Clark’s Spiny Lizard (Sceloporus clarkii)
Clark's Spiny Lizard. ©2013 Dancing Snake Nature Photography
Clark's Spiny Lizards (male [lower), female), Northern Jaguar Reserve, Sonora, MX. Photo by Jim Rorabaugh
Clark's Spiny Lizard and Horse Lubber, Marijilda Cyn, Graham Co., AZ. Photo by Jim Rorabaugh
Clark's Spiny Lizard. ©2013 Dancing Snake Nature Photography
Clark's Spiny Lizard, southern Sonora. Photo by Jim Rorabaugh.
Adult male Clark's Spiny Lizard, Marijilda Cyn, AZ. Photo by Jim Rorabaugh.
This magnificent arboreal lizard is frequently observed in riparian woodlands within the hundred mile circle (centered on Tucson). Look for these large, rough-scaled lizards in the cool of the morning, as rays of sunlight first strike the tree trunks. They often bask, oriented head-downward, searching for insects at a height of 1-2 meters on ash, sycamores, cottonwoods, walnuts, oaks, and other large trees. Later, as temperatures rise, they often ascend into the canopy where they have been observed on branches as high as 40 m. (Balinger in Degenhardt et al. 1996). In some areas, such as the Pinaleño Mts., they also live on massive boulders (Lowe 1964; Nickerson and Mays 1970).
At their study area near Sunflower, Maricopa Co., Arizona, Tinkle and Dunham (1986) found the species to be active from April to October. Females attained sexual maturity at 22 months and a snout-vent length of 89 mm. They produced only one clutch per year (average 20 eggs), which was deposited in June. Population densities fluctuated widely among years, with an overall average of 25 lizards per hectare. Experiments involving the removal of Sceloporus clarkii and Urosaurus ornatus from sections of the study area did not appear to significantly impact the ecology of Sceloporus undulatus, thus failing to demonstrate direct competition between the three species of lizards (Tinkle 1982).
The available data on stomach contents (summary in Degenhardt et al. 1996) indicate a broad diet including beetles, ants, wasps, butterflies, moths, spiders, and grasshoppers. They also occasionally ingest Urosaurus ornatus (Tinkle and Dunham 1986). Bezy and Enderson (2003) document attempted predation by the Sonoran Whipsnake (Masticophis bilineatus), and Holycross et al. (2002) found S. clarkii among the stomach contents of Crotalus lepidus.
Clark Spiny Lizard reaches a maximum snout-vent length 125 mm (Stebbins 1985). The presence of distinct cross bands on the forelimbs is a useful feature for distinguishing the species from the Desert Spiny Lizard (Sceloporus magister), a vaguely similar animal that is quite abundant in our region. Analyses of DNA sequences indicate that the nearest relative of S. clarkii is S. melanorhinus (Wiens and Reeder 1997) found along the Pacific slopes of southern Mexico, providing additional evidence of the tropical affinities of our herpetofauna.
In Arizona, Sceloporus clarkii has a distribution somewhat similar to Masticophis bilineatus (Camper 1996) and Crotalus molossus (Lowe et al. 1986), extending from the Madrean Archipelago (“Sky Islands”) north to the Blue River, and northwest through the sub-Mogollon peninsular ranges to the Aquarius (pers. obs.) and Cottonwood Mts. (UAZ 20191), Mohave Co., and probably beyond. In southern Arizona, isolated populations occur in the Tucson, Martina, Quinlan-Boboquivari, Ajo, and Puerto Blanco Mts. (Bezy and Enderson 2003; Lowe 1964; Stebbins 1985).
The overall species range extends from the state of Jalisco north along the Pacific slope of Mexico to Sonora, Chihuahua, New Mexico, and Arizona (Sites et al. 1992). The subspecies Sceloporus clarkii boulengeri occupies the southern part of the range, north to southern Sonora (Bogert and Oliver 1945; Smith 1939; Smith and Taylor 1950) and has been observed on the trunks of coconut palms along the coast and on trees in the once vast Sinaloan Thornscrub (Hardy and McDiarmid 1969). To the north, S. c. clarkii occurs over much of Sonora (except for the Gran Desierto region), including Islas San Pedro Nolasco and Tiburon (Grismer 2002), extending across the Sierra Madre Occidental into western Chihuahua, and northward to southwestern New Mexico (west of the Rio Grande) and northwestern Arizona. Lizards found on boulders at Granite Dells, north of Prescott, Yavapai Co., Arizona, were described as S. c. vallaris based on the retention of the juvenile color pattern by large adults (Shannon and Urbano 1954). A thorough range-wide analysis of geographic variation is needed to evaluate the taxonomic status and distribution of the described subspecies. The species was named by Baird and Girard (1852) for John H. Clark who contributed specimens to the Mexican boundary survey (Degenhardt et al. 1996). Crother (“2000” ) lists the species as Clark’s Spiny Lizard (Sceloporus clarkii) and the subspecies in our area as the Sonoran Spiny Lizard (Sceloporus c. clarkii).
I thank George Bradley for information and access to specimens in the Herpetology Collection of the University of Arizona (UAZ), Peter Holm for discussion, Kit Bezy for illustration, and Kathryn Bolles for review of the manuscript.
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Author: Robert L. Bezy
Originally published in the Sonoran Herpetologist “Herpetofauna of the 100-mile Circle” 15 (02) 2003