Reconstruction of the forelimb musculature of the Cretaceous ornithopod dinosaur Oryctodromeus cubicularis: implications for digging

ABSTRACT

Taphonomic and morphological evidence suggests that Oryctodromeus cubicularis, a basal ornithopod dinosaur from the mid-Cretaceous of Montana, constructed burrows by digging with its forelimbs. Reconstruction of the forelimb musculature of Oryctodromeus was carried out using the extant phylogenetic bracket method, with crocodilians and ratites as the extant analogues, aided by the presence of osteological correlates in Oryctodromeus and other ornithopods. Although reconstructions directly from the extant phylogenetic bracket are relatively conservative, the reconstruction elucidates several potential features related to burrowing. The prominent muscle groups used in burrowing in mammals are the deltoideus scapularis, teres major, latissimus dorsi, and triceps longus. In Oryctodromeus, the deltoideus scapularis, and equivocally the teres major, has broad origin on the strongly posteroventrally expanded distal scapular blade. Neither the origin of the deltoideus scapularis nor that of the teres major produces osteological correlates in extant taxa or Oryctodromeus; however, the ventrally expanded posterior scapular blade would have increased attachment area for the origin of these muscle groups. The presence of the latissimus dorsi is supported by the extant phylogenetic bracket but produces no osteological correlates in Oryctodromeus. The triceps longus originates posterior to the glenoid and inserts on the ulna. Due to the proximity of the triceps longus origin to the glenoid, the triceps longus likely did not provide strong muscle action. Because many mammals and reptiles produce burrows without any morphological specialization, the limited specializations of the deltoideus scapularis and potentially the teres major sufficiently support burrowing capabilities in Oryctodromeus.

Citation for this article: Fearon, J. L., and D. J. Varricchio. 2016. Reconstruction of the forelimb musculature of the Cretaceous ornithopod dinosaur Oryctodromeus cubicularis: implications for digging. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1078341.

ACKNOWLEDGMENTS

We thank the Jurassic Foundation, Sigma Xi, and Montana State University Department of Earth Sciences for providing funding for this project. Many thanks to J. Horner and S. Cherry, as well as D. Barta, D. Fowler, E. Fowler, S. Oser, A. Poust, J. Scannella, D. J. Simon, and C. Woodruff, and the other current and former members of MSU's Dead Lizard Society for all the support and discussion.