Phrynosoma ditmarsi, the rock horned lizard, lives in northern Mexico at rocky sites in oak and oak-pine woodlands and short-tree Sinaloan deciduous forest along the western aspect of the Sierra Madre Occidental in the state of Sonora, north of Yecora, at elevations of 1050-1425 meters. This species was 'lost to science' for 65 years: it was initially described at the end of the 19th century, but its limited distribution combined with an imprecise holotype locality record made it difficult to re-locate. Click here to read the story of its rediscovery. Phrynosoma ditmarsi can be distinguished from other horned lizard species by the following: occipital and temporal horns reduced to flaring expansions; deep and narrow occipital notch; high post-orbital ridge; large vertical expansion of the mandibles; bare tympanum in the anterior neck fold posterior to a vertical row of four spines; and one row of lateral abdominal fringe scales surrounded by prominent scales.
About the Species
This specimen (WLH 1133) was collected by Dr. Wendy Hodges on the steep hillsides 13 miles east of Baviacora, Rancho la Palma, Sonora, Mexico. It was made available to the University of Texas High-Resolution X-ray CT Facility for scanning by Dr. 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 specimen was scanned by Matthew Colbert on 27 May 2003 along the coronal axis for a total of 675 slices, each slice 0.0313 mm thick with an interslice spacing of 0.0313 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
The Horned Lizard Conservation Society