An Aberrant Pattern Morph in a Western Diamondback Rattlesnake, Crotalus atrox, from Southern Texas

Abstract

Aberrant patterns have been reported for several North American crotaline species (Gloyd, 1935 and 1958; Klauber, 1972; Livezey, 1949; and Nickerson and Mays, 1968). Herein, I report another pattern aberration in an adult male Crotalus atrc)x (Texas A & I Collections, TAIC-1423) from Texas. The snake was collected by a Mr. Ammons, on the Laureles Division of the King Ranch, Nueces Co., in September 1968. This specimen is unusual in that the typical rhombic or diamond-shaped blotches are absent? as are the black and white alternating tail bands (Fig. 1). The pattern instead consists of a pair of dark brown paravertebral stripes beginning immediately posterior to the head. The stripes are two to three dorsal scale rows wide and are separated by a mid-dorsal light stripe two to three scale rows wide. The paravertebral stripes remain separate to the level of the 79th ventral. At this area the dark stripes merge, terminating the light mid-dorsal stripe. The dark color is slightly diffuse at the merger, but nevertheless discernible? and occupies five mid-dorsal scale rows at the 89th ventral. It continues to approximately the 129th ventral, where it fades into the light brown color of the lateral and posterior dorsal surfaces. The ventral pattern is not atypical. The tail is mostly black-brown on the dorsal and lateral surfaces with occasional single scales having diffuse white areas sprinkled with black. The subcaudal scales are mottied with black and white. The light-bordered ocular stripe is absent. Gloyd (1958) described three Crotulus cltrox from southern Texas with similar color aberrations. Mensural and meristic data of these three specimens and TAIC-1423 are compared (Table 1) with the mean values for C. atrox presented by Klauber (1972). The meristics of scutellation for all aberrant specimens are within the limits of normal variation for the species (Klauber, 1972: Table 2:7). The four anomalous specimens are from localities within 250 km of each other in south Texas. Anomalous paravertebral striping is evidently not deleterious to survival! as many of the reported specimens are adults, including TAIC-1423, with a total length of 1169 mm and fully ossified hemipenal spines. The ground