Phrynosoma solareRegal Horned Lizard

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Geographic Range

Phrynosoma solare is restricted to the Sonoran desert in

south-central Arizona, east to extreme southwestern New Mexico, south through most of Sonora (including Isla Tiburon) and into northern Sinaloa, Mexico (Hodges 1998).

Habitat

The Regal Horned Lizard prefers hot, dry, sandy environments.

Physical Description

The Regal Horned lizard is characterized by one row of lateral abdominal fringe scales upon a wide, flattened, toad-like body. The tail is short and broad at the base. Four large occipital horns at the base of the head continuous with six temporal horns, form a large crown of ten sharp, pointed horns along the base of the head. Another distinguishing characteristic of the horned lizard is that the ventral portion of its body is composed of rows of keeled scales. The squat form, head armor, and dragon-like appearance has given rise to the name "hornytoad", "horned toad", and "horned lizard", which is the nickname commonly used for this particular genus. The Horned lizard is typically soft desert gray along the back and head. It is composed of pastel shades of tan, brown, red, and yellow. The underparts are pale, yellowish gray. Color change occurs within minutes, changing from light to dark or vice versa depending on the environment. Phrynosoma solare are on average about 5 inches in length (Seymour and Royo 1999).

Reproduction

Mating for the Regal Horned lizard begins in late April, peaks in June, and stops abruptly in July. Egg laying starts a few weeks later, usually in late July and early August. The eggs are laid in the sand where they require several weeks for further development before the eggs hatch. The egg shells are white and flexible and average about one-half inch in diameter. The number of eggs varies anywhere from 10-30 eggs, with an average of about 15. The young are called hatchlings. They are about 7/8 to 1-1/8 inches long, snout to vent (Seymour and Royo 1998). The hatchlings receive no parental care upon hatching and immediately bury themselves in the sand. They are now responsible for finding and hunting for their own food. There is no evidence that the young reproduce within their first year, but they are classified as young adults by the end of the second summer and probably reach full growth in three years.

Behavior

When approached by an enemy, the Regal Horned lizard undergoes several diverting tactics such as head bobbing, push ups, and nodding. These actions are used to divert the opposition away from its territory, establish sex, and aid in species determination (Conant and Collins 1998). They are also used as courtship displays in attracting a mate. In the fall, they hibernate by burying themselves in the sand and emerge in the spring when the sun's rays have reached a certain temperature. The first few hours of the day are spent basking so their back is exposed to the sun. As soon as their body temperature rises to a specific degree, they commence foraging for food. As the heat of the day increases, they become more active (Seymour and Royo 1999). Members of the North American group of Regal Horned lizards have evolved an exceptionally bizarre defense against predators: when under threat they can restrict blood flow from the head until mounting pressure ruptures small blood vessels in and around the eyes, resulting in a spurt of blood that may leap a meter (3 1/2 feet) or more (Cogger and Zweifel 1998).

Food Habits

The Regal Horned lizard is diurnal. The lizard eats spiders, sowbugs, and other insects, especially ants. Their favorite is Harvester ants, which occupy about 88% of their stomach volume (Hodges 1998). Horned lizards do not take their food methodically, but instead take it in a toad-like fashion, with a flick of their long, sticky, tongue. After feeding, when ground temperatures become too hot, they seek the shade of a shrub, partially concealing themselves.

Conservation Status

The Regal Horned lizard populations are not protected. Four individuals may be collected in Arizona with a hunting license. However, habitat destruction and ant extermination are depriving the horned lizard not only of their homes, but of their only source of a dependable diet.

Contributors

Megan Kierzek (author), Michigan State University, James Harding (editor), Michigan State University.

Glossary

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

References

Cogger, H., R. Zweifel. 1998. Encyclopedia of Reptiles and Amphibians: A Comprehensive Illustrated Guide by International Experts. San Diego: Academic Press.

Conant, R., J. Collins. 1998. Reptiles and Amphibians of Eastern/Central North America. New York: Houghton Mifflin Company.

Hodges, W. 1999. "Phrynosoma solare" (On-line). Accessed November 15, 1999 at http://www.utc.cc.utexas.edu/~iffp475/phrynos_html/solare.html.

Seymour, G., A. Royo. 1999. "DesertUSA. Horned Lizard" (On-line). Accessed November 15, 1999 at http://www.desertusa.com/desert.html.