New data on the diversity and abundance of small-bodied ornithopods (Dinosauria, Ornithischia) from the Belly River Group (Campanian) of Alberta

ABSTRACT

Relative to large-bodied dinosaurs, the diversity of small-bodied dinosaurs from the Campanian of North America is poorly understood due to a lack of well-preserved skeletons. We document the first articulated remains, as well as the first cranial bones, of non-iguanodontian ornithopods from the Belly River Group of Alberta. The geologically oldest specimen consists of the posterior half of an articulated skeleton from the middle unit of the Oldman Formation and shares many anatomical features with the contemporaneous Orodromeus makelai and the older Oryctodromeus cubicularis. A second, younger specimen from the upper Oldman Formation is distinct from other ornithopods in having a reduced distal portion of the fibula that is fused to the anterior surface of the tibia; it is designated as the type of a new taxon, Albertadromeus syntarsus, gen. et sp. nov. Numerous isolated elements from small ornithopods from the Dinosaur Park Formation are also identified, but cannot be assigned to the generic level with confidence. Although small-bodied ornithopod material is rare, their known postcranial material outnumbers those of taphonomically equivalent and contemporaneous pachycephalosaurs, which are known to be abundant and diverse due to their robust and frequently recovered cranial domes. These findings suggest considerable undiscovered diversity of small-bodied ornithopods, and highlight biases against the preservation of small taxa in this system.

SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

ACKNOWLEDGMENTS

This research was largely conducted by C.M.B. as part of a M.Sc. degree program at the University of Calgary. W. Sloboda discovered and collected TMP 2008.045.0002, which was subsequently prepared by D. Macleod. TMP 2009.037.0044 was discovered by D.C.E. during the 2010 Southern Alberta Dinosaur Project (SADP) field program and its collection was assisted by P. Bell. I. Morrison prepared much of TMP 2009.037.0044. P. Barrett assisted in the original interpretation of TMP 2009.037.0044. Much of the isolated material from the Belly River Group was discovered and collected by the late E. Nicholls. J. Anderson, C. Boyd, K. Brink, D. Brinkman, N. Campione, K. Chiba, P. Currie, P. Galton, C. Henderson, D. Henderson, D. Larson, N. Longrich, L. O’Brien, R. Scheetz, R. Sissons, D. Tanke, and J. Theodor provided useful discussion and contribution to this project. Comments from P. Barrett and C. Boyd resulted in improvements to the manuscript.

Specimen access and assistance was facilitated by: C. Mehling (AMNH); M. Feuerstack, K. Shepherd, A. McDonald, and E. Ross (CMN); J. Horner and B. Baziak (MOR); V. Schneider (NCSM); P. Barrett, S. Chapman, and S. Maidment (NHMUK); M. Brett-Surman and M. Carrano (USNM); K. Seymour (ROM); B. Strilisky, J. Gardner, D. Brinkman, J. Wilkie, T. Courtenay, and R. Russell (TMP); H. Bryant, T. Tokaryk, and W. Long (RSM); S. Shelton (SDSM); and P. Currie, E. Koppelhus, A. Locock, and J. Glasier (UALVP).

This research was supported by generous funding from: ACCESS, a Queen Elizabeth II Graduate Scholarship, and an Alberta Graduate Student Scholarship all from the Alberta Government; University of Calgary Research Services Travel Grant and Graduate Research Scholarships, Dr. Anthony Russell Distinguished Faculty Achievement Graduate Scholarships in Zoology, Dinosaur Research Institute Student Project Grants, Dinosaur Research Institute Rene Vandervelde SVP Travel Grants, and NSERC CGS Alexander Graham Bell Canada Graduate Scholarship to C.M.B., as well as NSERC Discovery Grants to A.P.R. and D.C.E. The Willi Hennig Society allowed for free access to the program TNT. Field work was funded by the Dinosaur Research Institute, the Royal Ontario Museum, and the Cleveland Museum of Natural History, and was conducted as part of the Southern Alberta Dinosaur Research Project.

Handling editor: Paul Barrett.