Arizonasaurus (Arizona lizard) is a rauisuchian from Middle Triassic Arizona. It was not very large for a rauisuchian, only reaching about 3 meters long, but it has a unique attribute. Two specimens have been found, one of them nearly complete.
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Like Spinosaurus, Ctenosauriscus, Dimetrodon, Edaphosaurus, and Platyhystrix, Arizonasaurus has a unique set of bones along its spine to create a sail despite not being closely related to any of these, suggesting convergent evolution. So far, the purpose of these sails is unknown, although considering the warm environment of the Triassic, they were most likely used for thermoregulation, which was important for animals living in such an environment.
Arizonasaurus likely lived alongside Coelophysis, and competed heavily with these early dinosaurs. It was one of the first rauisuchians to go extinct, likely because even larger rauisuchians like Saurosuchus proved to be too much competition.