Urosaurus ornatus, commonly known as the ornate tree lizard, is a species of lizard in the family Phrynosomatidae. The species is native to the southwestern United States and northwestern Mexico. The species, which was formerly called simply the "tree lizard", has been used to study physiological changes during the fight-or-flight response as related to stress and aggressive competition. Its life history and costs of reproduction have been documented in field populations in New Mexico and Arizona. This species has been fairly well studied because of its interesting variation in throat color in males (within a population) that can correlate with different reproductive strategies, Appearance The ornate tree lizard may grow to a snout-to-vent length (SVL) of up to . As adults, all males have paired turquoise patches of skin on the abdomen; females lack this abdominal coloration. Male ornate tree lizards are found in a variety of colors. While not all populations contain more than one or two colors, 9 color types have been documented within U. ornatus. A population documented in Verde River, Arizona, has two types of coloration patterns among male tree lizards that account for 45% of all males. The first is characterized by a blue spot in the center of a larger orange patch on the throat fan ("dewlap"). The second has a solid orange throat fan ("dewlap"). The orange-blue males are more aggressive and defend territories that can include up to four females. The orange males have longer, leaner body types and are much less aggressive. Orange males can be nomadic during dry years, and during rainy years tend to occupy small territories. Hierarchies The differences in throat color can impact many different behaviors and create hierarchies within these lizard populations. It is thought that the blue patch on their throats acts as a badge that signals fighting ability and social status across age or sex classes. In most encounters between males with an orange background and blue spot (OB) and males with just the orange background (O), the OB males are almost always dominant. In the case of an interaction between two OB males, the male with the larger blue spot tends to be more dominant. There is a direct correlation between spot presence/size to social status and dominance within the lizard population. Color variation in the throat can also affect reproduction tactics between different males. Males with a throat color that has a