CRANIOFACIAL ONTOGENY IN LAMBEOSAURINAE AND AN INVESTIGATION OF ANAGENESIS IN THE FOSSIL RECORD

The cranial osteology of Corythosaurus, Hypacrosaurus, and Lambeosaurus are well known; specimens have been collected since the early 20th century, yielding a high sample size from Late Cretaceous North America. This assemblage includes three stratigraphically separate species: C. casuarius (older) and C. intermedius (younger), and L. lambei (older) and L. magnicristatus (younger), representing anagenetic lineages, and H. altispinus and H. stebingeri as well. They provide the opportunity for studying anagenesis through ontogeny. Previous ontogenetic work on lambeosaurines is size-based; however, size is variable, where it does not always represent relative maturity. The primary goals of this project were to (1) obtain a cladistic ontogeny for C. casuarius, C. intermedius, H. altispinus, H. stebingeri and L. lambei, (2) obtain the position of C. intermedius specimens among those of C. casuarius, and (3) obtain the ancestral ontogeny for the clade. Growth series were obtained using a cladistic approach. Hypothetical ontogenetic characters were obtained from the primary literature, two skulls, and a cast of a juvenile skull. Data matrices were constructed in the software program MacClade 4.0; the analyses were run in Phylogenetic Analysis Using Parsimony (PAUP 4.0*). A hierarchical structure was recovered for each analysis. The results include: (1) a hierarchical structure was recovered for each data matrix; (2) for C. casuarius, 11 trees of 61 steps with a CI of 0.84, where the strict consensus tree has 6 growth stages; (3) for C. intermedius, 1 tree of 55 steps with a CI of 0.65, where the tree has 6 growth stages; (4) for a combined Corythosaurus analysis, 7 trees of 113 steps witha CI of 0.58, where the strict consensus tree has 12 growth stages; (5) for L. lambei, 2 trees of 74 steps with a CI of 0.72, where the strict consensus tree has 8 growth stages; (6) for H. altispinus, 3 trees of 31 steps with a CI of 0.90, where the strict consensus tree has 4 growth stages; (7) for H. stebingeri, 3 trees of 34 steps with a CI of 0.88, where the strict consensus tree has 6 growth stages; (8) comparison of the growth stages of C. casuarius and L. lambei ontogenies show three unambiguously optimized ontogenetic characters are seen in the ancestral ontogeny of the clade. For all taxa, it was found that maturity is not strictly congruent with size.