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A Guide to the Amphibians
and Reptiles of California


Flat-tail Horned Lizard - Phrynosoma mcallii

Cope, 1896

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

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Flat-tail Horned Lizard Flat-tail Horned Lizard Flat-tail Horned Lizard
Adult aprox. 20 ft. below Sea Level, Imperial County
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
  Adult, Imperial County  
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
Flat-tail Horned Lizard Flat-tail Horned Lizard Flat-tail Horned Lizard
Juvenile, San Diego County
© Bruce Edley
Adult female, Imperial County
© Patrick Briggs
Adult, Imperial County
© Patrick Briggs
Flat-tail Horned Lizard horned lizard Flat-tail 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.

Adults breeding in Imperial County
© Michael Robinson
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 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 Flat-tail Horned Lizard Habitat
Habitat, San Diego County

Sign in Imperial County Habitat, 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 1/5 - 3 2/5 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 scattered enlarged pointed scales on the upper body and tail. 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 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 tail is long and flattened. The underside is white with no markings.
Behavior & Natural History
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.

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.

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.

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.
Diet
Eats mostly ants, especially Harvester ants, and occasionally other small invertebrates.
Reproduction
Mates April to May. One or two clutches of 3 - 10 eggs are laid May - June.

Know to hybridize with P. platyrhinos around Ocotillo and SE of Yuma. (Natureserve)
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.
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.

From below sea level to around 820 ft. in elevation.
Taxonomic Notes
Leache and McGuire (2006, Molecular Phylog. Evolution 39:628-644) named four subclades of Phrynosoma - 3 in our area: Anota, Doliosaurus, and Tapaja.
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.

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)

Alternate Names
"Horny Toad," "Horned Toad"

Related or Similar California Lizards
Phrynosoma platyrhinos calidiarum - Southern Desert Horned Lizard
Phrynosoma platyrhinos platyrhinos - Northern Desert Horned Lizard
Phrynosoma coronatum-Coast 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.

Conservation Status

The following status listings come from the Special Animals List and the Endangered and Threatened Animals List which are published by the California Department of Fish and Wildlife.


P. mcallii was formerly listed as FPT - Federally proposed for listing as Threatened - but this was withdrawn 3/5/11.
Organization
Status Listing
U.S. Endangered Species Act (ESA) None
California Endangered Species Act (CESA) None
California Department of Fish and Wildlife DFG:SSC California Species of Special Concern
Bureau of Land Management BLM:S Sensitive
USDA Forest Service USFS:S Sensitive

 

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