Horned lizard

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Template:Short description Template:About Template:Automatic taxobox Phrynosoma, whose members are known as the horned lizards, horny toads, or horntoads, is a genus of North American lizards and the type genus of the family Phrynosomatidae. Their common names refer directly to their horns or to their flattened, rounded bodies (squat bodied), and blunt snouts.

The generic name Phrynosoma means "toad-bodied". In common with true toads (amphibians of the family Bufonidae), horned lizards tend to move sluggishly, often remain motionless, and rely on their remarkable camouflage to avoid detection by predators. They are adapted to arid or semiarid areas. The spines on the lizard's back and sides are modified reptile scales, which prevent water loss through the skin, whereas the horns on the head are true horns (i.e., they have a bony core). A urinary bladder is absent.<ref>Mader's Reptile and Amphibian Medicine and Surgery</ref> Of the 21 species of horned lizards, 15 are native to the US. The largest-bodied and most widely distributed of the American species is the Texas horned lizard.

Defenses

File:Phrynosoma orbiculare 1.jpg
Mexican Plateau horned lizard (Phrynosoma orbiculare) near Xalapa de Enríquez, Veracruz, Mexico, showing blood squirted from the eye as defensive behavior (20 April 2011)

Horned lizards use a variety of means to avoid predation. Their coloration generally serves as camouflage. When threatened, their first defense is to remain motionless 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.<ref>Template:Cite journal</ref>

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 up to Template:Convert.<ref name="Middendorf III et al., 2001"/><ref name="Sherbrooke & Middendorf III, 2001"/><ref name="Sherbrooke & Middendorf III, 2004"/><ref name=hodges/> They do this by restricting the blood flow leaving the head, thereby increasing blood pressure and rupturing tiny vessels around the eyelids. The blood not only confuses predators but also 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 either be unable to squirt blood or only do it extremely rarely.<ref name="Sherbrooke & Middendorf III, 2001"/>

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.<ref name="Sherbrooke & Middendorf III, 2001"/><ref name="Sherbrooke & Middendorf III, 2004"/> 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;<ref name="Sherbrooke & Middendorf III, 2004"/> the trait may provide an evolutionary advantage. Ocular autohemorrhaging has also been documented in other lizards,<ref name="Sherbrooke, 2000"/> 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 the species incapable of squirting blood apparently have lost the adaptation for reasons yet unstudied.<ref name="Leaché and McGuire (2006)"/>

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.Template:Citation needed

Population decline

File:Phrynosoma douglasii 4220.JPG
Phrynosoma douglasii

A University of Texas publication notes that horned lizard populations continue to disappear throughout their distribution despite protective legislation. Population declines are attributed to a number of factors, including the fragmentation and loss of habitat from real estate development and road construction, the planting of non-native grasses (both suburban and rural), conversion of native land to pastureland and agricultural uses, and pesticides. Additionally predation by domestic dogs and cats place continued pressure upon horned lizards.<ref name=Pianka>Template:Cite web</ref>

Fire ants (Solenopsis invicta), introduced from South America via the nursery industry's potted plants, pose a significant threat to all wildlife including horned lizards. Phrynosoma species do not eat fire ants. Fire ants kill many species of wildlife, and are fierce competitors against the native ants, which horned lizards require for food (with their specialized nutritional content). Fire ants have given all ants a bad reputation, and human attempts to eradicate ants, including invasive species and the native species on which the lizards prey, contribute to the continued displacement of native ant species and the decline of horned lizards.<ref name=Pianka/>

The Texas horned lizard (Phrynosoma cornutum) has disappeared from almost half of its geographic range. Their popularity in the early to mid-20th-century pet trade, where collectors took thousands from the wild populations to sell to pet distributors, without provision for their highly specialized nutritional needs (primarily formic acid from harvester ants), resulted in certain death for almost all the collected lizards. In 1967, the state of Texas passed protective legislation preventing the collection, exportation, and sale of Phrynosoma, and by the early 1970s, most states enacted similar laws to protect and conserve horned lizards in the US. As recently as the early 2000s, though, the state of Nevada still allowed commercial sale of Phrynosoma species. Despite limited federal protection in Mexico, horned lizards are still offered in Mexican "pet" markets throughout the country.<ref name=Pianka/>

In 2014, the Center for Biological Diversity in Tucson petitioned the Oklahoma Department of Wildlife Conservation to have the Texas horned lizard put on the endangered species list due to the massive decline of its population in Oklahoma, where it was once plentiful. The center said it may later seek protection for the animal on a federal level; it also said that reptiles in general are dying off at up to 10,000 times their historic extinction rate, greatly due to human influences.<ref>Template:Cite news</ref>

Species and subspecies

The following 21 species (listed alphabetically by scientific name) are recognized as being valid by the Reptile Database, three species of which have recognized subspecies:<ref>Template:EMBL genus www.reptile-database.org.</ref>

Image Common name Scientific name Subspecies Distribution
File:Gfp-mexican-west-coast-giant-horned-lizard (crop 1).jpg Giant horned lizard Phrynosoma asio
Template:Small		 southern Mexico
Baur's short-horned lizard Phrynosoma bauri
Template:Small
(disputed, may be conspecific with P. hernandesi)		 United States (southern Wyoming and Nebraska south through eastern Colorado to northern New Mexico)
File:Phrynosoma blainvillii 131129535.jpg San Diego horned lizard or Blainville's horned lizard Phrynosoma blainvillii
Template:Small		 United States (southern and central California), Mexico (northern Baja California)
File:Phrynosoma braconnieri.jpg Short-tailed horned lizard Phrynosoma braconnieri
Template:Small		 Mexico (Puebla and Oaxaca)
File:Phrynosoma hernandesi - Flickr - aspidoscelis (11).jpg Great Plains short-horned lizard Phrynosoma brevirostris
Template:Small
(disputed, may be conspecific with P. hernandesi)		 Canada and the United States
Cedros Island horned lizard Phrynosoma cerroense
Template:Small		 Mexico (Cedros Island)
File:Phrynosoma cornutum - Flickr - aspidoscelis (4).jpg Texas horned lizard Phrynosoma cornutum
Template:Small		 United States (southeast Colorado, central and southern areas of Kansas, central and western areas of Oklahoma and Texas, southeast New Mexico, and extreme southeast Arizona), Mexico (eastern Sonora, most of Chihuahua, northeast Durango, northern Zacatecas and San Luis Potosí, and throughout most of Coahuila, Nuevo León, and Tamaulipas)
File:09-036 Horned Lizard (Phyrnosoma coronatum) (3481417849).jpg Coast horned lizard Phrynosoma coronatum
Template:Small		 Mexico (Baja California Sur)
San Luis Valley short-horned lizard Phrynosoma diminutum
Template:Small
(disputed, may be conspecific with P. hernandesi)		 United States (Colorado)
Ditmars' horned lizard or rock horned lizard Phrynosoma ditmarsi
Template:Small		 Mexico (Sonora), United States (Arizona)
File:Phrynosoma douglasii 4244.JPG Pygmy short-horned lizard Phrynosoma douglasii
Template:Small		 northwestern United States and adjacent southwestern Canada
Sonoran horned lizard, Goode's desert horned lizard Phrynosoma goodei
Template:Small		 United States (Arizona) and Mexico (Sonora)
File:Phrynosoma hernandesi - Flickr - aspidoscelis (11).jpg Greater short-horned lizard Phrynosoma hernandesi
Template:Small		 southwestern United States and northwestern Mexico
File:Flat-Tailed Horned Lizard (5162160076).jpg Flat-tail horned lizard Phrynosoma mcallii
Template:Small		 United States and Mexico
File:Phrynosoma modestum - Flickr - aspidoscelis (18).jpg Roundtail horned lizard Phrynosoma modestum
Template:Small		 United States (Texas, New Mexico eastern Arizona, southeastern Colorado), northcentral Mexico
File:Lagarto Cornudo Camaleón Cornudo Iv (233411137).jpeg Mexican Plateau horned lizard or Chihuahua Desert horned lizard Phrynosoma orbiculare
Template:Small		 Mexico (Chihuahua, Durango, Morelos, Nuevo León, Puebla, and Veracruz)
Desert short-horned lizard Phrynosoma ornatissimum
Template:Small
(disputed, may be conspecific with P. hernandesi)		 Canada and the United States
File:Desert Horned Lizard.jpg Desert horned lizard Phrynosoma platyrhinos
Template:Small		 southern Idaho in the north to northern Mexico
Guerreran horned lizard Phrynosoma sherbrookei
Template:Small		 Mexico
File:Horned lizard 032507 kdh.jpg Regal horned lizard Phrynosoma solare
Template:Small		 Arizona and Mexico
File:Mexican horned lizard, Phrynosoma taurus.jpg Mexican horned lizard Phrynosoma taurus
Template:Small		 Mexico (Guerrero and Puebla)


Note: In the above list, a binomial authority or trinomial authority in parentheses indicates that the species or subspecies was originally described in a genus other than Phrynosoma.

File:Horned lizards.jpg
Comparison of P. modestum and P. platyrhinos

Symbol

Texas designated the Texas horned lizard (Phrynosoma cornutum) as the official state reptile in 1993.<ref>Texas Horned Lizard Template:Webarchive. State Symbols USA. Retrieved on 2016-10-25.</ref> Wyoming’s state reptile is the “Horn Toad”, the greater short-horned lizard (Phrynosoma hernandesi).<ref name="Wyoming 2011">Template:Cite web</ref><ref name="Mason Lee. 2022">Mason Lee. 2022. Wyoming’s surprising state reptile has spikes, shoots blood from eyes—. Barnyards & Backyards. 6-7 pp. University of Wyoming. </ref>

The "TCU Horned Frog" is the mascot of Texas Christian University in Fort Worth, Texas. The "Horned Toad" is also the mascot for Coalinga High School in Coalinga, California. This school is located in Western Central California and its arid region is home to the San Diego Horned Lizard, which is protected. The City of Coalinga hosts an annual "Horned Toad Derby" on Memorial day weekend which features horned toad races, a carnival and parade.

References

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