We report characteristics of a previously unknown population of Ambystoma tigrinum mavortium (barred tiger salamander) from eastern South Dakota, a location that extends the formerly known range of this subspecies about 150 km north. This population contains paedotypic animals and a small percentage of cannibal morphs. At least one cannibal morph was paedotypic. The vomerine tooth hypertrophy characteristic of cannibal morphs described here differs from the cannibal morph A. t. tigrinum from nearby (about 160 km) northwestern Iowa; in particular the pair of caudolateral tooth ridges has smaller teeth in individuals from the A. t. mavortium population. The study wetland is located near the convergence of four recognized (pending revision) tiger salamander subspecies (A. t. diaboli and A. t. melanosticum in addition to A. t. mavortium and A. t. tigrinum), making it an excellent region to examine subspecific morphological features in light of shared ecological factors. We suggest creating a formal nomenclatural distinction between cannibal morph larval phenotypes and cannibal morph paedotypic phenotypes.