Phrynosoma taurus, the Mexican horned lizard, 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 taurus is differentiated from other horned lizard species (e.g., P. cornutum) by the following features: reduced occipital spines that are separated by a notch; posterolateral enlargement of the temporal area, ending in two heavy and moderately long horns; a single row of lateral abdominal fringe scales; nostrils placed inside the canthus rostralis; and reduced caudal vertebrae and concomitant short tail.

Phrynosoma taurus occurs in montane chaparral-oak forest of the Sierra Madre del Sur in Guerrero and in arid regions of Puebla and Oaxaca, Mexico. These lizards are called "el rey," "el toro," or "el torrito del Virgen" by local residents.

Horned lizards are unusual in that they are myrmecophagous - ant eaters - with blunt, noncuspid, peglike teeth for crushing prey. The diet of Phrynosoma taurus is 61% harvester ants, with the remainder comprised of other arthropods.

Phrynosomatidae includes both oviparous (egg laying) and viviparous (live bearing) species. Phrynosoma taurus was recently discovered to be viviparous (Zamudio and Parra-Olea, 2000); median clutch size along with other aspects of its reproductive biology are currently under study. Little is known of the ecology of this Mexican species, which is syntopic in parts of its range with another Mexican species, P. asio.

This specimen, a gravid female of 74 mm snout-vent length and 87 mm total length, was collected by Ms. W. L. Hodges in 1999 from the municipality of Eduardo Neri near Zumpango de Rio in the state of Guerrero, Mexico. It will be accessioned in the Museo de Zoología, Facultad de Ciencias, U. N. A. M., upon completion of Ms. Hodges' research. The specimen contains eight near-term embryos, four in each oviduct. It was made available to the University of Texas High-Resolution X-ray CT Facility for scanning by Ms. Hodges of the School of Biological Sciences 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 Department of Geological Sciences of The University of Texas at Austin.

The adult specimen was scanned twice. First, the entire specimen was scanned dorso-ventrally by Matthew Colbert on 07 May 2001 for a total of 225 slices, each slice 0.121 mm thick with an interslice spacing of 0.121 mm. The second scan, of the head alone, was conducted along the coronal axis by Matthew Colbert on 07 May 2001 for a total of 254 slices, each slice 0.086 mm thick with an interslice spacing of 0.086 mm.

Because this gravid female was scanned according to parameters ideal for her skeleton, little of the poorly ossified embryos is discernible in the renderings of her body; the light gray masses that are discernible in her abdominal cavity represent the paired statolithic masses and calcified endolymphatic sacs of each embryo.

Literature

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.

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.

Zamudio, K. R., and G. Parra-Olea. 2000. Reproductive mode and female reproductive cycles of two endemic Mexican horned lizards (Phrynosoma taurus and Phrynosoma braconnieri). Copeia 2000:222-229.

Links

More on horned lizards from Eric Pianka and Wendy Hodges

The Horned Lizard Conservation Society

Color animation of P. taurus showing the skin peeling away from the skeleton.