The Evolution of the Tongue of Snakes, and its Bearing on Snake Origins

TLDR: The form and texture of the tongue has long been one of the major bases for the classification of lizards, as evidenced by such herpetological catalogues as de Rooij (1915) that base the “synopsis of families” principally on the tongue.

Abstract: The form and texture of the tongue has long been one of the major bases for the classification of lizards, as evidenced by such herpetological catalogues as de Rooij (1915) that base the “synopsis of families” principally on the tongue, and by the “-gjossa” names for higher groups of lizards in the older literature (e.g., Pachyglossa, Leptoglossa, Thecaglossa, Diploglossa, all used by Cope, 1900, but taken by him from earlier authors). I can find no case where a lizard was referred to a particular group on the basis of tongue structure but subsequently found, from other evidence, to be unrelated. On the other hand, in two cases families of lizards have been referred to higher groups against the evidence of the tongue, and subsequent study of the osteology has shown such reference to be in error: the Pygopodidae were referred by Camp (1923) to the same group as that containing Anguidae, Xenosauridae, Anniellidae, Helodermatidae, and Varani-dae, in spite of a very different tongue; but McDowell and Bogert (1954) and Underwood (1957) showed that the Pygopodidae are most closely related to the Gekkonidae, with which they agree in tongue structure as well as many other features.