Craniomandibular anatomy of a juvenile specimen of Edmontosaurus regalis Lambe, 1917 clarifies issues in ontogeny and biogeography

ABSTRACT

Edmontosaurus regalis is a hadrosaurid represented by abundant fossil material from the late Campanian–early Maastrichtian of what is now Alberta, Canada. Despite its prevalence, juvenile craniomandibular elements of E. regalis are poorly known. A newly collected partial skeleton from the Horseshoe Canyon Formation, UALVP 60425, represents a small saurolophine with a partial skull (skull length ∼500 mm). It can be referred to Edmontosaurini based on the presence of a postorbital fossa and anteroposteriorly long frontals that lack a dorsally oriented nasal contact and contribute significantly to the orbital margin. Despite its small size and presumed immaturity, UALVP 60425 is assigned to E. regalis based on a horizontal shelf on the postorbital process of the jugal. The deep postorbital fossa that, in part, diagnoses E. regalis is acquired during growth. UALVP 60425 shares many features with the Alaskan Prince Creek saurolophine (Ugrunaaluk kuukpikensis); both show consistent anatomical differences in the lacrimal, jugal, and postorbitals from E. annectens throughout their growth series. New data from UALVP 6025 supports referring the Alaskan saurolophine material to Edmontosaurus cf. regalis in the absence of large-sized cranial material from the Prince Creek Formation.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the author(s).

DATA AVAILABILITY STATEMENT

The individual skull bone scans, as well as the assembled skull, are available as mesh files at https://www.morphosource.org/projects/000606391?locale=en.

ACKNOWLEDGMENTS

UALVP 60425 was nicknamed “Gary” after The Far Side comic artist G. Larson, for its location on the “far side” of the UALVP Morrin fieldwork study area. The land where the specimen was collected is the traditional home of the Kanai (Blood), Tsuu T’ina (Sacree), Siksika (Blackfoot), Piikani (Peigan), and Nakoda (Stoney) First Nations, and the Métis Nation. The current landowners in the area are Lyle Hiller and his family, and we would like to thank them for access to the site. We wish to thank the numerous volunteers who, in addition to the listed authors, aided the excavation and preparation of the cranium of UALVP 60425, particularly Khoi Nguyen for finishing preparation of the cranium of UALVP 60425 and Y-Y. Wang for his guidance in surface scanning UALVP 60425 and 47919. J. Mallon, A. Tirabasso, N. Rybczynski, C. Kum, and A. McDonald at the Canadian Museum of Nature supplied surface scans of CMN 2289. We thank H. Gibbins, C. Sullivan, R. Sissons, and C. Coy (University of Alberta), K. Seymour (Royal Ontario Museum), S. En Pan (Canadian Museum of Nature), N. Smith, and S. Abramowicz (Los Angeles County Natural History Museum), and P. Druckenmiller and Z. Perry (University of Alaska) for specimen resources. We are indebted to N. Campione, D. Evans, M. Wosik, J. Napoli, A. Ruebenstahl, and R. Takasaki for discussions that improved the manuscript.

AUTHOR CONTRIBUTIONS

HSS led the study. PJC provided project administration. HSS and GFF conceptualized the study and wrote the original draft. HSS, CWG, and GFF created figures. MJP, APM, PCJ, and GFF supervised the project. HSS, MJP, ADD, MMR, APM, CWG, and GFF played principal roles in the excavation and preparation of UALVP 60425. All authors reviewed and edited the manuscript.

SUPPLEMENTARY FILES

Sharpeetal_Supplementary_Data.docx: measurements and statistics for maxillary regression.