The first dinosaur egg from the Lower Cretaceous of Western Siberia, Russia

<p>The Lower Cretaceous Ilek Formation in Western Siberia (Russia) has yielded various vertebrate fossils, including skeletal remains of dinosaurs. Here we report on a fragmentary theropod egg from the vertebrate locality Shestakovo 3 of the Ilek Formation in Kemerovo Province. We assign the specimen to the oogenus <i>Prismatoolithus</i> (oofamily Prismatoolithidae) as <i>Prismatoolithus ilekensis</i> oosp. nov., on the basis of the following unique combination of characters: ovoid-shaped egg; thin eggshell 300–330 μm thick; angustiprismatic morphotype; eggshell with three different layers; gradual transition between mammillary layer and prismatic layer; abrupt contact between prismatic layer and external layer; mammillary layer to prismatic layer to external layer thickness ratio is 1:3:0.6; prismatic layer with ill-defined squamatic texture; angusticanaliculate pore system; and smooth outer surface. Like other Early Creataceous <i>Prismatoolithus</i>, the egg of <i>Prismatoolithus ilekensis</i> oosp. nov. was laid by a small bodied theropod dinosaur (troodontid or primitive bird) and this taxonomic attribution is supported by results of our phylogenetic analysis. <i>Prismatoolithus ilekensis</i> oosp. nov. is the first Early Cretaceous ootaxon from Russia.</p> <p></p>