font settings

Font Size: Large | Normal | Small
Font Face: Verdana | Geneva | Georgia

Phrynosoma

(Genus)

Overview

[ Back to top ]

Horned lizards (Phrynosoma) are a genus of lizards which are the type genus of the family Phrynosomatidae. 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 15 species of horned lizards in North America, eight 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).

[ Back to top ]

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

Protection against predation

Coast horned lizard (Phrynosoma coronatum) after squirting blood from its eye to protect itself

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 more difficult to swallow. At least four species are also able to squirt an aimed stream of blood (see Autohaemorrhaging) from the corners of the eyes for a distance of up to five feet.[1][2][3] 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, 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 the lizard.

Species and subspecies

[ Back to top ]
  • Phrynosoma douglassi brachycercum H.M. Smith, 1942
  • Phrynosoma douglasii douglasii (Bell, 1828)
Comparison of P. modestum and P. platyrhinos
  • Phrynosoma orbiculare boucardii (Dum?ril & Bocourt, 1870)
  • Phrynosoma orbiculare bradti Horowitz, 1955
  • Phrynosoma orbiculare orbiculare (Linnaeus, 1789)
  • Phrynosoma orbiculare orinetale Horowitz, 1955
  • Phrynosoma orbiculare cortezii (Dum?ril & Bocourt, 1870)
  • Phrynosoma orbiculare dugesii (Dum?ril & Bocourt, 1870)
  • 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

Symbol

[ Back to top ]

The genus of horned lizards is the official state reptile of Wyoming.[4]

The Texas horned lizard is the state reptile of Texas and the "horned frog" is the mascot of Texas Christian University in Fort Worth, Texas.

its eye to protect itself

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 more difficult to swallow. At least four species are also able to squirt an aimed stream of blood (see Autohaemorrhaging) from the corners of the eyes for a distance of up to five feet.[1][2][3] 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, 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 the lizard.

Species and subspecies

[ Back to top ]
Comparison of P. modestum and P. platyrhinos

Symbol

[ Back to top ]

The genus of horned lizards is the official state reptile of Wyoming.[4]

The Texas horned lizard is the state reptile of Texas and the "horned frog" is the mascot of Texas Christian University in Fort Worth, Texas.

Notes

[ Back to top ]
  1. ^ Middendorf III, G.A.; Sherbrooke, W.C. & Braun, E.J. (2001): Comparison of Blood Squirted from the Circumorbital Sinus and Systemic Blood in a Horned Lizard, Phrynosoma cornutum. The Southwestern Naturalist., 46(3): 384-387.
  2. ^ Sherbrooke, W.C. & Middendorf III, G.A. (2001): Blood-Squirting Variability in Horned Lizards (Phrynosoma). Copeia., 2001(4): 1114-1122.
  3. ^ Sherbrooke, W.C. & Middendorf III, G.A. (2004): Responses of Kit Foxes (Vulpes macrotis) to Antipredator Blood-Squirting and Blood of Texas Horned Lizards (Phrynosoma cornutum). Copeia., 2004(3): 652-658.
  4. ^ "State symbols". Wyoming Secretary of State's Office. 2011. http://soswy.state.wy.us/SecretaryDesk/StateInfo_Symbols.aspx. Retrieved January 22, 2011. 

External links

[ Back to top ]

Taxonomy

[ Back to top ]

The Genus Phrynosoma is further organized into finer groupings including:

References

[ Back to top ]

Footnotes

[ Back to top ]
  1. ^ Middendorf III, G.A.; Sherbrooke, W.C. & Braun, E.J. (2001): Comparison of Blood Squirted from the Circumorbital Sinus and Systemic Blood in a Horned Lizard, Phrynosoma cornutum. The Southwestern Naturalist., 46(3): 384-387.
  2. ^ Sherbrooke, W.C. & Middendorf III, G.A. (2001): Blood-Squirting Variability in Horned Lizards (Phrynosoma). Copeia., 2001(4): 1114-1122.
  3. ^ Sherbrooke, W.C. & Middendorf III, G.A. (2004): Responses of Kit Foxes (Vulpes macrotis) to Antipredator Blood-Squirting and Blood of Texas Horned Lizards (Phrynosoma cornutum). Copeia., 2004(3): 652-658.
  4. ^ "State symbols". Wyoming Secretary of State's Office. 2011. http://soswy.state.wy.us/SecretaryDesk/StateInfo_Symbols.aspx. Retrieved January 22, 2011. 

Sources

[ Back to top ]
Last Revised: August 24, 2012
2012/08/24 16:24:08