The Sonorini is a diverse assemblage of cryptozoic to fossorial snakes. Molecular and morphological evidence is ambiguous as to whether the tribe is monophyletic or consists of two or more independent clades. Morphological analysis, using Coluber constrictor and Liochlorophis vernalis as outgroups, indicates that the genera Conopsis, Ficimia, Gyalopion, Pseudoficimia, Stenorrhina, and Sympholis form the sister group to Chilomeniscus, Chionactis, and Sonora. This clade, in turn, is sister to Scolecophis and Tantilla. The putative genera Geagras and Tantillita are nested within the Tantilla calamarina and T. taeniata species groups, respectively.Each of the three major clades contains one or more highly fossorial forms that appear to be independently derived. Morphometric and natural history data from museum specimens, field studies, and the literature indicate that taxa with highly fossorial morphologies specialize on buried prey. Sympholis is at least a part-time commensal of leaf-cutting ants that feeds on beetle grubs; Chilomeniscus is a soil burrower that feeds on burrowing roaches and vermiform beetle larvae, whereas other members of the Ficimia and Sonora clades feed on various combinations of arachnids, orthopterans, and beetle grubs. Geagras redimitus, presumably a detritus burrower, feeds on vermiform beetle larvae, whereas Scolecophis and most Tantilla feed on centipedes. At least three other Tantilla species, including T. gracilis, T. relicta, and T. vermiformis, show parallel trends towards miniaturization, fossorial morphology, and diet of insect larvae.