Members of the Phrynosma douglassi complex. Photo
credit: R. Montanucci.
Horned Lizards of the genus Phrynosoma are perhaps the most novel North American lizards. One species group, the Short-horned lizards (the Phrynosoma douglasii species complex) occur throughout the inter-montane West and Great Plains of western North America. In a new paper, Montanucci (2015) has reviewed the taxonomy of these lizards, using comparative morphology and color pattern variation in 3,174 specimens. Multivariate analyses of 20 morphological and color-pattern characters were applied to 977 specimens, and univariate statistics were summarized for 52 samples totaling 1,134 specimens. The results support the recognition of Phrynosoma douglasii (Bell 1828) as a distinct species, and the resurrection of P. brevirostris Girard 1858 and P. ornatissimum Girard 1858 as species distinct from Phrynosoma hernandesi Girard 1858.
Phrynosoma brevirostris is found in sagebrush and short-grass communities as well as in open canopy conifer savanna at higher elevations. Two new species allied to Phrynosoma brevirostris were described. Phrynosoma bauri from the eastern plains of Colorado and northeastern New Mexico, southeastern Wyoming and southwestern Nebraska south of the North Platte River inhabits areas dominated by Grama-buffalo grass to Juniper-pinyon woodland, and Pine-Douglas fir. The second species allied to P. brevirostris is Phrynosoma diminutum, a species endemic to the San Luis Valley of southern Colorado and northern New Mexico. The Mexican taxon brachycercum Smith is reassigned as a subspecies of Phrynosoma ornatissimum. The ranges of Phrynosoma hernandesi and P. ornatissimum broadly overlap in central New Mexico, the former occupying the coniferous forests of disjunct mountain ranges, the latter occurring in the surrounding desert grasslands.
Principal components analysis suggests morphological evidence for hybridization where the two taxa meet, often within ecotones between montane forest associations and grasslands. Principal components analysis also revealed a high level of morphological variability in the Colorado Plateau region of northeastern Arizona, northwestern New Mexico, extreme southwestern Colorado and adjacent Utah. The evidence suggests that these populations arose through past hybridization between the two species.
The taxon ornatum Girard 1858, although sharing several traits with Phrynosoma brevirostris, is morphologically close to P. hernandesi. It is regarded as a stabilized population of hybrid origin, but treated as a subspecies of Phrynosoma hernandesi.
Phrynosoma douglasii inhabits Sagebrush steppe over much of the Columbia Plateau of eastern Washington based on museum records. It has been reported only from the sagebrush regions of southeastern Washington. The dense, low to medium tall grass may have precluded the establishment of short-horned lizard populations over much of this habitat, except where exposed, friable soils were present. In Oregon, populations east of the Cascades occur in Sagebrush steppe, but in the vicinities of Lake Abert and Fossil Lake, the lizards have also been collected in Saltbush-greasewood association. In the Cascade Range, populations occur in open conifer forest, including Silver fir-Douglas fir forest and Fir-hemlock forest on the western slopes, and Grand fir-Douglas fir forest, and Ponderosa shrub forest on the eastern slopes above the Sagebrush steppe.
Phrynosoma douglasii inhabits open-canopy forests with widely spaced trees and well-drained, friable soils. Dense forests, with closed canopies, impede the establishment of populations. In southern Idaho, known localities are dominated by sagebrush steppe, and as yet, there are no confirmed records in Douglas fir forest and Western spruce-fir forest in the mountain ranges north of the Snake River Plain.
Phrynosoma h. hernandesi ranges from northern Sonora (recorded as far south as Sierra de la Madera) through the isolated mountain ranges and grasslands of southeastern Arizona northward along the Mogollon Rim. It ranges across the Coconino and Kaibab plateaus and follows the Wasatch Range in Utah. It occurs in the Pavant Range west of the Sevier River, and in the Henry Mountains northeast of the Escalante River, but presently there are no records from the Uinta Mountains in Utah. In northwestern Arizona there are records for the Hualapai and Cerbat mountains, Shivwits Plateau (near Snap Point) and the Mount Trumbull area.
The taxonomic arrangement in this study, with the exception of P. douglasii, is largely discordant with the proposed taxonomy from a previously published study based on mitochondrial DNA sequence data.
Montanucci, R. R. (2015). A taxonomic revision of the Phrynosoma douglasii species complex (Squamata: Phrynosomatidae). Zootaxa, 4015(1), 1-177.