We examined museum specimens of the Common Barking Gecko (Ptenopus garrulus) from the Kalahari and Namib Deserts to assess sexual size dimorphism, reproductive status, and diet. Males had significantly wider heads than females of the same body size; however, P. garrulus showed no sexual dimorphism in any other morphological character. The smallest mature male was 36 mm snout–vent length, whereas the smallest female was 31 mm. Peak reproductive activity for both sexes was in September and October. Clutch size was fixed at one large egg (average size = 5.9 × 4.4 mm); all eggs were in the right ovary, but more than one clutch may be laid in a single breeding season. Ptenopus garrulus, when compared with other geckos, produces very large offspring and thereby invest heavily in a single offspring. We recorded 15 arthropod orders in the diet of P. garrulus. Termites dominated their diet both numerically and volumetrically. Males and females ate prey of similar taxa and sizes, suggesting that trophic partitioning is absent. Therefore, the evidence suggests that the evolution of head width differences is driven by male contest competition.