Avian eggs from the Eocene Willwood and Chadron formations of Wyoming and Nebraska

Partial eggs from the Eocene Willwood Formation of Wyoming contain unidentifiable embryonic remains; the eggs are referable to a theropod on the basis of their structural layering of calcite and to an avian theropod because of their Eocene age. We assign the specimens to the oofamily Medioolithidae as Microolithus wilsoni, oogen. et oosp. nov., on the basis of the following unique combination of characters: 600-µm-thick eggshell composed of...