Great Basin Naturalist Volume 41 Number 1 Article 5 3-31-1981 A new Hypsiglena from Tiburon island, Sonora, Mexico Wilmer W. Tanner Brigham Young University Follow this and additional works at: https://scholarsarchive.byu.edu/gbn Recommended Citation Tanner, Wilmer W. (1981) "A new Hypsiglena from Tiburon island, Sonora, Mexico," Great Basin Naturalist: Vol. 41 : No. 1 , Article 5. Available at: https://scholarsarchive.byu.edu/gbn/vol41/iss1/5 This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Great Basin Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. A NEW HYPSIGLENA FROM TIBURON ISLAND, SONORA, MEXICO Wilmer W. Tanner' Abstract.— Hypsiglena torquata tiburonensis is described as new to science from Isla del Tiburon, Sonora, Mexi- co. Notes pertaining to other taxa in the genus are inchided. The islands in the Gulf of California con- tern is similar to deserticola, but in the para- tinue to produce interesting variations in the type it is as in northern Sonora and Arizona genus Hypsiglena. Few islands are without specimens. The subspecies tiburonensis is representatives of the genus and all island most closely related to those nearby popu- populations show some variations not found lations in Sonora and Arizona and in the in Baja California or Sonora populations. Great Basin, but it is distinct in the number, Those islands furthest from the coast and off size, and shape of the dorsal spots. the coastal shelf, such as Tortuga and Santa Description.— Rostral broad, rounded, Catalina, show the most variation, an in- and projecting anteriorly 0.7 mm, 17.5 per- dication of their longer isolation. cent of distance to anterior edge of frontal; A most unusual pair of specimens is avail- loreals 1-1; preoculars 2-2; temporals 1-2; able from the island of Tiburon. They are un- supralabials 8-8; infralabials 10-10, four rows usual in their color pattern and particularly of gulars between posterior chinshields and in the large number of dorsal spots. As noted first ventral; ventrals 185; caudals 52; anal di- above, it is not unexpected for island popu- vided; dorsal scales in 21-21-15 longitudinal lations to be differentiated from the mainland rows. populations, but, considering the short dis- Nape pattern of three dark blotches, the tance from costal Sonora to Tiburon, one median one of these with three parts, the an- would not expect such a radical departure in terior median portion narrow, extending pattern. Because the population is distinct, I from the parietal posteriorly 5 scales to fuse choose to name it— on each side with the lateral portions of this spot; lateral nape spots separated from me- dian and extending anteriorly to orbit; dorsal Hypsiglena torquata tiburonensis, n. subsp. blotches on body 86, many divided or nar- Fig. 1 rowly connected medially, spots separated by HoLOTYPE.- An adult female, BYU 33181, narrow pale cross-bands usually one-half taken by James R. Dixon, on Isla del Tiburon, scale wide, dorsal spots when united forming Sonora, Mexico, 14 August 1974. a band across dorsum involving 7-9 scale Paratype.- An adult female, MVZ 37802, rows. Dorsum of head without dark spots; taken by C. G. Sibley at Ensenada del Perro, body color a light brown with narrow, Isla del Tiburon, 10 November 1941. cream-colored mottling separating the spots. Diagnosis.— A subspecies of Hypsiglena Measurements.— Snout-vent length 376 torquata characterized by light brown spots, mm; tail length 68 mm; tail 15.3 percent of which are narrowly separated from one an- total length; head length, from snout to pos- other (usually less than one scale) and in- terior edge of parietals 11.4 mm; head width volving 7-9 dorsal scale rows. There is a 10.5 mm; diameter of eye 2.1 mm. strong tendency for the dorsal spots to be Remarks.— The size, shape, and number of separated or only narrowly connected at the dorsal body spots is the most distinctive char- dorsal midline. In the holotype, the nape pat- acter in tiburonensis. There are other sub- 'Life Science Museum, Brigham Young University, Provo, Utah 84602. 139 140 Great Basin Naturalist Vol. 41, No. 1 species with dorsal spots that extend across [1946]). Although the nape pattern is similar to that of deserticola, it does its the dorsum to occupy 7-9 rows of scales {t. have own uniqueness and appears to consist basically of torquata, t. nuchulata, t. baueri), and perhaps occasional specimens in other subspecies, but three narrowly fused spots. series in these the spots are longer; that is, they in- A of 10 females from Sonora pro- volve 2-3 or more scale lengths. In tibiiro- vides little scutellation variation between nensis the dorsal spots are less than 2 scales them and tiburonensis, with ventral means and usually 1^/2. The pale bands between the 183.3 to 182.5, respectively. The caudals are dorsal spots are narrow, less than one scale also close, with means of 55 to 52, respective- length; thus, the narrow spots and interspaces ly (the paratype is missing its tail tip). The provide space for more spots, characteristic greatest variation between Sonora and Tibe- ron specimens occur in the of dorsal of this subspecies. In t. venusta there are number large numbers of dorsal spots (69-95); how- body spots, with females having 59.1 to 77.5, ever, they are small, divided middorsally to respectively. form two rows that extend for most or all the It should be noted again that the series body length and involve only 2-3 rows of from Sonora includes both those specimens scales. Furthermore, they are, as in tihuro- showing a pale nape band (typical torquata), nensis, narrowly divided by lighter cross- and those representing the northern type bands between the spots (Tanner 1944 (ochrorhynchus), all of which are without any B Fig. 1. Hypsiglena torquata tortugaensis, BYU 33181, holotype: A, head and nape patterns; B, dorsal spots. March 1981 Tanner: A New Hypsiglena 141 remnant of the white band. In the torquata California. It is in Sonora that the light, dorsal body pattern, the pale areas that di- cream-colored nape band disappears and the vide the dark dorsal spots are narrow, as in dark nape pattern becomes an irregular band tiburonensis, but otherwise the pattern is or three nape spots. An occasional specimen very different with fewer, larger, and broader from southeastern Sonora and adjoining spots. In the specimens from northern Sonora southwestern Chihuahua has a much broader, and most of adjoining Arizona, northwestern more uniform dark band. Chihuahua, and extreme south-central Utah, It was from this general area and on the the light areas between the spots are wider, basis of comparisons with more southern covering one or more scales. The nape pat- populations that Dunn (1936) synonomised tern in the northern populations is usually a ochrorhyncha with torquata, this in spite of fusion of the spots to form an irregular dark the very few specimens available and in con- brown band that laterally extends anteriorly trast to the Stejneger and Barbour (1917) as- to the orbits; or the nape pattern may have a signment. Both Tanner (1946) and Dixon central elongate spot extending posteriorly (1965 and 1967) accepted ochrorhyncha from the parietals for approximately 7-10 based on the distinct color pattern of limited scales and, at its widest, 3-4 scales wide. In specimens available between typical speci- some specimens the median spot is fused on mens of the two types. With a substantial in- one side with a lateral nape spot. In all speci- crease in the numbers of specimens through- mens examined, the lateral spots extend to out the entire range of Hypsiglena, it is now the orbit. generally agreed that only one widespread Based on color pattern, the relationship of species (torquata) is assignable to the genus tiburonensis is closer to those populations in Hypsiglena (Tanner 1954, 1958, 1960, 1962, northwestern Sonora and those further to the 1963, 1960, 1966, Schmidt 1953, Bogert and north, including deserticoki (which has a sim- Oliver 1945, Zweifel and Norris 1955, Smith ilar nape pattern). There is also a general and VanCelder 1955, Duellman 1957, Fugler lightening of the brown color and a strong and Dixon 1961, Fouquette and Rossman tendency for scales in the dorsal blotches to 1963, Hardy and McDiarmid 1969). be edged with dark, its centers being a light- Dixon and Lieb (1972) described as a new er brown. This lightening seems to be true species Hypsiglena tanzeri. Based on the de- for desert populations, but a darker brown is scription, figures, and my examination of the present in most areas where an increase of paratype (LACM 72068), it appears to be a moisture occurs. Three specimens from San color variation of torquata and should thus be Esteban Island (CAS-SU-9038, UM 128641, considered a unique subspecies of torquata. and MVZ 74953) are similar to tiburonensis An examination of t. tanzeri places it as one in having numerous dorsal body spots, 90, 78, color pattern extreme in the large size and and 82, respectively. Other characters are small number of body spots; t. venusta is the also similar, such as ventrals, ? 184-186, and other extreme. In Hypsiglena, the size, shape, caudals, 46-52; one male has 173 ventrals and number (now known to range from and 55 caudals. The similarities between 37-95) of body spots and the nape pattern these two island populations dictate that they are highly variable.