Theropod dinosaurs from the Albian–Cenomanian Wayan Formation of eastern Idaho

Abstract

The record of terrestrial vertebrates in the upper Albian to Cenomanian Wayan Formation of Idaho is sparse, with most fossils recovered belonging to the small orodromine neornithischian Oryctodromeus cubicularis and the maniraptoran ootaxon Macroelongatoolithus carlylei. Here we report on a diversity of theropod forms now recognised from various isolated teeth, vertebrae, eggs and eggshell. Theropods recognised from isolated teeth include a large possible tyrannosauroid, a small tyrannosauroid, dromaeosaurids, and indeterminate theropods. A possible neovenatorid and indeterminate theropods are recognised from isolated vertebrae. A giant oviraptorosaur is indicated by the presence of rare eggs and common eggshell accumulations referred to Macroelongatoolithus. While these remains are admittedly meager, their presence indicates that a substantial diversity of theropods existed in the Albian to Cenomanian environments of southeastern Idaho. The Wayan theropod assemblage is among the most diverse reported for this time period in North America, and represents a transitional assemblage resembling that of the later Late Cretaceous.

Keywords:

• Cretaceous
• Albian
• Cenomanian
• Wayan Formation
• theropod
• Idaho

Acknowledgements

Appreciation is expressed to three anonymous reviewers who improved the quality of this report with their helpful comments and suggestions. Thanks to Angela Milner, Brooks Britt, Denver Fowler, Hans Sues, Phillip Currie and Tom Holtz for their assistance in assessing some of the specimens described here. We thank Jason Moore who discovered the H34D site. Thanks to Robert Simon for his generous personal donation of funds that assisted with travel and collection of specimens from the Robison Bonebed. Appreciation is expressed to Caribou-Targhee National Forest for saving the matrix blocks at the Robison Bonebed (RB) for future work, and to the construction personnel who assisted during initial work at the RB. Holley Flora, Seth Scott and Kelli Sutherland discovered one of the fossils (IMNH 50832) described. Specimens were collected under Caribou-Targhee National Forest paleontology use permits ID34, ID40 and ID40-01. Thanks to Ali Abusaidi for assistance with the permitting process and Mary Thompson of IMNH for access to specimens. Frankie Jackson, Bob Jackson, Joey Stiegler, Darrin Strosnider and Paul Ullmann assisted with excavation of the egg sites. Special thanks to Steve Robison, for discovering some of the localities described here and for his continual support with collection and discovery of specimens. Elise Krumenacker provided assistance at the RB and made her dad proud. Ted Dyman provided geological interpretations at the RB. We express appreciation to Kathleen Ugrin and Advanced Medical Imaging of Bozeman Deaconess Hospital for providing access to their CT scanning equipment and for their assistance with imaging some of the vertebrae described. All specimens are figured courtesy of the Idaho Museum of Natural History and the Paleontology Program of the US Forest Service, Department of Agriculture.