Osteology and phylogenetic relationships of the mid-Cretaceous neornithischian dinosaur Oryctodromeus cubicularis Varricchio, 2007

ABSTRACT

The vertebrate assemblages of the Albian to Cenomanian Wayan Formation of southeastern Idaho and southwestern Montana’s coeval Vaughn Member of the Blackleaf Formation are dominated by the small, burrowing orodromine dinosaur Oryctodromeus cubicularis. Here, we describe in detail the osteology of Oryctodromeus based on new specimens from Idaho and Montana that add substantially to the preliminary description of the types from Montana, and provide a suite of additional diagnostic characters for the taxon: ilium with elongate preacetabular process; elongate cervical vertebra centra with an anteroposterior length 1.6 times the dorsoventral height; elongate dorsal vertebra centra with an anteroposterior length 1.4 times the dorsoventral height; more than 55 elongate caudal vertebrae enveloped in hypaxial and epaxial ossified tendons; and a femoral head on an elongate neck—similar to that of Koreanosaurus—projecting from the greater trochanter at about 35°. The tail, comprising two-thirds of the animal’s roughly 3 meters length, and associated tendon sheaths in the axial column indicate greater flexibility than previously supposed for ossified tendons or, alternatively, suggest that the Oryctodromeus burrows had separate, or multiple entrances and exits. The elongated and angled femoral head likely facilitated digging via a braced splayed-leg posture. Our phylogenetic analysis incorporates new characteristics and supports the monophyly of Orodrominae, a clade of neornithischian dinosaurs from the middle to Late Cretaceous of Asia and western North America that utilized burrowing.

DATA AVAILABILITY STATEMENT

The authors confirm that the data supporting the findings of this study are available within the article and the linked supplementary materials.

DISCLOSURE STATEMENT

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

ACKNOWLEDGMENTS

We thank the Jurassic Foundation, the Graduate School of Montana State University, and the always generous R. Simon for funding. L.J.K. thanks committee members D. Bowen, T. Dyman, and J. Horner for their assistance and revisions which improved the quality of this manuscript. Appreciation is expressed to the reviewers and the editors of this manuscript, who patiently and studiously improved the quality of the final product. Thanks to M. Thompson and J. Scannella who allowed access to specimens under their care. A. Abusaidi, S. Robison, and D. Wheeler assisted in the permitting process for collection of specimens from Caribou-Targhee National Forest and B. Beasley permitted access to Beaverhead-Deerlodge National Forest. T. Dyman, A. Ferguson, D. Krumenacker, E. Krumenacker, J. Krumenacker, K. Taddy, and J. Wilson assisted with the collection of Oryctodromeus specimens. B. Robison excelled as a student aid getting copies related to this manuscript for me from the MVMS teachers lounge. E. Krumenacker patiently helped her father check the works cited for this manuscript. This study has been done in memory of Bill Akersten, who exemplified being a great mentor to LK by setting him on the path of science in a kind and supportive manner. Thank you Bill.

AUTHOR CONTRIBUTIONS

LJK wrote the initial and subsequent drafts, gathered and coded the original data, and created and edited the figures as part of his unpublished doctoral dissertation and subsequent revisions. DJV edited the initial draft and provided revisions for the manuscript. CO conducted the phylogenetic analyses and provided additional edits. JDG also conducted phylogenetic analyses, wrote the phylogenetics sections, created supplementary figures, and provided additional edits within the main text. BBB assisted with the original figures and provided subsequent edits. CB assisted with the coding of the characters for the phylogenetic analyses.

SUPPLEMENTARY FILES

Supplementary Data 1: Supplementary Figures S1–S5; descriptions of nexus files for phylogenetic analyses.

Supplementary Data 2: Krumenacker.MrBayes_Boyd.nex; nexus file for the analysis of Boyd’s (2015) original matrix.

Supplementary Data 3: Krumenacker.MrBayes_Trial1.nex; nexus file for the time-calibrated analysis with only the root constrained.

Supplementary Data 4: Krumenacker.MrBayes_Trial2.nex; nexus file for the time-calibrated analysis with Dinosauria and the root constrained.

Supplementary Data 5: Krumenacker.MrBayes_Trial3.nex; nexus file for the time-calibrated analysis with Dinosauria, Ornithischia, and the root constrained.

Supplementary Data 6: Krumenacker.MrBayes_Trimmed.nex; nexus file for the analysis of the reduced matrix.

Supplementary Data 7: Krumenacker.MrBayes_Untrimmed.nex; nexus file for the analysis of the revised Boyd (2015) matrix.