Preliminary reconstructions of nasal chemosensory evolution in Squamata

Squamate reptiles are known for using vomerolfaction, the sense associated with the vomeronasal organs, to detect prey, predators, and conspecifies. By comparison, olfaction has been relatively neglected, yet many squamates have highly developed olfactory systems. Data from the literature were used to make preliminary reconstructions of the evolution of the vomeronasal and olfactory systems in Squamata. Vomerolfaction is highly developed in nearly all squamates, and was enhanced progressively in the common ancestors of Scleroglossa, Autarchoglossa, and Anguimorpha, reaching peaks in two autarchoglossan clades, Varanoidea, and Lacertiformes. Olfaction also improved in the common ancestor of Scleroglossa. Olfactory receptor abundance peaked in Gekkota and Lacertoidea, but declined in Anguimorpha, with some increase in snakes. Five major clades of lizards differ in development of chemical senses. Iguanians have the least developed vomerolfaction and olfaction. Gekkotans and lacertoideans have the greatest olfactory development, with greater vomerolfactory development in Lacertoidea. Scincoideans have intermediate olfaction and vomerolfaction. Anguimorphans have the most specialized vomerolfaction coupled in snakes with apparently greater olfactory powers than in varanids.