Although numerous fossils have been excavated and described from the Upper Cretaceous (Maastrichtian) Lance Formation, eggs and eggshell remains are rare and have yet to be described in detail. Here, we provide the first description of an eggshell found in the Lance Formation in eastern Wyoming. The eggshell can be attributed to the oofamily Ovaloolithidae, and is most comparable to the oogenus Ovaloolithus based on the smooth outer surface, the eggshell thickness, the closely packed shell units, and the presence of two layers. The eggshell can tentatively be ascribed to either ornithopod or non-avian theropod dinosaurs. This new eggshell expands our understanding of the geographical distribution of ovaloolithid ootaxa throughout the uppermost Cretaceous of North America, having been previously described from the Maastrichtian North Horn Formation of Utah.

Key words: Ovaloolithidae, Dinosauria, eggs, Maastrichtian, Lance Formation, Wyoming.

Tom T.P. van der Linden [tppaleo@gmail.com; ORCID: https://orcid.org/0000-0002-7898-3292], Jonathan J.W. Wallaard [curator@oertijdmuseum.nl; ORCID: https://orcid.org/0000-0002-7752-1598], Maarten de Rijke [maarten@oertijdmuseum. nl; ORCID: https://orcid.org/0000-0003-4652-3782], and René H.B. Fraaije [directie@oertijdmuseum.nl; ORCID: https://orcid.org/0000-0002-3465-1093], Oertijdmuseum, Bosscheweg 80, 5283 WB, Boxtel, The Netherlands.