The characteristics of a species' evolution can be influenced by its mode of sex determination and, indeed, sex determination mechanisms vary widely among eukaryotes. In nonavian reptiles, the sex determination mechanism has historically thought to be binary, determined either by temperature or genetics. In this study, we add to the growing evidence that sex determining mechanisms in reptiles fall along a continuum rather than existing as a mutually exclusive dichotomy. Using qPCR, we demonstrate that a lizard species, Crotaphytus collaris, possesses sex-based gene dosage consistent with the presence of sex microchromosomes, despite the fact that extreme incubation temperatures can influence hatchling sex ratio. Our results indicate that C. collaris might be the first non-Australian species of lizard having a temperature override of genotypic sex determination, and the first species in which sex switches at both high and low temperatures.