A Guide to the Amphibians
and Reptiles of California

Flat-tailed Horned Lizard - Phrynosoma mcallii

Cope, 1896

(= Anota mcallii)
Click on a picture for a larger view

Flat-tail Horned Lizard Range Map
Range in California: Red

Dot-locality Range Map

observation link

Flat-tail Horned Lizard Flat-tail Horned Lizard
Adult, Imperial County Adult, Imperial County
Flat-tail Horned Lizard Flat-tail Horned Lizard Flat-tail Horned Lizard Flat-tail Horned Lizard
Adult aprox. 20 ft. below Sea Level, Imperial County Adult, Imperial County
Flat-tail Horned Lizard Flat-tail Horned Lizard Flat-tail Horned Lizard Flat-tail Horned Lizard
Adult, Imperial County Adult, Imperial County © Patrick Briggs
Flat-tail Horned Lizard Flat-tail Horned Lizard Flat-tail Horned Lizard Flat-tail Horned Lizard
Adult, San Diego County
© Jason Jones
Adult, Riverside County
(note researcher's tracking tag on tail)
© 2003 Bon Terra Consulting.
Adult, Imperial County
© Patrick Briggs
Adult female, Imperial County
© Patrick Briggs
Flat-tail Horned Lizard Flat-tail Horned Lizard Flat-tail Horned Lizard Flat-tail Horned Lizard
Juvenile, San Diego County
© Bruce Edley
Adults breeding in Imperial County
© Michael Robinson
Adult, Imperial County © Paul Maier Adult, Imperial County © Paul Maier
Flat-tail Horned Lizard horned lizard    
Adult head study, Imperial County
© Patrick Briggs
Flat-tailed Horned Lizards are covered with small granular scales interspersed with larger pointed scales on the dorsal surfaces.    
Flat-tail Horned Lizard Habitat Flat-tail Horned Lizard Habitat Flat-tail Horned Lizard Habitat Flat-tail Horned Lizard Habitat
Habitat, Imperial County

Cryptic adult in habitat,
(in the middle at the bottom)
Imperial County
Habitat, Imperial County Habitat during a wet spring with a good wildflower bloom, Imperial County (same area as the photo to the left.)
Flat-tail Horned Lizard Habitat Flat-tail Horned Lizard Sign    
Habitat, San Diego County Sign in Imperial County    
Short Video
Flat-tail Horned Lizard      
A Flat-tailed Horned Lizard runs rapidly across fine wind-blown sand and quickly buries itself with a final shake of its tail.      
2 1/5 - 3 2/5 inches long from snout to vent (6.3 - 8.6 cm). (Stebbins, 2003)

A medium-sized flat-bodied lizard with a wide oval-shaped body and enlarged pointed scales on the upper body and tail.
The tail is long and flattened.
The back skin is smooth with small spines.
8 horns extend from the back of the head.
The two central horns are long, slender and sharp.
Long and narrow spines on the lower jaw and two rows of fringe scales on the sides of the body, the bottom row scales smaller than the upper.
Color and Pattern
Color is light gray, tan, brownish, beige, or whitish above, matching the sand and soil.
There is a dark stripe down the middle of the back and usually dark spots running down each side of the stripe.
(This is the only horned lizard with a dark stripe on the back.)
The underside is white with no markings.

Life History and Behavior

Adapted to hot dry environments.
Can be active in very hot weather.
Able to run very quickly.
Does not squirt blood from eyes in defense like other horned lizards.
Population density is low and individuals have a relatively large home range.

Most adults apparently hibernate in the winter, but juveniles may remain active all year.
Most adults emerge in April, but some have been observed emerging in February and March.
They do not aestivate in Summer, but they will retreat into shallow burrows or rapidly shuffle from side to side to burrow into the sand in order to avoid extreme heat and cold.
When threatened, this lizard is capable of running away very quickly.
It will often stop and quickly bury itself in loose sand to hide, or sometimes it will run under a low bush or into a rodent burrow.
Its main defense is remaining motionless using its cryptic coloring to blend into the background and make it difficult to see. It will crouch down low to prevent shadows that could make it easier to see, and sit still to avoid detection.
Diet and Feeding
Eats mostly ants, especially Harvester ants, and occasionally other small invertebrates.

Although horned lizards may be desirable pets, captive animals normally do not live very long due to the difficulties of feeding them a proper diet of ants.
Mates April to May.
Females lay one or two clutches of 3 - 10 eggs from  May to June.

According to Leache and McGuire (2006) in their paper that described the species Phrynosoma goodei, P. mcallii hybridizes with P. goodei in the Yuma Desert.

Typical habitat is sandy desert hardpan or gravel flats with scattered sparse vegetation of low species diversity. Most common in areas with a high density of harvester ants and fine windblown sand, but rarely occurs on dunes.

Geographical Range

The historic range of this lizard is throughout most of the Colorado desert from the Coachella Valley south through the Imperial Valley and west into the Anza-Borrego desert, south to extreme NE Baja California, extreme SW Arizona and NW Sonora, Mexico.

Full Species Range Map\
Elevational Range
From below sea level to around 820 ft. in elevation.

Notes on Taxonomy
Leache and McGuire (2006, Molecular Phylog. Evolution 39:628-644) named four subclades of Phrynosoma - 3 in our area: Anota, Doliosaurus, and Tapaja.

Alternate and Previous Names (Synonyms)

Commonly called: "Horny Toad," "Horned Toad"

Phrynosoma m'callii - Flat-tailed Horned Lizard (Smith 1946, Stebbins 1966)

Conservation Issues  (Conservation Status)
"Threatened by a variety of human disturbances within its highly restricted range caused by agricultural, urban, and geothermal developments, extensive off-road vehicle use, sand and gravel mining, and other impacts." (Stebbins, 2003)

Federally protected since 1993, the Federal protection of P. mcallii was withdrawn in 2006.

California wildlife officials voted against putting P. mcallii on the endangered species list in December, 2016.
Family Phrynosomatidae Zebra-tailed, Earless, Fringe-toed, Spiny, Tree, Side-blotched, & Horned Lizards Fitzinger, 1843
Genus Phrynosoma Horned Lizards Wiegmann, 1828

mcallii Flat-tailed Horned Lizard Hallowell, 1852
Original Description
Phrynosoma mcallii - (Hallowell, 1852) Originally spelled "m'callii" - Proc. Acad. Nat. Sci. Philadelphia, Vol. 6, p. 182

from Original Description Citations for the Reptiles and Amphibians of North America © Ellin Beltz

Meaning of the Scientific Name
Phrynosoma - Greek - phrynos - toad and soma - body - refers to the squat, toad-like appearance
- honors Col. George A. M'Call of the U.S. Army who collected the lizard in the 1850's.

from Scientific and Common Names of the Reptiles and Amphibians of North America - Explained © Ellin Beltz
(and Sherbrooke 2003)

Related or Similar California Lizards
Phrynosoma platyrhinos calidiarum - Southern Desert Horned Lizard
Phrynosoma platyrhinos platyrhinos - Northern Desert Horned Lizard
Phrynosoma blainvillii - Blainville's Horned Lizard
Phrynosoma douglasii - Pygmy Short-horned Lizard

More Information and References
California Department of Fish and Wildlife

Horned Lizard Conservation Society

Stebbins, Robert C., and McGinnis, Samuel M.  Field Guide to Amphibians and Reptiles of California: Revised Edition (California Natural History Guides) University of California Press, 2012.

Stebbins, Robert C. California Amphibians and Reptiles. The University of California Press, 1972.

Stebbins, Robert C. A Field Guide to Western Reptiles and Amphibians. 3rd Edition. Houghton Mifflin Company, 2003.

Behler, John L., and F. Wayne King. The Audubon Society Field Guide to North American Reptiles and Amphibians. Alfred A. Knopf, 1992.

Powell, Robert., Joseph T. Collins, and Errol D. Hooper Jr. A Key to Amphibians and Reptiles of the Continental United States and Canada. The University Press of Kansas, 1998.

Bartlett, R. D. & Patricia P. Bartlett. Guide and Reference to the Turtles and Lizards of Western North America (North of Mexico) and Hawaii. University Press of Florida, 2009.

Jones, Lawrence, Rob Lovich, editors. Lizards of the American Southwest: A Photographic Field Guide. Rio Nuevo Publishers, 2009.

Smith, Hobart M. Handbook of Lizards, Lizards of the United States and of Canada. Cornell University Press, 1946.

Sherbrooke, Wade C. Horned Lizards, Unique Reptiles of Western North America. Southwest Parks and Monuments Association, 1981.

Sherbrooke, Wade C. Introduction to Horned Lizards of North America. University of California Press, 2003.

Lemm, Jeffrey. Field Guide to Amphibians and Reptiles of the San Diego Region (California Natural History Guides). University of California Press, 2006.

Grismer, L. Lee. Amphibians and Reptiles of Baja California, Including Its Pacific Islands and the Islands in the Sea of Cortés. The University of California Press, 2002.

Adam D. Leache, Jimmy A. McGuire. Phylogenetic relationships of horned lizards (Phrynosoma) based on nuclear and mitochondrial data: Evidence for a misleading mitochondrial gene tree. Molecular Phylogenetics and Evolution 39 (2006) 628–644.

Conservation Status

The following status listings are copied from the April 2018 Special Animals List and the 2017 Endangered and Threatened Animals List, both of which are published by the California Department of Fish and Wildlife.

If no status is listed here, the animal is not included on either CDFW list. This most likely indicates that there are no serious conservation concerns for the animal. To find out more about an animal's status, you can go to the NatureServe and IUCN websites to check their rankings.

Check here to see the most current complete lists.

P. mcallii was formerly listed as FPT - Federally proposed for listing as Threatened - but this was withdrawn 3/5/11.
Status Listing
NatureServe Global Ranking G3

Vulnerable—At moderate risk of extinction due to a restricted range, relatively few populations (often 80 or fewer), recent and widespread declines, or other factors.

NatureServe State Ranking S2

Imperiled in the state because of rarity due to very restricted range, very few populations (often 20 or fewer), steep declines, or other factors making it very vulnerable to extirpation from the state.

U.S. Endangered Species Act (ESA) None
California Endangered Species Act (CESA) None
California Department of Fish and Wildlife SSC Species of Special Concern
Bureau of Land Management S Sensitive
USDA Forest Service None
IUCN NT Near Threatened


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