Talia Michelle Lowi-Merri & David C. Evans (2019)
Cranial variation in Gryposaurus and biostratigraphy of hadrosaurines (Ornithischia: Hadrosauridae) from the Dinosaur Park Formation of Alberta, Canada.
Canadian Journal of Earth Sciences (advance online publication)
doi:
https://doi.org/10.1139/cjes-2019-0073https://www.nrcresearchpress.com/doi/abs/10.1139/cjes-2019-0073#.Xa8hO5JKjX4The Dinosaur Park Formation (Campanian) of Alberta documents one of the most diverse assemblages of hadrosaurine dinosaurs. Historically, two species of the genus Gryposaurus have been recognized in the Dinosaur Park Formation, G. notabilisand G. incurvimanus, which are differentiated primarily on their nasal arch morphology. These two species have recently been suggested to represent either variable morphs within G. notabilis (e.g., ontogeny) or two distinct taxa within an evolving Gryposaurus lineage (e.g., anagenesis). These alternative hypotheses have never been adequately tested via detailed morphological comparisons, morphometrics, or biostratigraphy. A geometric morphometric analysis of hadrosaurine skulls from the Dinosaur Park Formation was performed to assess the influence of ontogeny on skull morphology. G. incurvimanus skulls were found to be distinctly smaller, and morphologically divergent from those of G. notabilis, with larger G. notabilis skulls having higher nasal arches set farther back on the skull, a feature commonly seen in adult individuals of other hadrosaurids, such as Brachylophosaurus and lambeosaurines. Stratigraphic data were used to map this morphology through time, to evaluate the anagenesis hypothesis. The stratigraphic distributions of the two species showed considerable overlap, indicating that the sampled individuals lived over a short period of time (< 0.5 mya). Overall, our results suggest that the hypothesis that G. incurvimanus and G. notabilis represent different ontogenetic stages within a single species cannot be rejected. This study improves our understanding of the extent of potential individual variation within a single Gryposaurus species, which can be useful in assessing the validity of other hadrosaurines.