Vivariums;reptiles;Horned lizard

Horned lizard

Horned lizards are a genus (Phrynosoma) of lizards which are the type genus of the subfamily Phrynosomatinae. The horned lizard has been affectionately called a "horny toad", or "horned frog", though they are not moist-skinned toads or frogs. The common names come from the lizard's flattened, rounded body and blunt snout, which make it resemble a toad or frog (Phrynosoma means "toad-bodied"), as well as its tendency, in common with larger true frogs and toads, to move sluggishly, making them easy to hand-catch (such slow, undramatic movements may also avoid triggering attacks by predators, discussed later in this article). They are totally adapted to desert areas. The spines on its back and sides are made from modified reptile scales which prevent the water loss through the skin, whereas the horns on the heads are true horns (i.e. they have a bony core). Of 15 species of horned lizards in North America, eight are native to the United States. The largest-bodied and most widely distributed of the US species is the Texas horned lizard.

Horned lizards use a wide variety of means to avoid predation. Their coloration generally serves as camouflage. When threatened, their first defense is to remain still to avoid detection. If approached too closely, they generally run in short bursts and stop abruptly to confuse the predator's visual acuity. If this fails, they puff up their bodies to cause them to appear more horned and larger, so that they are more difficult to swallow. At least eight species (P. asio, P. cornutum, P. coronatum, P. ditmarsi, P. hernandesi, P. orbiculare, P. solare, and P. taurus) are also able to squirt an aimed stream of blood from the corners of the eyes for a distance of up to 5 feet (1.5 m).[1][2][3][4] They do this by restricting the blood flow leaving the head, thereby increasing blood pressure and rupturing tiny vessels around the eyelids. This not only confuses predators, but also the blood tastes foul to canine and feline predators. It appears to have no effect against predatory birds. Only three closely related species (P. mcallii, P. modestum, and P. platyrhinos) are certainly known to be unable to squirt blood.[2] To avoid being picked up by the head or neck, a horned lizard ducks or elevates its head and orients its cranial horns straight up, or back. If a predator tries to take it by the body, the lizard drives that side of its body down into the ground so the predator cannot easily get its lower jaw underneath.

Horned lizard

Scientific classification :

Kingdom:Animalia

Phylum:Chordata

Class:Reptilia

Order:Squamata

Suborder:Iguania

Family:Iguanidae

Subfamily:Phrynosomatinae

Genus:Phrynosoma
Wiegmann, 1828

The blood-squirting mechanism :

While previous thought held that compounds were added to the blood from glands in the ocular sinus cavity, current research has shown that the chemical compounds that make up the defense are already in the circulating blood.[2][3] It is possible that their diet of large quantities of venomous Harvester Ants could be a factor; however, the origin and structure of the chemicals responsible are still unknown. The blood-squirting mechanism increases survival after contact with canine predators;[3] therefore, it is probable that, while unorthodox, the trait could have provided an evolutionary advantage. Ocular autohemorrhaging has also been documented in other lizards,[5] which suggests blood-squirting could have evolved from a less extreme defense in the ancestral branch of the genus. Recent phylogenic research supports this claim, so it appears as though the species incapable of squirting blood have lost the adaptation for reasons yet unstudied.[6]

Population decline :

A University of Texas publication notes that,

Horned lizard populations continue to decline and disappear throughout the southwest despite protective legislation. The species most often noted for declining numbers is the Texas horned lizard which has disappeared from almost half of its geographic range.

Population declines are attributed to loss of habitat, human eradication of the ant populations upon which the lizards prey, displacement of native ant populations by invading fire ants (aided by synergistic effects of native ant eradication), and predation by domestic dogs and cats.[7]

Species and subspecies :

the horns on the heads are true horns

Giant horned lizard, Phrynosoma asio Cope, 1864
Short-tailed horned lizard, Phrynosoma braconnieri Duméril, 1870
Cedros Island horned lizard, Phrynosoma cerroense Stejneger, 1893
Texas horned lizard, Phrynosoma cornutum (Harlan, 1825)
Coast horned lizard, Phrynosoma coronatum
-Cape horned lizard, P. c. coronatum (Blainville, 1835)
-San Diego horned lizard, P. c. blainvillii Gray, 1839
-California horned lizard, P. c. frontale Van Denburgh, 1894
-Central peninsular horned lizard, P. c. jamesi Schmidt, 1922
-Northern peninsular horned lizard, P. c. schmidti Barbour, 1921
Ditmars' horned lizard or rock horned lizard, Phrynosoma ditmarsi Stejneger, 1906
Pygmy short-horned lizard, Phrynosoma douglasii

-P. d. brachycercum H.M. Smith, 1942
-P. d. douglasii (Bell, 1828)

Greater short-horned lizard, Phrynosoma hernandesi Girard, 1858
Flat-tail horned lizard, Phrynosoma mcallii (Hallowell, 1852)
Roundtail horned lizard, Phrynosoma modestum Girard, 1852

Texas horned lizard

Mexican Plateau horned lizard or Chihuahua Desert horned lizard, Phrynosoma orbiculare

-P. o. boucardii (Duméril & Bocourt, 1870)
-P. o. bradti Horowitz, 1955
-P. o. orbiculare (Linnaeus, 1789)
-P. o. orientale Horowitz, 1955
-P. o. cortezii (Bocourt, 1870)
-P. o. dugesii (Bocourt, 1870)
Desert horned lizard, Phrynosoma platyrhinos
-Southern desert horned lizard, P. p. calidiarum Cope, 1896
-Northern desert horned lizard, P. p. platyrhinos Girard, 1852
-Sonoran horned lizard, P. p. goodei Stejneger, 1893

Regal horned lizard, Phrynosoma solare Gray, 1845
Mexican horned lizard, Phrynosoma taurus Dugès, 1873
Gulf Coast horned lizard, Phrynosoma wigginsi Montanucci, 2004

Symbol :

The genus of horned lizards is the official state reptile of Wyoming.[8]

Texas designated the Texas horned lizard (Phrynosoma cornutum) as the official state reptile in 1993[9] and the "horned frog" is the mascot of Texas Christian University in Fort Worth, Texas. TCU is the only known athletic team with the "Horned Frog" as a mascot.

Comparison of P. modestum and P. platyrhinos

Phrynosoma douglasii

Video :

For the external links , refrences click here to read the full wikipedia article

Horned Lizared care and general Information articles :

Cute Horned Lizard in Stuttgart Zoo

1- Horned Lizards :

by Eric R. Pianka and Wendy L. Hodges

courtesy to : www.lifesci.utexas.edu/faculty/pianka/phryno.html

Erroneously called "horny toads," horned lizards are bizarre, spiny, ant-eating lizards unlike any other lizards in North America. Fourteen species are currently recognized, 8 of which are found within the continental USA (one reaches southern Canada), and 6 other little-known species are restricted to Mexico (one reaches Guatemala). Most horned lizard species are well represented in the fossil record by the Pleistocene (1 million years ago, mya), P. cornutum is found in the upper Pliocene (3 mya), and P. douglasi is known from the mid Miocene (15 mya). Three species went extinct in the late Pliocene-early Pleistocene, long before there were any humans. The genus is thought to have split from an ancestor shared with the sand lizards (Uma, Callisaurus, Cophosaurus, and Holbrookia) during the late Oligocene-early Miocene (23- 30 mya).

Humans and horned lizards have shared each other's company for thousands of years. This relationship is recorded from Anasazi, Hohokam, Mogollon, and Mimbres cultures through their use of horned lizard images on pottery, petroglyphs, effigy bowls, figures, and shells. Hopi, Navajo, Papago, Pima, Tarahumara and Zuni cultures portray horned lizards in their ceremonies and stories as symbols of strength. Piman people believe horned lizards can cure them of a staying sickness by appealing to the lizard's strength and showing their respect to the animal.

They formulate a cure by singing at a patient's side songs describing the lizards and their behaviors. A horned lizard fetish may be placed on an afflicted person's body during the songs. Native Mexican people also respect horned lizards attributing the words, "Don't tread on me! I am the color of the earth and I hold the world; therefore walk carefully, that you do not tread on me." A Mexican common name for horned lizards is "torito de la Virgen" or the Virgin's little bull. This name apparently was given to the lizards both because of their horns and because horned lizards are sacred to many people due to their blood squirting behaviors, otherwise considered weeping tears of blood.

These interesting lizards were first introduced to European audiences in 1651 by the Spaniard Francisco Hernandez. Hernandez was fortunate to observe a living individual which squirted blood from its eyes -- he noted this behavior in his report on the first scientific expedition to Mexico by Spain. Over a century later in 1767, a Mexican cleric of Spanish descent, Clavigero, also showed his wonder of horned lizards in his illustrated volumes of Mexican history. Still later, in 1828 Wiegmann coined the official scientific generic name Phrynosoma, which is Greek for toad-bodied (phrynos means "toad", soma means "body").

Species descriptions

Horned lizard species are distinct and easily recognized from each other. Arrangement of occipital and temporal horns on the head are enough to distinguish species, but other features such as number of rows of lateral, abdominal fringe scales and dorsal scale patterns are helpful, too. Color or color patterns generally are not good distinguishing features because these lizards are extremely variable and tend to match the color of the sand or rocks in their local environment. However, color can be used in certain circumstances as stated in species' descriptions below. The geographic ranges described below are based on historic records and do not reflect species' current distributions. Ranges of most species have been severely reduced.

Phrynosoma asio, Long Spined Horned Lizard

Diagnostic Characters:

Two rows of abdominal fringe scales
Three rows of large conical scales widely separated on the dorsum
Gular scales arranged in serrated longitudinal series
Large keeled ventral scales numbering 30-35 across the widest point constitute a formidable armor.

Geographic Distribution: This is the largest species attaining snout-to-vent length (SVL) of 115 mm and total length of 202 mm (8 inches). It occurs in southern Mexico from Colima through coastal Michoacan, Guerrero, Oaxaca, to Chiapas, and in the Balsas Basin. It is recorded from Guatemala.

Phrynosoma boucardi

Diagnostic Characters:

Two long occipital spines that project vertically
Temporal spines relatively long, projecting horizontally
Superciliary region elevated
Weakly keeled gular scales

While this species has been recognized as distinct, it has also been relegated to the subspecies P. orbiculare boucardi because the morphological characters that diagnose it are found on intermediate forms in the P. orbiculare group, although not all characters are found together.P. orbiculare is a wide ranging species and occurs very near specimens called P. boucardi More information is needed to sort out the taxonomy of P. boucardi.

Phrynosoma braconnieri

Diagnostic Characters:

One row of lateral abdominal fringe scales
Two moderately developed occipital spines, short, heavy, separated
Temporal horns very reduced
Very short tail
All ventral scales keeled
Nostrils in the line of the canthus rostralis

Geographic Distribution: This very rare horned lizard occurs in pine-oak woodland and xeric thorn-scrub of Puebla and Oaxaca, Mexico. It may inhabit Veracruz.

Phrynosoma cornutum: Texas horned lizard

Diagnostic Characters:

Single pair of occipital spines
Two rows of lateral abdominal fringe scales
Enlarged modified dorsal scales with 4 distinct keels
Single row of enlarged gular scales
Keeled non-mucronate ventral scales
Postrictal scale absent
White middorsal stripe

Geographic Range: From central Kansas, extreme southwestern Missouri, and the southeastern corner of Colorado southward and westward throughout most of Oklahoma and Texas (including coastal barrier islands), southeastern half of New Mexico and southeastern corner of Arizona to Mexican states of Sonora, Chihuahua, Durango, Coahuila, Nuevo Leon, Tamaulipas, San Luis Potosi, and Zacatecas.

Phrynosoma coronatum: Coast horned lizard

Diagnostic Characters:

Two rows of lateral abdominal fringe scales
Two occipital spines, 3-4 times longer than basal width, not in contact
4-5 temporal spines
Smooth ventral scales
Three or more rows of enlarged gular scales
Mate belly to belly

Geographic Range: From central California, west of the Sierra Nevada south throughout southern California, west of the Mojave desert, throughout Baja California, west of the Sierra Juarez and Sierra San Pedro Martir, Mexico. Up to six subspecies of P. coronatum have been recognized throughout its range. One subspecies has also been named a unique "species" (its taxonomic status is in doubt), P. cerroense, which occurs on the Pacific island, Isla de Cedros.

Phrynosoma ditmarsi: Rock horned lizard

Diagnostic Features:

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
One row of lateral abdominal fringe scales surrounded by prominent scales

Geographic Range: 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 about 65 years. Its unique habitat preferences and limited distribution, combined with a very imprecise holotype locality record made it difficult to locate. An extraordinary effort by Vincent Roth based on a cross-correlational analysis of gut contents from only three specimens led to its rediscovery.

Phrynosoma douglasi: Pygmy Short-Horned Lizard

Diagnostic Characters:

Specimens are very small in size
One row of lateral abdominal fringe scales
Head spines very short and reduced to tubercles, project vertically
Deep notch between occipital spines
Dorsal scales irregular in size and distribution, set in a rosette of smaller keeled scales

Geographic Range: This species is restricted to the Pacific Northwest in northern California, north through Washington to British Columbia, Canada and east through southeastern Idaho. Restricted to higher elevations.

Phrynosoma hernandezi: Short-horned lizard

Diagnostic Characters:

One row of lateral abdominal fringe scales
Reduced occipital spines directed posteriorly, parallel with temporal spines
Dorsal scales arranged in 6-8 longitudinal rows, rosettes absent or poorly developed.

Geographic Range: Wide ranging, P. hernandezi is found from southern Alberta, Canada, through Montana, Utah, Colorado, Arizona, New Mexico and into Mexico through northeastern Sonora, Chihuahua, and Durango. Restricted to higher elevations. Until recently, this species was previously included with P. douglasi.

Phrynosoma mcallii: Flat-tailed horned lizard :

Diagnostic Characters:

Flat and broad tail
Two or three rows of lateral abdominal fringe scales
Two elongate, sharp occipital horns 3-4 times longer than the basal horn width
Six temporal horns
Nostrils inside canthus rostralis
Tympana are not externally visible
Enlarged lateral row of gular scales
Olive or brown mid-dorsal stripe

Geographic Range: The original historical range is recognized as extending from the Coachella, Imperial, and Borrego Valleys in Riverside, Imperial, and extreme eastern San Diego Counties, California; west of the Gila and Tinajas Altas Mountains and south of the Gila River, Yuma County, Arizona; northeastern Baja California, east of Sierra de Juarez and north and west of Bahia de San Jorge in Sonora, Mexico. The distribution of this species is now much more restricted.

Phrynosoma modestum: Round-tailed horned lizard

Diagnostic Characters:

Tail round in cross section
No lateral abdominal fringe scales
Four occipital horns short and equal in length
Ear concealed in some, exposed in others
Chin shields contact infralabials throughout
Solid, pale coloration, white, tan, or pink
Dorsal marks restricted to dark neck patches, dark tail bands, some shadowing around limbs
Unique rock mimicry behavior

Geographic range: Western half of Texas, north to Albuquerque, New Mexico, west to southeastern Arizona, south through northeastern Sonora, most of Chihuahua, through the northern third of Durango, to northern Zacatecas and northeastern Nuevo Leon, Mexico.

Phrynosoma orbiculare: Chihuahua desert horned lizard

Diagnostic Characters:

One row of lateral abdominal fringe scales
Two short occipital horns
Temporal horns extend nearly as far as occipital horns
Smooth ventral scales
Very short tail

Geographic Range: This wide ranging Mexican species is found on the northern plateau from Chihuahua, Durango, Nuevo Leon, southeast through Morelos, Puebla and Veracruz.

Desert horned lizard, Phrynosoma platyrhinos.

Phrynosoma platyrhinos: Desert horned lizard

Diagnostic Characters:

One row of lateral abdominal fringe scales
Two moderately elongated occipital horns, not in contact at base
Enlarged chin shields
Nostrils inside the canthus rostralis
Blunt snout

Geographic Range: Lowland deserts in southeastern Oregon, southwestern Idaho through Nevada, western Utah, California, Arizona, south barely into northern Baja California and northern Sonora, Mexico.

Phrynosoma solare: Regal horned lizard

Diagnostic Characters:

One row of lateral abdominal fringe scales
Four large occipital horns, in contact at base and continuous with six temporal horns forming a large crown of ten horns.
Nostrils inside the canthus rostralis
Ventral scales keeled

Geographic Range: The species is restricted to Sonoran desert in south-central Arizona, east to extreme southwestern New Mexico, south through most of Sonora (including Isla Tiburon) and into northern Sinaloa, Mexico.

Phrynosoma taurus:

Diagnostic Characters:

One row of lateral abdominal fringe scales
Occipital spines reduced and separated by a notch
Temporal area greatly enlarged posterolaterally, ending with two heavy, moderately long spines
All ventral scales keeled
Nostrils inside the canthus rostralis

Geographic Range: Little is known about this species. It is found in montane chaparral-oak forest and desert areas of the Sierra Madre del Sur, south and southeast of Mexico City, in Guerrero and Puebla, Mexico.

Geographic distributions of egg laying species.

Geographic distributions of live-bearing species.

Phylogeny and Natural History

Phylogeny allows us to trace evolutionary history and relationships of organisms. Much like humans draw their genealogies, or family trees, to discover where their blue eyes or baldness came from, or perhaps whether they are genetically predisposed for cancer -- systematists construct such trees to show how different species have evolved. Ecologists use phylogenetic relationships to learn how characteristics of species evolved, or how different species acquired traits and evolved to occupy their current niche. Principles of parsimony are used to identify the simplest explanations for how a trait evolved.

There are two major lineages of horned lizards, one of which lay eggs (oviparous) while members of the other group give birth to living young (viviparous). Although the ancestral state is oviparity, one lineage of horned lizards, all high altitude species, has evolved live bearing (braconnieri, boucardi, ditmarsi, douglasi, hernandezi, orbiculare, and probably taurus). Viviparity appears to have arisen only once in the genus, rather than independently 5 times. Interestingly, all species are montane which provides support for the idea that drier and colder mountain climates demand that montane lizards retain their progeny internally until birth rather than laying eggs.

Two hypothetical phylogenies for horned lizards.

Horned lizards are a rather fecund group, and lay or give birth to many offspring compared to other lizards. The median clutch size for P. cornutum is 25 (one specimen laid 40 eggs!), P. asio lays 17 on average, and P. hernandezi bears up to 16 live lizards. Reproductive effort measures the resources given to producing offspring and is often measured by comparing the weight or volume of the offspring to female volume or body weight (relative clutch mass, or RCM). RCM among horned lizards ranges from 13% to 35%, (offspring constitute from 13-35% of a female's weight). Females can have a few large versus many small progeny. Some species also reproduce twice in a season. This large investment in offspring throughout the active season weighs down females and makes them vulnerable to predators. Because babies are tiny and easy prey for a multitude of predators, horned lizards would go extinct without such high fecundities.

An interesting more recent analysis of horn lengths among horned lizards is shown in the above figure from Leache and Maguire (2006). Preferred phylogeny for Phrynosoma based on combined mtDNA and nuclear data. The most parsimonious reconstruction of antipredator blood-squirting (ABS) is mapped on the phylogeny (black bars). Blood squirting behavior was ancestral and has been lost 4 times. Silhouettes of Phrynosoma heads are shown to illustrate the variation in cranial horn anatomy, color coded to correspond to relative horn length (ancestral state reconstructions mapped on each node). The asterisk adjacent to P. taurus indicates that the effective length of the squamosal horns of this unusual species are longer than portrayed by the measuring technique employed. Four Phrynosomaclades, TAPAJA, ANOTA, DOLIOSAURUS, and BREVICAUDA are marked (from Leache and Maguire 2006).

Horned lizards have evolved a variety of mechanisms to avoid their predators which include loggerhead shrikes, hawks, roadrunners, a variety of snakes, coyotes and foxes. Their first line of defense is to remain cryptically hidden from a predator's sight. This is accomplished by three things, matching the background color of the substrate, possessing various spines and fringes of scales which decrease their shadows, and they remain motionless when approached. Secondly, their formidable body armor of spines and horns pose a significant threat to many predators as witnessed by snakes and birds found dead with lizards' horns projecting through predators' throats. Horned lizards will capitalize on their armor by inflating their bodies with air until they look like spiny balloons. At least four species of horned lizards (but not all species), coronatum, cornutum,

Still Courtesy to : www.lifesci.utexas.edu/faculty/pianka/phryno2.html

The Adaptive Suite of Horned Lizards

Various features of horned lizard anatomy, behavior, diet, temporal pattern of activity, thermoregulation, and reproductive tactics can be profitably interrelated and interpreted to provide an integrated view of the ecology of these interesting lizards. Horned lizards are ant specialists. Some species eat essentially nothing else, while other species eat a variety of other insects. Ants are small and contain much indigestible chitin, so that large numbers of them must be consumed. Hence an ant specialist must possess a large stomach for its body size. Consider the desert horned lizard Phrynosoma platyrhinos in greater detail. When expressed as a proportion of total body weight, the stomach of this horned lizard occupies a considerably larger fraction of the animal's overall body mass (about 13 percent) than do stomachs of all other sympatric desert lizard species, including the herbivorous desert iguana Dipsosaurus dorsalis (herbivores typically have lower assimilation rates and larger stomachs than carnivores).

The adaptive suite of horned lizards.

Possession of such a large gut necessitates a tank-like body form, reducing speed and decreasing the lizard's ability to escape from predators by flight. As a result, natural selection has favored a spiny body form and cryptic behavior rather than a sleek body and rapid movement to cover (as in the majority of other species of lizards). Risks of predation are likely to be increased during long periods of exposure while foraging in the open. A reluctance to move, even when actually threatened by a potential predator, could well be advantageous. Movement might attract attention of predators and negate the advantage of concealing coloration and contour. Such decreased movement doubtless contributes to the observed high variance in body temperature of Phrynosoma platyrhinos which is significantly greater than that of all other species of sympatric lizards.

To make use of this patchy and spatially concentrated, but at the same time not overly nutritious, food supply, P. platyrhinos has evolved a unique constellation of adaptations that include a large stomach, spiny body form, an expanded period of activity, and "relaxed" thermoregulation (eurythermy). The high reproductive investment of adult horned lizards is probably also a simple and direct consequence of their robust body form. Lizards that must be able to move rapidly to escape predators, such as whiptail lizards (Cnemidophorus), would hardly be expected to weight themselves down with eggs to the same extent as animals like horned lizards that rely almost entirely upon spines and camouflage to avoid their enemies.

Texas horned lizard, Phrynosoma cornutum.

Convergent Evolution and Ecological Equivalents

Organisms filling similar ecological niches in different, independently-evolved, biotas are termed "ecological equivalents." Such convergent evolutionary responses of lizards to desert environments, although imperfect, are evident between continents. As a striking example, Australian and North American deserts both support cryptically-colored and thornily-armored ant specialized species: the agamid Moloch horridus exploits this ecological role in Australia, while its counterparts, Phrynosoma, occupy the role in North America. No other desert lizards have adopted such a life style, anywhere else on Earth.

Interestingly enough, a morphometric analysis demonstrates that Moloch and Phrynosoma are actually anatomically closer to one another than either species is to another member of its own lizard fauna to which they are much more closely related. Hence, thorny devils and horned lizards have converged on the same body plan and ecological roles.

When the natural history of Moloch is scrutinized carefully, numerous differences from Phrynosoma become apparent. Body temperatures of active Moloch are not as variable as those of Phrynosoma, nor are their stomachs as large. Yet Moloch are even more specialized than Phrynosoma, feeding only on very small Iridomyrmex ants. Ants are much more abundant in the Australian deserts than they are in North America.

British naturalist W. Saville-Kent kept Moloch in captivity in the late 1890's before anyone had studied Phrynosoma. He discovered that these bizarre agamid lizards fed almost exclusively on ants and made various observations on their natural history. Noting the striking morphological similarity between Moloch and the North American genus Phrynosoma, Saville-Kent predicted that members of the latter genus would be ant specialists. His prediction proved quite correct.

A Mexican horned lizard, Phrynosoma orbiculare.

Conservation :

Many features of the horned lizard adaptive suite outlined above show how well suited these lizards are to their natural environment. They are a variable group of lizards and live in a wide variety of habitats and geographic regions. Unfortunately, when removed from their habitat or if their habitat is altered, horned lizards soon perish. In 1967, the progressive Texas legislature passed protective legislation preventing collection, exportation and sale of Phrynosoma cornutum from the state. Prior to this legislation, hundreds of thousands of horned lizards were exported (dead and alive) from Texas every summer to tourists, curiosity seekers and would be pet owners, leading only to demise of the lizards.

A Mexican horned lizard, Phrynosoma asio.

If a horned lizard has adequate fat reserves, it can live for months in an inadequate captive environment. These lizards are notoriously difficult to maintain for any length of time in captivity, however. Most species are now protected by state laws from general collection, although the state of Nevada still ignorantly allows commercial exploitation of Phrynosoma. Kids earn 25 cents to $1.00 for each lizard which commercial merchants turn around and resell for $20-30 to hobbyists. Nice profit margin, but certain death for almost all the collected lizards. Mexican nationals also find Phrynosoma irresistible as "pets" and they collect and attempt to keep them in captivity in higher numbers than ever. Phrynosoma are becoming prevalent in Mexican markets throughout the country despite limited federal protection.

Horned lizard populations continue to decline and disappear throughout the southwest despite protective legislation. The species most often noted for declining numbers is the Texas horned lizard which has disappeared from almost half of its geographic range.

However, Phrynosoma coronatum and P. mcallii populations also suffer from dramatic habitat loss due to human encroachment. P. mcallii had a narrow geographic range to begin with and has lost half of its historic habitat in the last few decades

-- every day, several more acres of its habitat are converted to golf courses, strip malls and agricultural fields in California, Arizona and Mexico. Habitat loss is the most obvious source of population loss because no habitat means no lizards, but habitat alteration also has very detrimental effects.

Round-tailed horned lizard, Phrynosoma modestum (L. J. Vitt).

Habitat alteration occurs at a variety of levels. Housing developments do not always mean certain demise of horned lizards if native vegetation is kept and other pets, such as dogs and cats are not allowed. Many small Texas towns rightfully boast of their amazing horned lizard populations. But, generally developments mean planting non-native grasses which completely cover the ground, choking out native plants and preventing the lizards access to dirt to bury in or dig their burrows or lay eggs. Along with developments, generally come a new set of animals not native to the area. The spread of ravens throughout the deserts, blue jays, dogs, and cats are promoted by human invasion. These animals follow humans around. Trash pits become havens and resources to increase not only avian predators, but canine predators as well.

Developments mean paved roads and fast cars. Horned lizards, like many other reptiles, like to bask on roads, a dangerous predilection for lizards whose primary defense against predators (cars in this case) is not to move. A small paved military road in the Arizona desert attests to the deadly affect of roads on horned lizards -- a full one quarter of all flat-tailed horned lizards seen on this road were dead due to vehicle impact. Roads are usually lined with fences and utility poles, both great perch sites for avian predators to sit and watch for lizards trying to cross or bask on the open road.

Habitat alteration can also take the form of agricultural conversion or conversion to pastureland. Habitat alteration in Texas and the southeastern United States has promoted the spread of a terrible introduced pest, Solenopsis invicta, the red imported fire ant. These ants, accidentally introduced from South America, pose a significant threat to all wildlife in the southern United States. Fire ants can kill almost anything given the chance and they are fierce competitors against native ants which horned lizards require for food. Horned lizards do not eat fire ants probably due to the ants' different natural history than the native harvesting ants, different venom in the sting apparatus and different nutritional component. The widespread invasion of fire ants have given all ants a very bad reputation. Since the early 1950s, broadcast pesticides have been used to combat ants and other pest insects, including mosquitoes and crop pests.

Homeowners regularly use ant insecticides to kill all ants on their property thereby making it even easier for fire ants to invade because they have nothing to stop them. Such practices also demolish the food supply for horned lizards. The Horned Lizard Conservation Society (P.O. Box 122, Austin, Texas, 78767) was formed in 1990 to try to stop the decline of horned lizards in North America.

Regal horned lizard, Phrynosoma solare (L. J. Vitt).

Horned lizards are unique lizards in the world. They were here long before humans and have evolved through many millions of years of environmental changes. Unfortunately, horned lizards cannot cope with the rapid, drastic human modifications of the landscape occurring today. Protecting natural areas and reducing human impact on those areas is vital for the continuance of horned lizards to be a part of the human experience. Moreover, observing wild horned lizards in their natural environments is even more rewarding than watching them sit captive in small terrariums.

References/Suggested Reading

Donaldson, W. L., A. H. Price, and J. Morse. 1994. The Current Status and Future Prospects of the Texas Horned Lizard (Phrynosoma cornutum) in Texas. Texas Journal of Science 46(2) 97-113.

Funk, R.S. 1981. Phrynosoma mcallii (Halowell): Flat-tailed horned lizard. Cat. Amer. Amph. Rept. pp. 281.1-281.2.

Hodges, W.L. 1995. Phrynosoma ditmarsi Stejneger: Rock Horned Lizard. Catalogue of American Amphibians and Reptiles. pp. 614.1-614.3

Hodges, W.L., Zamudio, K.R., 2004. Horned lizard (Phrynosoma) phylogeny inferred from mitochondrial genes and morphological characters: understanding conflicts using multiple approaches. Mol. Phylogent. Evol. 31: 961-971.

Jennings, M. R. 1988. Phrynosoma coronatum (Blainville): Coast horned lizard. Cat. Amer. Amph. Rept. pp. 428.1-428.5.

Jennings, M. R. 1988. Phrynosoma cerroense (Stejneger): Cedros Island horned lizard. Cat. Amer. Amph. Rept. pp. 427.1-427.2

Leache, A.D. and J. A. McGuire. 2006. Phylogenetic relationships of horned lizards (Phrynosoma) based on nuclear and mitochondrial data: Evidence for a misleading mitochondrial gene tree. Molecular Phylogenetics and Evolution 39: 628-644.

Manaster, J. 1997. Horned Lizards. University of Texas Press, Austin, Texas.

Montanucci, R. R., 1989. The relationship of morphology to diet in the horned lizard genus Phrynosoma. Herpetologica 45: 208-216

Montanucci, R. R., 1987. A phylogenetic study of the horned lizards, genus Phrynosoma, based on skeletal and external morphology. Contrib. Sci., Nat. Hist. Mus. L.A. Co. 390:1-36

Parker, W.S. 1974. Phrynosoma solare (Gray): Regal horned lizard. Cat. Amer. Amph. Rept. pp. 162.1-162.2.

Pianka, E. R. 1991. Phrynosoma platyrhinos. Girard: Desert Horned Lizard. Catalogue of American Amphibians and Reptiles. pp. 517.1-517.4.

Pianka, E. R. and W. S. Parker. 1975. Ecology of horned lizards: A review with special reference to Phrynosoma platyrhinos. Copeia 1975: 141-162. Download pdf

Price, A. H. 1990. Phrynosoma cornutum (Harlan): Texas Horned Lizard. Catalogue of American Amphibians and Reptiles. 469.1-469.7.

Reeve, W. L. 1952. Taxonomy and distribution of the horned lizard genus Phrynosoma. Univ. Kansas Sci. Bull. 34: 817-960.

Sherbrooke, W. C. 1981. Horned lizards, unique reptiles of western North America. Southwest Parks & Mon. Assoc., Globe, Ariz. 48 pp.

Smith, H. M. 1946. Handbook of lizards: Lizards of the United States and of Canada. Comstock Publishing Co. Ithaca, New York.

Welch, J. R. 1993. O Ye legendary Texas Horned Frog! Yellow Rose Press. Irving, Texas.

Zamudio, K. R., K. B. Jones, and R. H. Ward. 1997. Molecular systematics of short-horned lizards: biogeography and taxonomy of a widespread species complex. Systematic Biology 46: 284-305.

Horned lizard .. Introduction , descriptions & care in captivity .. PART 1 .. PART 2

Species and subspecies:

Vivarium & Terrarium Creatures ..

Horned lizard .. Introduction , descriptions & care in captivity .. PART 1 .. PART 2

Species and subspecies: