A heretofore unknown teiid lizard, recovered from the Cedar Mountain Formation (Albian–Cenomanian boundary) of Emery County, Utah, is the oldest teiid that is represented by numerous specimens. This new taxon has a heterodont dentition with conical anterior teeth and transversely oriented bicuspid posterior teeth that are distinct from those of Peneteius (Late Cretaceous) and Teius and Dicrodon (Recent). It also shows ontogenetic variation in tooth shape, in which the posterior teeth become more massive and have more transversely expanded crowns, as the individual grows older. Further comparisons and analysis indicate (1) that North American Cretaceous Polyglyphanodontinae (characterized by teeth with transversely-oriented crests) achieved their unusual dental specializations independently from those of analogous modern taxa; (2) that their transverse tooth-cresting resulted from addition of a medial cusp (rather than crown rotation, as previously hypothesized and which apparently is the case for living taxa); and (3) that the species from the Cedar Mountain Formation represents a sister-taxon to other North American polyglyphanodontines Polyglyphanodon, Peneteius and presumably Paraglyphanodon and Dicothodon. The new taxon thus represents an example of the morphologically antecedent dental specializations that culminated in the strikingly specialized dentition of Polyglyphanodon sternbergi.