The flat-tail horned lizard (''Phrynosoma mcallii'') is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

lizard Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most Island#Oceanic isla ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Phrynosomatidae The Phrynosomatidae are a diverse family of lizards, sometimes classified as a subfamily (Phrynosomatinae), found from Panama to the extreme south of Canada. Many members of the group are adapted to life in hot, sandy deserts, although the spiny ...

. A species of

reptile Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...

, it is

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

to the

Sonoran Desert The Sonoran Desert () is a hot desert and ecoregion in North America that covers the northwestern Mexican states of Sonora, Baja California, and Baja California Sur, as well as part of the Southwestern United States (in Arizona and California). It ...

of the southwestern United States and northwestern Mexico. Its multiple

adaptations In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the p ...

for

camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...

help to minimize its shadow. The species is threatened, with a restricted range under pressure from human activities such as agriculture and development, and is specially protected in the United States.

Description and geographic range

The flat-tail horned lizard is named for United States Army Colonel George A. M'Call,Beolens, Bo; Watkins, Michael; Grayson, Michael (2011). ''The Eponym Dictionary of Reptiles''. Baltimore: Johns Hopkins University Press. xiii + 296 pp. . (''Phrynosoma mcallii'', p. 172). who collected the first specimen in

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

in the 19th century. The species occupies a small

range Range may refer to: Geography * Range (geographic), a chain of hills or mountains; a somewhat linear, complex mountainous or hilly area (cordillera, sierra) ** Mountain range, a group of mountains bordered by lowlands * Range, a term used to i ...

in the

of southeastern California, southwestern

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

, and extreme northern

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

in the

Baja California Baja California, officially the Free and Sovereign State of Baja California, is a state in Mexico. It is the northwesternmost of the 32 federal entities of Mexico. Before becoming a state in 1952, the area was known as the North Territory of B ...

and

Sonora Sonora (), officially Estado Libre y Soberano de Sonora (), is one of the 31 states which, along with Mexico City, comprise the Administrative divisions of Mexico, Federal Entities of Mexico. The state is divided into Municipalities of Sonora, 72 ...

states. Over time, horned lizard populations have adapted to climate, food, and predators, causing them to in some ways be distinct from one another. :"A medium-sized flat-bodied lizard with a wide oval-shaped body and scattered enlarged pointed scales on the upper body and tail. The back skin is smooth with small spines. 8 horns extend from the back of the head. The two central horns are long, slender and sharp. Long and narrow spines on the lower jaw and two rows of fringe scales on the sides of the body, the bottom row scales smaller than the upper."

Camouflage techniques

The flat-tail horned lizard has evolved elaborate

measures to eliminate

shadow A shadow is a dark area on a surface where light from a light source is blocked by an object. In contrast, shade occupies the three-dimensional volume behind an object with light in front of it. The cross-section of a shadow is a two-dimensio ...

. Their bodies are flattened, with the sides thinning to an edge; the animals habitually press their bodies to the ground; and their sides are fringed with white scales which effectively hide and disrupt any remaining areas of shadow there may be under the edge of the body. Different populations of the species match their local backgrounds using a combination of colour-creating cells in their back scales. These cells include black

melanophores Chromatophores are cells that produce color, of which many types are pigment-containing cells, or groups of cells, found in a wide range of animals including amphibians, fish, reptiles, crustaceans and cephalopods. Mammals and birds, in contrast ...

and red chromatophores in an upper layer, scattered over a layer of white reflective iridophores, enabling the flat-tail horned lizard to match the local soil or rock. So for example the Algondones Dunes population of San Luis, Sonora is generally redder than the population on the whiter Thousand Palms dunes of California. In addition, the dark midline helps to disrupt the outline of the lizard, resembling the thin shadows of plant stems in its windswept sand habitat.

A threatened species

The flat-tail horned lizard is threatened by development, agriculture, and other man-made intrusions into their small range. The majority of their remaining habitat in the US is administered by the Bureau of Land Management. The species (''Phrynosoma mcallii'' ) frequently coexists with sources of natural gas, oil, geothermal energy, and minerals which can found in its habitat. In 1982, the US Fish and Wildlife Service declared ''P. mcallii'' as a Candidate 2 Category for the list of threatened and endangered species due to concerns over potential threats to their habitat which could further diminish the population. ''P. mcallii'' has also been given special status in both California and Arizona, which prevents their collection. Experiments have been conducted to investigate the "fluctuations in populations of flat-tailed horned lizards, ''Phrynosoma mcallii'', in the Coachella Valley, California. This species has the smallest range of any horned lizard in the United States. In parts of its range, there are potentially conflicting activities, such as suburban development, agriculture, off-road recreation, and activities along the international border." "Between 1978 and 1980 the Bureau of Land Management supported investigations of the status of ''P. mcallii'' in California. The purpose of this work was to determine the local distribution and relative abundance of ''P. mcallii'', to correlate these parameters with various habitat attributes, and to gather information on the structure of the populations and mobility and food habits of individual lizards." The study also looked at the flat-tailed horned lizard's distribution and abundance throughout Arizona. The species was found to be restricted to an area of desert, 650–700 km² in size, in the southwestern corner of the state. The species was most abundant in places with the

Western whiptail The western whiptail (''Aspidoscelis tigris'') is a species of lizard in the Family (biology), family Teiidae. The species is found throughout most of the southwestern United States and northern Mexico. Most of its populations appear stable, and ...

(''Cnemidophorus tigris''), nests of the black harvester ant (''Messor pergandei''), galleta grass (''Hilaria rigida'') and sandy soils.

References

External links

Listing at CaliforniaHerps.com
{{Taxonbar, from=Q339057 Phrynosoma Reptiles described in 1852 Reptiles of the United States Reptiles of Mexico Fauna of the Sonoran Desert