Phrynosoma mcallii, the flat-tailed horned lizard, historically occurred in the Coachella, Imperial, and Borrego Valleys in Riverside, Imperial, and extreme eastern San Diego counties, California; west of the Gila and Tinajas Altas Mountains and south of the Gila River in Yuma County, Arizona; and in northeastern Baja California, east of Sierra de Juarez and north and west of Bahia de San Jorge in Sonora, Mexico. Its distribution is now much more restricted. P. mcallii can be distinguished from other horned lizard species by the following: flat and broad tail; two or three rows of lateral abdominal fringe scales; two elongate, sharp occipital horns 3-4 times longer than the basal horn width; six temporal horns; nostrils inside canthus rostralis; tympana not externally visible; enlarged lateral row of gular scales; and olive or brown mid-dorsal stripe.
About the Species
This specimen (TNHC 062316) was collected by Cameron Barrows 1 kilometer West of Washington Street, Thousand Palms Unit of Coachella Valley Preserve System, Riverside County, California. It was made available to the University of Texas High-Resolution X-ray CT Facility for scanning by Dr. Wendy Hodges of the Department of Biology, University of California, Riverside. Funding for scanning was provided by a National Science Foundation grant (DBI-0204459) to Dr. Hodges. Funding for image processing was provided by a National Science Foundation Digital Libraries Initiative grant to Dr. Timothy Rowe of the Department of Geological Sciences, The University of Texas at Austin.
About this Specimen
The head of the specimen was scanned by Matthew Colbert on 10 June 2003 along the coronal axis for a total of 729 slices, each slice 0.0278 mm thick with an interslice spacing of 0.0278 mm.
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Pianka, E. R., and W. S. Parker. 1975. Ecology of horned lizards: A review with special reference to Phrynosoma platyrhinos Copeia 1975:141-162.
Presch, W. 1969. Evolutionary osteology and relationships of the horned lizard genus Phrynosoma (Family Iguanidae) Copeia 1969:250-275.
Reeve, W. L. 1952. Taxonomy and distribution of the horned lizard genus Phrynosoma. University of Kansas Science Bulletin 34:817-960.
Smith, H. M. 1946. Handbook of Lizards: Lizards of the United States and of Canada. Comstock Publishing Co., Ithaca, New York.
More on horned lizards from Eric Pianka and Wendy Hodges
Phrynosoma mcallii page from the California Department of Fish and Game
Images of P. mcallii on californiaherps.com
The Horned Lizard Conservation Society