Fossil egg and eggshells from the Upper Cretaceous Hell Creek Formation, Montana

ABSTRACT

Despite over a hundred years of intense paleontological exploration, the terrestrial rocks of the Upper Cretaceous (Maastrichtian) Hell Creek Formation of eastern Montana are remarkable for the absence of fossil eggs. Here, we describe the first fossil egg and additional eggshell fragments from the formation. The two-layered structure of the smooth 1600-µm-thick eggshell of Belonoolithus garbani, oogen. et oosp. nov., permits assignment of the 6 cm × 8 cm egg to Theropoda. Additional theropod eggshells, Dimorphoolithus bennetti, oogen. et oosp. nov., closely resemble Tubercuoolithus choteauensis (incertae sedis) from the Campanian Two Medicine Formation of Montana, differing only in ornamentation. Therefore, we establish Tubercuoolithidae, oofam. nov., to accommodate both eggshell types. Other eggshell types include two varieties of Spheroolithus, as well as Testudoolithus and Krokolithes. Whereas B. garbani and D. bennetti are unique to the Hell Creek Formation, the other three oogenera also occur in the stratigraphically older Two Medicine and Judith River formations of Montana, and the Oldman Formation of southern Alberta, Canada.

Citation for this article: Jackson, F. D., and D. J. Varricchio. 2016. Fossil egg and eggshells from the Upper Cretaceous Hell Creek Formation, Montana. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1185432.

ACKNOWLEDGMENTS

Research was supported in part by National Science Foundation grant 0847777 (EAR) to D. Varricchio. We acknowledge the Department of Earth Sciences and the Imaging and Chemical Analysis Laboratory (ICAL), both at Montana State University, for use of facilities. Technical support was generously provided by A. Moore-Nall. John Horner allowed use of the Gabriel Laboratory for Cellular and Molecular Paleontology at the Museum of the Rockies. We thank B. Zorigt for Russian translation of articles, D. Lawver and J. Schmitt for editorial comments and helpful suggestions that improved the manuscript, and W. Clemens for providing background information about the egg locality. G. Bishop dedicated hours to sorting specimens, and D. Barta provided helpful discussion of eggshell features and thin sections of Oblongoolithus eggshell fragments used for comparison. Finally, we especially thank G. Bennett, M. Goodwin, and M. Martell for providing the specimens examined in this study.