systematics of snakes of the dipsas oreas complex - BioOne

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106 Bulletin Museum of Comparative Zoology, Vol. 158, No. 3 Figure 19. Variation in color pattern of adult female Dipsas oreas (Cope) from the Río Zaña Study Site (Cajamarca department, Peru). Top: ANSP 31777 (548 mm SVL). Bottom: ANSP 31784 (551 mm SVL). pression of the contrast according to size is more variable. However, without larger samples and ontogenetic data on pattern changes, it is not possible to make definitive statements regarding sex or size differences in color pattern. It is also unclear whether the intrapopulational variation in color pattern at the Río Zaña Study Site applies to other populations. Sample sizes for different ontogenetic stages and sexes from single localities are insufficient to disentangle these effects from geographic or random variation patterns. Nonetheless, no examples of specimens with extremely pale bands or relatively unicolor dorsums are available from localities other than the Río Zaña Study Site. Color and Pattern in Preservative. Preserved specimens retain the major pattern elements of live specimens, but colors become duller. Even specimens well over a century old (e.g., the holotype and BMNH 60.6.16.56; Fig. 14) have dark brown bands on a gray or grayish brown ground color. The lightening of the middle of the dark bands may become less evident in preservation, but most larger specimens retain even this sometimes subtle pattern characteristic. Most specimens of Dipsas oreas have a pair of elongate oval blotches on top of the head from the level of the eyes to the nape (Fig. 20). These are more or less discrete, depending on how much additional black pigment occurs atop the head. Within the Río Zaña population, there is variation in the prominence of the blotches, just as in overall dorsal pattern (Fig. 20). Nonetheless, the characteristic form and presence of these cephalic blotches is a useful identifying characteristic for D. oreas. The lateral surface of the head is usually heavily and irregularly flecked with dark pigment, often concentrated along scale sutures and sometimes forming a more or less discrete diagonal postocular bar (Fig. 21). Two specimens from unknown localities in western Ecuador, BMNH 60.6.16.56 and 60.6.16.63, have atypical head markings (Fig. 22). These lack distinct blotches on the parietals, although a pair of irregular blotches is evident on BMNH 60.6.16.56 that is similar to those on MUSM 16750 (Fig. 16). Instead, the top of the head is whitish but heavily marked with dark brown, resulting in a generally
Dipsas oreas Complex in Ecuador and Peru • Cadle 107 Figure 20. Variation in dorsal head patterns of Dipsas oreas (Cope) from the Río Zaña Study Site (Cajamarca department, Peru). Top: left, ANSP 31778 (male); right, ANSP 31786 (male). Bottom: left, ANSP 31779 (male); right, ANSP 31777 (female). The dark oval blotches centered on the parietal region are characteristic of most specimens of D. oreas, but vary within this population from very distinct to indistinct. In specimens that have very indistinct blotches (bottom right), at least the medial edges of the blotches are discernible by a dusky undulating border. Figure 21. Dipsas oreas (Cope). Lateral view of the head of a specimen from the Río Zaña Study Site (Cajamarca department, Peru), ANSP 31785. dark brown impression except under close inspection. The parietal scales of these specimens are irregularly marked with dark brown, which blends into the dark markings anteriorly and posteriorly on head. A few suture lines of the supra- and infralabials are marked with dark brown, especially anteriorly and posteriorly, but labial scales are rather unmarked compared with other specimens of Dispas oreas. Apart from the head patterns, the color patterns and other characters of BMNH 60.6.16.56 and 60.6.16.63 are typical of those seen in other specimens of D. oreas (Fig. 14). In a series of three specimens of Dipsas oreas from Chimborazo Province, Ecuador (ANSP 18117, 18120, 18123; adult female, juvenile female, and juvenile male, respectively), two show an obscure dorsal head cap without distinct parietal blotches, whereas the other (ANSP 18120; Cadle and Myers, 2003: fig. 11) has the parietal pattern typical of most D. oreas. In small juveniles, the parietal markings also tend to be more diffuse than in adults (Fig. 17 and above description of the coloration of hatchlings). The venter of Dipsas oreas is usually moderately to heavily marked with large squarish spots or blotches, usually displaced toward the outer edges of the ventrals and sometimes aligned so as to form longitudinal arrays (Fig. 14). A few speci-
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systematics of snakes of the dipsas oreas complex - BioOne

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