In presenting an account of the herpetofauna of southern El Petén three items need to be considered: (1) The composition of the fauna; (2) the ecology of the fauna; (3) 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 Petén 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 Petén, Guatemala.
| Group | Families | Genera | Species |
| Gymnophiona | (1)[A] | (1) | (1) |
| Caudata | 1 | 1 | 2 |
| Salientia | 6 | 10 (1) | 19 (1) |
| Crocodilia | 1 | 1 | 1 |
| Testudines | 4 | 7 | 8 |
| Sauria | 6 | 13 (1) | 19 (1) |
| Serpentes | 4 | 21 (7) | 29 (10) |
| Total | 22 (1) | 53 (10) | 78 (13) |
[A] Numbers in parenthesis indicate the number of additional taxa that probably occur.
A total of 78 species of amphibians and reptiles has been found in the rainforests in southern El Petén; a break down into families and genera is given in table 1. Another 13 species probably occur in southern El Petén (see Hypothetical List of Species). The fauna primarily is composed of typical humid lowland forest inhabitants, such as:
| Hyla ebraccata | Eumeces sumichrasti |
| Hyla loquax | Ameiva festiva edwardsi |
| Phyllomedusa callidryas taylori | Imantodes cenchoa leucomelas |
| Smilisca phaeota cyanosticta | Leptophis ahaetulla praestans |
| Anolis biporcatus | Xenodon rabdocephalus mexicanus |
| Anolis capito | Bothrops nasutus |
| Anolis humilis uniformis | Bothrops schlegeli schlegeli |
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:
| Hyla microcephala martini | Anolis sericeus sericeus |
| Hyla staufferi | Eumeces schwartzei |
| Hypopachus cuneus nigroreticulatus | Oxybelis aeneus aeneus |