Collared Lizard
The Common collared lizard, Oklahoma collared lizard or collared lizard, Crotaphytus collaris, is a North American lizard that can reach a foot (30 cm) long in length (including the tail), with a large head and powerful jaws. They are well known for the ability to run on their hind legs, looking like small dinosaurs. The collared lizard is the "state reptile" of the United States state of Oklahoma, where it is known as the Mountain Boomer. The name "collared lizard" comes from the lizards' distinct coloration, which includes bands of black around the neck and shoulders that look like a collar. It is a member of the collared lizard family.

These reptiles are often tamed and kept as pets. When born in captivity, they are quite docile and tolerant of interaction with humans. They are very active and predatory lizards, requiring a large amount of space to run. They prefer high temperatures, up to 105-110°F (40-43°C) at their basking spot and 80°F (26°C) elsewhere in their habitat during the day. Some collared lizards eat small amounts of fruit or vegetables, but most prefer a diet of insects. They will also consume vertebrate prey, including small mammals and other lizards. Like many reptiles, in captivity they must be provided a diet supplemented with extra calcium and a light source with a UVB radiation to reduce the risk of bone disorders.

The origin of the name "mountain boomer" is not clear, but it may date back to settlers travelling west during the Gold Rush. One theory is that settlers mistook the sound of wind in canyons for the call of an animal in an area where the collared lizard was abundant. In reality, collared lizards are silent.

Like many other lizards, including the frilled lizard and basilisk, collared lizards can run on their hind legs, and are relatively fast sprinters. Record speeds have been around 16 miles/hour (26 km/h), much slower than the world record for lizards (21.5 miles/h or 34.6 km/h) attained by the larger-bodied Costa Rica spiny-tailed iguana, Ctenosaura similis.

Collared lizards in the wild have been the subject of a number of studies of sexual selection. In captivity if two males are placed in the same cage they will fight to the death. This is not only in captivity though for it will fight if any other male is in its presence. Females will not fight though because just like many other animals in the animal kingdom the males fight to get the females attention. Then they will try to kill the other male to win the female over. Males have a blue-green body with a light brown head. Females have a light brown head and body.