Phrynosoma cornutum, the Texas horned lizard, is the Texas State Reptile. It is one of fourteen species of horned lizards, unique iguanians belonging to the clade Phrynosomatidae. Horned lizards are readily distinguished from other lizards by their wide dorso-ventrally flattened body, skull adorned with a crown of horns, and spiny skin. Phrynosoma cornutum differs from other horned lizards (e.g., P. taurus) in having a single pair of occipital horns, two rows of lateral abdominal fringe scales, enlarged modified dorsal scales with four distinct keels, a single row of enlarged gular scales, and keeled ventral scales, and in lacking a postrictal scale.

Phrynosoma cornutum occurs in the midwestern and southern United States and northern Mexico. Its ranges from central Kansas, extreme southwestern Missouri, and the southeastern corner of Colorado southward and westward throughout most of Oklahoma and Texas (including coastal barrier islands), the southeastern half of New Mexico and the southeastern corner of Arizona to the Mexican states of Sonora, Chihuahua, Durango, Coahuila, Nuevo Leon, Tamaulipas, San Luis Potosi, and Zacatecas.

Horned lizards are unusual in that they are myrmecophagous - ant eaters - with blunt, noncuspid, peglike teeth for crushing prey. The diet of Phrynosoma cornutum consists of 69% harvester ants, with the remainder comprised of termites, beetles, and grasshoppers. Phrynosomatidae includes both oviparous (egg laying) and viviparous (live bearing) species; P. cornutum is oviparous, with a mean clutch size of 26.5 eggs.

Texas horned lizard populations have declined significantly in Texas and Oklahoma. The species has virtually disappeared in eastern and central portions of its range in Texas due to human disturbances, such as the conversion of habitat to agriculture and urban centers. The species will continue to decline in northern, central, and southern Texas as well as other portions of its range as urbanization expands. Other factors contributing to the decline of this species include the use of pesticides to kill ants and the invasion of the imported fire ant, Solenopsis invicta, which can overwhelm and kill juvenile horned lizards.

This specimen, an adult male of 87 mm snout-vent length, was collected by J. L. Reagan in 1948 in Bee County, Texas. It was made available to the University of Texas High-Resolution X-ray CT Facility for scanning by Ms. Wendy Hodges and Dr. David Cannatella of The University of Texas at Austin. Funding for scanning was provided by a National Science Foundation Digital Libraries Initiative grant to Dr. Timothy Rowe of The University of Texas at Austin.

The specimen was scanned twice. First, the entire specimen was scanned by Matthew Colbert on 17 May 2001 along the long axis of the body for a total of 246 slices, each slice 0.149 mm thick, with an interslice spacing of 0.149 mm. The second scan, of the head alone, was conducted along the coronal axis by Matthew Colbert on 18 May 2001 for a total of 348 slices, each slice 0.056 mm thick, with an interslice spacing of 0.056 mm. The dataset displayed was reduced for optimal Web delivery from the original, much higher resolution CT data.

Literature

Donaldson, W. L., A. H. Price, and J. Morse. 1994. The current status and future prospects of the Texas horned lizard (Phrynosoma cornutum) in Texas. Texas Journal of Science 46:97-113.

Frost, D. R., and R. Etheridge. 1989. A phylogenetic analysis and taxonomy of iguanian lizards (Reptilia: Squamata). University of Kansas Museum of Natural History Miscellaneous Publication 81.

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.

Price, A. H. 1990. Phrynosoma cornutum (Harlan): Texas horned lizard. Catalogue of American Amphibians and Reptiles 469.1-469.7.

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.

Links

Phrynosoma cornutum on The Animal Diversity Web (The University of Michigan Museum of Zoology)

Phrynosoma cornutum on the Texas Memorial Museum of Science and History's Herps of Texas

More on horned lizards from Eric Pianka and Wendy Hodges

The Horned Lizard Conservation Society