Giant dinosaur eggs occur within the mid-Cretaceous Liangtoutang Formation of the Tiantai basin in Zhejiang Province of southeastern China. The 43 cm × 14.5 cm eggs represent the first discovery of Macroelongatoolithus xixiaensis specimens from the region. The eggshell exhibits variation in surface ornamentation and eggshell thickness, with smoother and thicker eggshell characteristic of the poles. The Tiantai eggs differ from the stratigraphically younger type specimen of Macroelongatoolithus xixiaensis from Henan Province in their mammillary to continuous layer ratio. Three new features potentially useful for phylogenetic analysis and previously unreported in Macroelongatoolithus and other eggs in the oofamily Elongatoolithidae include prismatic columns, tabular structure within the prisms, and “splaying” of the crystals in the upper mammillae that extend into the overlying continuous layer. Microstructural features of the two nearly complete eggs suggest that the specimens are referable to a potentially large theropod dinosaur. Paleogeographic distribution of these large theropod eggs includes the Late Cretaceous Zoumagang Formation of Henan Province and the mid-Cretaceous Liangtoutang Formation of Zhejiang Province in central and southeastern China and possibly the Lower Cretaceous Cedar Mountain Formation and mid-Cretaceous Dakota Formation of Utah, USA.

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