The cranial osteology of Corythosaurus is well known; specimens have been collected since the early 20th century, resulting in a high sample size (21 specimens) from the Dinosaur Park Formation (Late Campanian, Cretaceous) in Alberta, Canada. This assemblage includes two stratigraphically separate species,  C. casuarius (older) and C. intermedius (younger), representing an anagenetic lineage. It provides the opportunity for studying anagenesis through ontogeny. The sample includes juveniles, subadults, and adults. Previous ontogenetic work on Corythosaurus is size-based, however, size is variable, where it does not always represent relative maturity. The primary goals of this study were to (1) obtain a cladistic ontogeny for C. casuarius and C. intermedius, (2) compare the ontogenies to identify interspecific differences, and (3) obtain the position of C. intermedius specimens among those of C. casuarius.  Hypothetical ontogenetic characters were obtained from the primary literature, an adult C. casuarius skull, and a cast of a juvenile C. casuarius skull. Growth series were obtained using a cladistic approach. Data matrices were constructed in the software program MacClade 4.0; the analyses were run in Phylogenetic Analysis Using Parsimony (PAUP 4.0*). The results of the analyses showed that in the combined analysis, C. intermedius specimens were recovered within the subadult growth stage of C. casuarius. Therefore, the pattern of anagenesis, in this case, shows two species that are indistinguishable from growth stages.