RESUMEN
The genus Thamnodynastes is comprised of 19 valid species distributed throughout South America. Thamnodynastes pallidus is associated with the Amazon region and the Atlantic forest of northeastern Brazil, exhibiting a disjunct distribution. The characters employed in the definition of this species are controversial, and its morphological variation is poorly known. Some authors do not consider its distribution in the Atlantic Forest, attributing these specimens to T. almae. This study aims to compare the Amazonian and the Atlantic populations of T. pallidus by performing an analysis of morphological (colouration, morphometry, pholidosis and hemipenial morphology) and geographical variations. We examined 70 specimens of T. pallidus from the Atlantic Forest, and 61 from the Amazon Forest. A logistic regression selected the number of infralabials, number of subcaudals, and snout length as the only predictors that could discriminate the two populations. The distribution model shows regions with higher climatic suitability for T. pallidus spread across the Amazon basin and the Atlantic Forest. We provide sufficient evidence to characterise T. pallidus, and differentiate it from its congeners. Although we demonstrate the occurrence of variation with respect to some meristic and hemipenial characters between and within each population, we conclude that these variations are not sufficient to recognise them as distinct species