In Michoacán this species is confined to elevations of less than 1000 meters on the coast and foothills of the Sierra de Coalcomán. In this region in the months of June and July, breeding congregations have been found in temporary pools and along streams.
Smith and Taylor (1948:39), in their key to the Mexican species of Bufo, placed emphasis on the nature of the supraorbital and postorbital crests (whether they form a curve or a sharp angle) in distinguishing Bufo marmoreus from Bufo perplexus. In the original description of perplexus, Taylor (1943a:347) characterized the species as follows: supraorbital and postorbital crests forming a sharp angle, instead of a curve as in marmoreus; supratympanic crest smaller than in marmoreus; diagonal lateral stripe lacking in females; concentration of dorsal tubercles as found in marmoreus lacking in males. The discovery of specimens in which the crests form a curve and others in which the crests form an angle in both the Tepalcatepec Valley and in the coastal lowlands prompted an investigation of these characters and others throughout the ranges of the species. An examination of 410 specimens has resulted in the following conclusions.
Table 1.—Variation in the Shape of the Supraorbital and Postorbital Cranial Crests in Bufo marmoreus and B. perplexus.
| Locality | N | Curved | Intermediate | Angular |
| Tepalcatepec Valley | 50 | 10 (20.0%) | 17 (34.0%) | 23 (46.0%) |
| Morelos | 12 | 2 (16.6%) | 5 (41.7%) | 5 (41.7%) |
| Izúcar, Puebla | 4 | 2 (50.0%) | 0 (0.0%) | 2 (50.0%) |
| Southern Sinaloa | 1 | 1(100.0%) | 0 (0.0%) | 0 (0.0%) |
| Puerto Vallarta, Jalisco | 2 | 2(100.0%) | 0 (0.0%) | 0 (0.0%) |
| Colima | 45 | 25 (55.0%) | 18 (40.0%) | 2 (5.0%) |
| Coast of Michoacán | 55 | 35 (63.6%) | 17 (30.9%) | 3 (5.5%) |
| Acapulco, Guerrero | 7 | 7(100.0%) | 0 (0.0%) | 0 (0.0%) |
| Chilpancingo, Guerrero | 10 | 1 (10.0%) | 4 (40.0%) | 5 (50.0%) |
| Pochutla, Oaxaca | 13 | 6 (46.2%) | 6 (46.2%) | 1 (7.6%) |
| Tehuantepec, Oaxaca | 177 | 81 (45.8%) | 67 (37.8%) | 29 (16.4%) |
| Tonolá, Chiapas | 1 | 0 (0.0%) | 0 (0.0%) | 1(100.0%) |
| Veracruz | 33 | 26 (78.8%) | 6 (18.2%) | 1 (3.0%) |
| Total | 410 | 198 (48.3%) | 140 (34.2%) | 72 (17.5%) |
1. Although the highest percentage of individuals having the supraorbital and postorbital crests forming a sharp angle is from localities in the Balsas-Tepalcatepec Basin, numerous individuals from throughout the range of marmoreus have the crests forming an angle (Table 1).
2. In all samples of ten or more specimens, some toads have the supraorbital and postorbital crests forming a sharp angle, some have the crests forming a curve, and some have an intermediate condition.
3. The relative size of the supratympanic crest is highly variable in all samples examined.
Fig. 3. Adult male of Bufo perplexus from Apatzingán, Michoacán. × 1.5.