Description of juvenile specimens of Prosaurolophus maximus (Hadrosauridae: Saurolophinae) from the Upper Cretaceous Bearpaw Formation of southern Alberta, Canada, reveals ontogenetic changes in crest morphology
Date
2019-03-19
Journal Title
Journal ISSN
Volume Title
Publisher
Journal of Vertebrate Paleontology (Taylor and Francis)
Abstract
Three juvenile specimens of Prosaurolophus maximus, represented by articulated to disarticulated skeletons,
are the smallest known individuals for the taxon. Cranial anatomy of the juvenile specimens indicates that diagnostic
characters of P. maximus are ontogenetically variable. In the smallest individual, the crest and deeply excavated fossa at the
caudal margin of the circumnarial depression are poorly developed or absent. The crest approaches adult-like morphology
in large juveniles, whereas crest robusticity and the deep excavation of the circumnarial depression occur only in subadult
and adult individuals. The shape of the caudal margin of the circumnarial depression is consistent between juvenile and
adult individuals, potentially making this feature a reliable character for taxonomic identification at younger ontogenetic
stages. The crest of P. maximus grows isometrically during ontogeny, unlike the positive allometric growth of lambeosaurine
hadrosaur crests, suggesting that this taxon may have had soft tissue structures associated with the narial-crest region,
rather than the bony crest itself, selected for sexual display. Recovered from sediments of the Bearpaw Formation
deposited during the Baculites compressus ammonite zone and magnetochrons 33n.3n to 33n.2n, the juvenile specimens are
stratigraphically younger than P. maximus specimens from the Dinosaur Park Formation (Alberta) and contemporaneous
with most specimens from the Two Medicine Formation (Montana), extending the temporal range of the taxon to 75.7–74
Ma. The occurrence of P. maximus in well-drained terrestrial deposits of the Dinosaur Park and Two Medicine formations
and marine sediments of the Bearpaw Formation indicates that this taxon inhabited various paleoenvironments in western
North America.
Description
Keywords
dinosaur, hadrosaur, ontogeny, Bearpaw Formation, Prosaurolophus
Citation
Drysdale, E. T., Therrien, F., Zelenitsky, D. K., Weishampel, D. B., & Evans, D. C. (2018). Description of juvenile specimens of Prosaurolophus maximus (Hadrosauridae: Saurolophinae) from the Upper Cretaceous Bearpaw Formation of southern Alberta, Canada, reveals ontogenetic changes in crest morphology. Journal of Vertebrate Paleontology, 38(6), e1547310. https://doi.org/10.1080/02724634.2018.1547310