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Members of the Phrynosma douglassi complex. Photo
credit: R. Montanucci.
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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.
Citation
Montanucci, R. R. (2015). A taxonomic revision
of the Phrynosoma douglasii species complex (Squamata: Phrynosomatidae). Zootaxa, 4015(1),
1-177.