Presence of gular and parietal pits in Atretium schistosum (Serpentes, Colubridae), a singular trait not exclusive to psammophine snakes

The sporadic occurrence of localised pits on parietal plates was recently discovered in different colubrid genera of the subfamily Psammophiinae; these were considered to play a role in sensory perception. In the present study, we describe the presence of similar structures in Atretium schistosum, another colubrid snake reportedly not belonging to the Psammophiinae. As this species is suspected of being phylogenetically distantly related to psammophine snakes, some hypotheses are provided to explain (1) the putative function of these pits, (2) their sporadic occurrence, and (3) to suggest when they may have evolved in the colubroid snake clade.