. The biogeography of the herpetofauna of the subhumid forests of Middle America : (Isthmus of Tehuantepec to northwestern Costa Rica). Herpetology; Reptiles, Fossil. America in areas some of which are now covered by humid forests. Furthermore, the outer portion of the Yucatan Peninsula did not become continuously land-pos- itive until the middle to late Pleistocene (for a discussion of sea-level changes in late Tertiary and Quaternary, see Haffer, 1987:9). The subsequent discussion is predicated on this scenario and, thus, some of our comments will be at variance with some of those expressed
. The biogeography of the herpetofauna of the subhumid forests of Middle America : (Isthmus of Tehuantepec to northwestern Costa Rica). Herpetology; Reptiles, Fossil. America in areas some of which are now covered by humid forests. Furthermore, the outer portion of the Yucatan Peninsula did not become continuously land-pos- itive until the middle to late Pleistocene (for a discussion of sea-level changes in late Tertiary and Quaternary, see Haffer, 1987:9). The subsequent discussion is predicated on this scenario and, thus, some of our comments will be at variance with some of those expressed in various sys- tematic studies of given taxa. Some of these differences in interpretation will be discussed where pertinent. ANALYSIS OF GENERALIZED TRACKS AND AREAS OF ENDEMISM Savage (1983) has discussed the difficulities of general- ized track analysis and set forth some principles for estab- lishing generalized tracks. We plotted the total distribution of each of the 96 Subhumid Assemblage species. We also plotted the total distribution for closely related species of each of the 96 species when those relationships are known. Based upon a review of these distributions and following the principles set forth by Savage (1983), we were able to identify five generalized tracks for our Subhumid Assemblage species (Table 10). Three major areas of endemism occur within the subhumid areas under consid- eration (see Fig. 16 in Savage, 1983). These are the outer Yucatan Peninsula (21 endemic species), the Pacific low- lands from southeastern Guatemala to northwestern Costa Rica (14 endemics), and the Pacific lowlands of the Isthmus of Tehuantepec (9 endemics). The phylogenetic relationships of the endemic species found in the subhu- mid forests of Middle America are important in expressing historical relationships among the subhumid areas that are presently separated from each other by more mesic condi- tions than those that prevailed in the past. Savage (1983) has provided a discussi
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