The easternmost occurrence of Saurornitholestes from the Judith River Formation, Montana, indicates broad biogeographic distribution of Saurornitholestes in the Western Interior of North America

ABSTRACT

Small-bodied dromaeosaurid and troodontid theropod dinosaurs are present in most of the terrestrial Late Cretaceous formations of the North American Western Interior, but are represented predominantly by shed teeth and more rarely by isolated skeletal elements and associated skeletons. The eudromaeosaurian dromaeosaurid Saurornitholestes is among the most commonly recovered small theropods from North America, known from abundant shed teeth, isolated cranial and postcranial elements, and several partial or near-complete skeletons from the Campanian aged Two Medicine Formation of Montana and the Dinosaur Park Formation of Alberta. Conversely, few Saurornitholestes specimens beyond shed teeth have been recovered from temporally equivalent units of the Judith River Formation of Montana. This study reports the first cranial material, a near-complete frontal, referable to Saurornitholestes from the Judith River Formation of Montana. This specimen is the easternmost occurrence of this taxon and was recovered approximately 400 km east of the localities which have produced referred Saurornitholestes specimens in the Two Medicine Formation, proximal to the Cordilleran thrust front. As such, this new specimen indicates that Saurornitholestes was biogeographically widespread and occupied both inland and coastal environments across the northern portions of the Late Cretaceous Western Interior of North America.

KEYWORDS:

• Dromaeosauridae
• Judith River Formation
• biogeography

Acknowledgments

We thank G. Funston, M. Powers, and P. Currie for identification discussion. Thanks to D. Varricchio for discussion of the Two Medicine Formation Saurornitholestes specimens. Fieldwork funding was provided by the City of Dickinson. BDM 005 was collected from U.S. public lands administered by the Bureau of Land Management under surface collecting permit MTM 108829 issued to DF. We thank the editor Dr. Gareth Dyke and two anonymous reviewers for helpful comments that improved the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.