Fig. 1. (A) Phylogenetic relationships and geographic distribution of viper taxa used in this study (modified from Parkinson et al., 2002) and presence (+) or absence (-) of behavioral thermoregulation mediated by thermal radiation cues. Genera in bold indicate use in the present study, with Bothrops group A containing B. alternatus. The asterisk denotes the origin of the facial pit. Phylogenetic relationships of the genera enclosed by the broken box are shown in greater detail in B. (B) Phylogenetic relationships of North American pitvipers used in the present study (genera Agkistrodon, Crotalus and Sistrurus; modified from LaDuc, 2003) and presence of behavioral thermoregulation mediated by thermal radiation cues (+).