CaliforniaHerps.com

A Guide to the Amphibians
and Reptiles of California


Flat-tailed Horned Lizard - Phrynosoma mcallii

Cope, 1896

(= Anota mcallii)
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Flat-tail Horned Lizard Range Map
Red: Range in California


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Map with California County Names





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
Flat-tail Horned Lizard Flat-tail Horned Lizard Flat-tail Horned Lizard Flat-tail Horned Lizard
Adult, Imperial County © Patrick Briggs Adult, Imperial County
© Patrick Briggs
Adult female, Imperial County
© Patrick Briggs
Adult, San Diego County
© Jason Jones
Flat-tail Horned Lizard Flat-tail Horned Lizard Flat-tail Horned Lizard Flat-tail Horned Lizard
Adults breeding in Imperial County
© Michael Robinson
Adult, Riverside County
(note researcher's tracking tag on tail)
© 2003 Bon Terra Consulting.
Adult head study, Imperial County
© Patrick Briggs
Adult, Imperial County © Paul Maier
Flat-tail Horned Lizard Flat-tail Horned Lizard horned lizard  
Juvenile, San Diego County
© Bruce Edley
Adult, Imperial County © Paul Maier Flat-tailed Horned Lizards are covered with small granular scales interspersed with larger pointed scales on the dorsal surfaces.  
       
Habitat
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.      
Description
 
Size
2.2 - 3.4 inches long from snout to vent (6.3 - 8.6 cm). (Stebbins, 2003)

Appearance
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.
Females are larger in size than males.
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

Activity
Diurnal.
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.

Horned lizards roam a home range, which may overlap with others and change seasonally, but male horned lizards do not defend their territory aggressively like other kinds of lizards. They don't have patches of brighly-colored scales to display to other males. Because they don't combat other males during the breeding season, their bodies are smaller than the bodies of female horned lizards, which lets them use their energy in searching for females instead of maintaining a large body size.
(Sherbrooke, 2003)
Defense
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.
Reproduction
Mates April to May.
Females lay one or two clutches of 3 - 10 eggs from  May to June.
Hybrids

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.

Habitat
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," or "Horned Toad"

Phrynosoma mcallii - Flat-tailed Horned Lizard (Stebbins 1985, 2003, 2012, 2018)
Phrynosoma m'calli - Flat-tailed Horned Lizard (Smith 1946, Stebbins 1954, 1966)
Phrynosoma m'callii - Flat-tailed Horned-toad (Doliosaurus mc'calli. Flat-tailed Horned Lizard; McCall's Horned Lizard; MacCall's Horned Toad.) (Grinnell and Camp 1917)

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.
Taxonomy
Family Phrynosomatidae Zebra-tailed, Earless, Fringe-toed, Spiny, Tree, Side-blotched, & Horned Lizards Fitzinger, 1843
Genus Phrynosoma Horned Lizards Wiegmann, 1828
Species

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
mcallii
- 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.

Flaxington, William C. Amphibians and Reptiles of California: Field Observations, Distribution, and Natural History. Fieldnotes Press, Anaheim, California, 2021.

Samuel M. McGinnis and Robert C. Stebbins. Peterson Field Guide to Western Reptiles & Amphibians. 4th Edition. Houghton Mifflin Harcourt Publishing Company, 2018.

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.

Joseph Grinnell and Charles Lewis Camp. A Distributional List of the Amphibians and Reptiles of California. University of California Publications in Zoology Vol. 17, No. 10, pp. 127-208. July 11, 1917.

Conservation Status

The following conservation status listings for this animal are taken from the July 2022 State of California "Special Animals List" and the July 2022 "State and Federally Listed Endangered and Threatened Animals of California" list, both of which are produced by multiple agencies and can be downloaded here: https://www.wildlife.ca.gov/Data/CNDDB/Plants-and-Animals.
You can check this link to see if there are more current lists.

A detailed explanation of the meaning of the status listing symbols can be found on the
Special Animals List. For quick reference, I have copied some of them on my Special Status Information page.

If no status is listed here, the animal is not included on either 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.

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

Vulnerable

NatureServe State Ranking S2

Imperiled

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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