikal-Uaxact?n area, and between the latter and Yucat?n. As stated by Stuart the Tikal-Uaxact?n is transitional between the humid rainforests to the south and the dry outer end of the Yucat?n Peninsula. The transitional nature of the environment is exemplified by a rather depauperate herpetofauna consisting of some species of both dry and humid environments and lacking a large fauna typical of either. Contrariwise, the continuity of the environment from southern El Pet?n to the lowlands of Alta Verapaz is reflected in degree of resemblance of the herpetofaunas.

TABLE 2.--INDEX OF FAUNAL RELATIONSHIPS BETWEEN SOUTHERN EL PET?N AND OTHER REGIONS.

Most of the species of amphibians and reptiles found in southern El Pet?n are found in humid tropical forests from the Isthmus of Tehuantepec southeastward on the Atlantic lowlands well into Central America.

ACCOUNTS OF SPECIES

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