The Phrynosomatidae are a diverse family of lizards, 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 lizards prefer rocky deserts or even relatively moist forest edges, and the short-horned lizard lives in prairie or sagebrush environments. The group includes both egg-laying and viviparous species, with the latter being more common in species living at high elevations.
The 136 species are organised into 10 genera in this family.
- Callisaurus Blainville, 1835 – zebra-tailed lizards
- Cophosaurus Troschel, 1852 – greater earless lizards
- Holbrookia Girard, 1851 – earless lizards
- Petrosaurus Boulenger, 1885 – California rock lizards
- Phrynosoma Wiegmann, 1828 – horned lizards
- Sator Dickerson, 1919 – sators
- Sceloporus Wiegmann, 1828 – spiny lizards
- Uma Baird, 1859 – fringe-toed lizards
- Urosaurus Hallowell, 1854 – tree and brush lizards
- Uta Baird & Girard, 1852 – side-blotched lizards
Earless lizards are two genera of small lizards native to the semi-arid and grassland habitats of the southwestern United States and Mexico. The genus Cophosaurus and the genus Holbrookia are both characterized by having no external ear openings, presumably to prevent sand from entering the body as they dig.
Earless lizards have a peculiar defense mechanism which is coupled to their cold-blooded life style. They have a small opening on the top of their head called a 'blood sinus' which helps the lizard to gain heat quickly during daytime. However the blood can also be channelized to the eyes of the lizard when a predator looms close by, efficiently spitting  the blood onto the predator giving it enough time to escape.
Earless lizards are found from the southwestern and central United States, in the states of Texas, Arizona, New Mexico, Utah, Colorado, Kansas, Oklahoma, and as far north as Nebraska, South Dakota, and Wyoming. They are also found in Mexico, in the states of Sonora, Chihuahua, Coahuila, Sinaloa, Durango, Zacatecas, San Luis Potosi, Nuevo Leon, Tamaulipas and Veracruz.
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