Horned lizard

From Wikipedia, the free encyclopedia

 This article needs additional citations for verification.
Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (July 2007)
Horned Lizards
Short-horned Lizard
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Order: Squamata
Family: Phrynosomatidae
Genus: Phrynosoma
Wiegmann, 1828
Species

See text.

Horned lizards (Phrynosoma) are a genus of the Phrynosomatidae family of lizards. The horned lizard is popularly called a "horned toad," "horny toad", or "horned frog," but it is neither a toad nor a frog. The popular names come from the lizard's rounded body and blunt snout, which make it resemble a toad or frog. (Phrynosoma literally means "toad-bodied.") The spines on its back and sides are made from modified scales, whereas the horns on the heads are true horns (i.e. they have a bony core). There are 14 species of horned lizards in North America, 8 of which are native to the United States. The largest-bodied and most widely distributed of the U.S. species is the Texas horned lizard (P. cornutum).

Contents

[edit] Description

Horned lizards are morphologically similar to the Australian thorny devil ({{}}Moloch horridus), but are only distantly related. They also have other unique similarities, such as being sit-and-wait predators and preying upon ants, and so the two species are considered a great example of convergent evolution.

[edit] Protection against predation

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 and hope 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 body to cause it to look more horny, making it appear larger and more difficult to swallow. At least four species are also able to squirt an aimed stream of blood from the corners of the eyes for a distance of up to 3 feet. 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. To avoid being picked up by the head or neck, horned lizards duck or elevate their head and orient their 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 that the predator cannot easily get its lower jaw underneath the lizard.

[edit] Diet and decline

The diet of most horned lizards species varies from 60-90% harvester ant of the genus Pogonomyrmex, though they are opportunistic and supplement these with termites, beetles, grasshoppers and other small insects.

In California, Texas, and other states, horned lizards are considered threatened and given state protection, though none are on the federal endangered species list. The Texas horned lizard has declined in about 30% of its range, though there is some indication it may be making a comeback. Some California species are also in decline. The decline is usually blamed on development/destruction of habitat, the spread of non-native South American ants which compete and war with the harvester ant, and the overuse of pesticides which kill harvester ants. In California, the introduced species is the Argentine ant. In Texas, it is the Argentine ant and the Brazilian fire ant. Both species are highly aggressive and fiercely territorial, and prey on harvester ant queens, destroying the horned lizard's principal source of food.

[edit] In culture

Some Native American peoples regarded horned lizards as sacred. The animal is a common motif in the art of many Native Americans in the Southwestern U.S. and in Mexico. In the Clint Eastwood film The Outlaw Josey Wales, the character played by Chief Dan George decides to go to Mexico based on signs given him by a horned toad.

The horned lizard is the state reptile of both Texas and Wyoming, and as the "horned frog," is the mascot of Texas Christian University (TCU).

[edit] Species

  • Cape Horned Lizard, Phrynosoma coronatum coronatum (Blainville, 1835)
  • San Diego Horned Lizard, Phrynosoma coronatum blainvillii (Gray, 1839)
  • California Horned Lizard, Phrynosoma coronatum frontale (Van Denburgh, 1894)
  • Central Peninsular Horned Lizard, Phrynosoma coronatum jamesi (Schmidt, 1922)
  • Northern Peninsular Horned Lizard, Phrynosoma coronatum schmidti (Barbour, 1921)
  • Phrynosoma douglassi brachycercum (Smith, 1942)
  • Phrynosoma douglasii douglasii (Bell, 1828)
Comparison of P. modestum and P. platyrhinos
Comparison of P. modestum and P. platyrhinos
  • Southern Desert Horned Lizard, Phrynosoma platyrhinos calidiarum (Cope, 1896)
  • Northern Desert Horned Lizard, Phrynosoma platyrhinos platyrhinos (Girard, 1852)
  • Sonoran Horned Lizard, Phrynosoma platyrhinos goodei (Stejneger, 1893)
  • Regal Horned Lizard, Phrynosoma solare (Gray, 1845)
  • Mexican Horned Lizard, Phrynosoma taurus (Dugés, 1873)
  • Gulf Coast Horned Lizard, Phrynosoma wigginsi (Montanucci, 2004)

[edit] External links