Greater Short-horned Lizard (Phrynosoma hernandesi)

Photo by Jim Rorabaugh

Greater Short-horned Lizard, Rancho Los Fresnos, Sonora. Photo by Jim Rorabaugh.

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Description

The Greater Short-horned Lizard (Phrynosoma hernandesi) is a moderate-sized (< 114 mm SVL) lizard with a typical Phrynosoma flat, wide body, and a tail of moderate length.  It has a relatively broad head for a horned lizard, the back of which is armed with short horns separated by a deep and relatively wide notch in which the notch between the occipital (central) horns is wider than the length of either horn.  The two occipital horns are very short and do not extend back as far as the temporal horns on each side.  The ventral scales are smooth and sharply pointed at the rear.  One row of enlarged fringed scales lies at the margin of the abdomen and dorsum.

The dorsal background color is highly variable, from brown, gray, yellow to red, often overlain with dark blotches or crossbars.  A mid-dorsal light and diffuse stripe is present in some specimens.  A dark blotch is usually present on either side of the neck. The venter is mottled with gray and white; the chin and throat may be yellow, reddish or orange in males. New born lizards resemble adults except that their colors are muted and they are 20-32 mm SVL.  Males have enlarged postanal scales, and in comparison to the females, have a wider tail base and more prominent femoral pores.  The largest lizards are females.  Lahti (2010) reported on a population of dwarf Greater Short-horned Lizards (< 84.5 mm SVL) from the San Luis Valley, Colorado.

In the 100-Mile Circle, the Greater Short-horned Lizard is most likely to be confused with the Rock Horned Lizard (Phrynosoma ditmarsi).  That species has keeled ventral scales, a broad head, especially at the rear of the jaw, much reduced occipital horns that form rounded, flaring extensions on both sides of the head separated by a deep and narrow notch, and a high post-orbital ridge, roughly parallel to the margin of the occipital horns.  In the Circle, the Rock Horned Lizard is only known from the Sierra Manzanal south of Cananea, although it may have been overlooked in other sky islands in Sonora.  The Regal Horned Lizard (Phrynosoma solare) is found generally at lower elevations and has four large occipital horns, the bases of which are all in contact. The Texas Horned Lizard and Round-tailed Horned Lizard have two and no rows of fringed scales at the margin of the abdomen and dorsum, respectively.

This taxon was long considered a subspecies of the P. douglassi, and the older literature uses that nameZamudio et al. (1997) recognized Phrynosoma hernandesi as a species distinct from P. douglassi, which is now restricted to portions of the Pacific Northwest. Two subspecies of P. hernandesi are recognized.  Only P. h. hernandesi occurs in our area.

The Greater Short-horned Lizard is a species of high valleys and mountains, primarily in the eastern half of the 100-Mile Circle.  It occurs in most mountain ranges from the Pajarito-Atascosa complex east to the Chiricahuas, Pinaleños, and Santa Teresas but is not known from the Sierrita or Dragoon mountains.  The species occurs north to the Pinal, Sierra Ancha, Superstition, and Mazatzal mountains. It also occurs in the Sonoita, San Rafael, Sulphur Springs, and San Bernardino valleys. In the Sonora portion of the Circle, it is known from the Sierras Las Avispas (WSW of Nogales), Azul, Mariquita, Los Ajos, and San Jose, Cananea and vicinity, grasslands to the east of Cananea, and Rancho Los Fresnos immediately south of the San Rafael Valley in Arizona.  It has been documented at elevations of 1190-2881 m, although outside the Circle it has been found as high as 3424 m (in New Mexico, Degenhardt et al. 1996).  In the Circle this species occurs from semi-desert and Plains grasslands upslope through oak and pine-oak woodland, and mixed conifer forest.  It likely occurs in spruce-fir forest, as well.  This lizard is locally abundant in areas of fine sand or loose soil. Throughout its range, the Greater Short-horned Lizard occurs from the Rocky Mountain region of extreme southern Canada, Montana, and Wyoming south to Arizona, New Mexico, and Texas, as well as the Mexican states of Sonora, Chihuahua, and Durango.

Records in the University of Arizona collection date from 1 March to 13 November within the Circle, but few lizards are observed or collected in March and November. This is a diurnal lizard, often active through the day at higher elevations. It can be found active during surprisingly cold temperatures.  Montanucci and Baur (1982) described courtship and mating, which occurs from March through May.  Five to 48 young are born alive after about three months of gestation (Goldberg 1971, Howard 1974, Parker and Pianka 1975, Lahti 2010). Neonates in Arizona and northern Sonora are born in July and August (Goldberg 1971, Howard 1975).  Litter size is typically less in northern populations of this species.  In Arizona, litter size was 9-30 (mean = 16.7, Goldberg 1971).  Females and males mature at 63 and 59 mm SVL, respectively (Howard 1974).

The Greater Short-horned Lizard eats primarily ants (49-99% by frequency), but also beetles, and to a lesser degree other insects, pebbles, and organic debris (Parker and Pianka 1975, Lahti 2010).  Larger lizards consume more beetles, and smaller horned lizards consume relatively small species of ants.  Despite the preponderance of ants in the diet, Lahti and Beck (2007) did not consider this species an ant specialist.  Generally, the clade of montane horned lizards with shorter horns that includes P. hernandesi, douglassi, orbiculare, and ditmarsi consume fewer ants by frequency than long-horned horned lizards (Pianka and Parker 1975).  When confronted by a predator, the Greater Short-horned Lizard is known to squirt blood from the orbital sinuses around the eyes, but it does so infrequently.

With a valid Arizona hunting license, four Greater Short-horned Lizards can be collected per year or held in possession, alive or dead, although collection is prohibited in protected areas such as National Park Service units without special permits.  It is a species of least concern on the 2014 IUCN Red List.  In the 100-Mile Circle, the forested montane habitats of this lizard are vulnerable to the effects of climate change and wildfire.  Most of the higher mountain ranges in southeastern Arizona where this species occurs have experienced extensive stand-replacing wildfires in the last three decades, although the effects of these fires on the Greater Short-horned Lizard have not been studied.

Suggested Reading:

Brennan, T.C., and A.T. Holycross. 2006. Amphibians and Reptiles in Arizona. Arizona Game and Fish Department, Phoenix, AZ.

Degenhardt, W.G., C.W. Painter, and A.H. Price. 1996.  Amphibians and Reptiles of New Mexico. University of New Mexico Press, Albuquerque.

Goldberg, S.R. 1971. Reproduction in the Short-horned Lizard, Phrynosoma douglassi in Arizona. Herpetologica 27:311-314.

Howard, C. W. 1974. Comparative reproductive ecology of horned lizards (genus Phrynosoma) in the southwestern United States and northern Mexico. Journal of the Arizona Academy of Science 9:108-116.

Lahti, M.E. 2010. The status of dwarfed populations of Short-horned Lizards (Phrynosoma hernandesi) and Great Plains Toads (Anaxyrus cognatus) in the San Luis Valley, Colorado. Dissertation, Utah State University, Logan.

Lahti, M.E., and D.D. Beck. 2007. Ecology and ontogenetic variation of diet in the Pigmy Short-horned Lizard (Phrynosoma douglasii). American Midland Naturalist 159:327-339.

Montanucci, R.R., and B.E. Baur. 1982. Mating and courtship behaviors of the Short-horned Lizard, Phrynosoma douglassi. Copeia 1982 (4):971-974.

Parker, W.S., and E.R. Pianka. 1975. Ecology of horned lizards: a review with special reference to Phrynosoma platyrhinos. Copeia 1975 (1):141-162.

Sherbroke, W.C. 2003. Introduction to Horned Lizards of North America. University of California Press, Berkeley.

Zamudio, K.R., K.B. Jones, and R.H. Ward. 1997. Molecular systematics of short-horned lizards: biogeography and taxonomy of a widespread species complex. Systematic Biology 46:284-305.

Author: Jim Rorabaugh

For additional information on this species, please see the following volume and pages in the Sonoran Herpetologist: 2004 Jun:58-61.

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