The preserved dentary has small, peg-like teeth, with the underlying jaw bone about four times deeper than the height of each tooth crown. The jaw was originally collected with eleven preserved teeth and two or three more spaces for broken teeth. However, during preparation the front half of the fossil was destroyed, leaving only the rear part of the jaw with five preserved teeth and one or two empty spaces. Up to 20 teeth may have been present in a complete lower jaw. The teeth are positioned apicolingually (slightly inwards of the upper edge of the jaw bone). The penultimate tooth in the back of the jaw has a higher attachment point and its base is cemented to the jaw bone. The jaw as a whole can be characterized as having pleuroacrodont tooth implantation.[2]
Cargninia was originally described as a lepidosaur (crown-group lepidosauromorph), possibly related to the gliding kuehneosaurids.[1] A 2020 redescription later considered it a valid, albeit fragmentary, lepidosauromorph with uncertain relations to other members of the group. Its pleuroacrodont dentition is similar to Gephyrosaurus (a basal rhynchocephalian) and Gueragama (a basal acrodontansquamate), which are each early members of major lepidosaur lineages with acrodont dentition. In the absence of more data, Cargninia's condition is considered to be a case of homoplasy (convergent evolution).[2] Several additional pleuroacrodont jaw fragments are known from Faxinal do Soturno, though a lack of overlap prevents an unambiguous referral to Cargninia.[2]
