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Abstract
Numerous discoveries in the Tiantai basin of Zhejiang Province, China, enrich our understanding of the parataxonomy, paleobiology and taphonomic histories of fossil eggs from a diverse array of Cretaceous oofamilies. We describe the most abundant of these egg types catalogued in the Zhejiang Museum of Natural History, Spheroolithus cf. zhangtoucaoensis (oofamily Spheroolithidae). Scanning electron microscopy, here utilised for the first time on Spheroolithus eggs from Tiantai, and petrographic microscopy reveal 0.81–1.37-mm thick eggshell composed of a single structural layer of calcite with slightly flaring shell units, irregular pores, horizontal accretion lines and a sweeping extinction pattern under crossed polars. This contradicts previous reports of the presence of two structural layers in Tiantai Spheroolithus. Clutches consist of 2–13 eggs arranged in an irregular, single-layered pattern. As these eggs are among the oldest Asian examples of Spheroolithus currently known, they may shed light on the early evolution of this oogenus. This study establishes the definitive presence of the Spheroolithidae in the Tiantai basin, contra recent reports, and provides the framework for ongoing examination of egg diversity and taphonomy in the Tiantai basin.
Acknowledgements
Funding for this study was provided by National Science Foundation IRES Grant No. 0854412 to F. Jackson and D. Varricchio, National Geographic Grant No. 8752-10 to D. Varricchio, X. Jin and F. Jackson and a Montana State University Undergraduate Scholars Programme grant to D. Barta, C. Bury, J. Croghan and J. Drost. The authors thank R. Avci for use of the MSU Imaging and Chemical Analysis Laboratory and D. Mogk for access to and expertise in analytical techniques. They thank J. Horner for use of the Gabriel Laboratory for Cellular and Molecular Paleontology in the Paleontology Department of the Museum of the Rockies. They thank M. Kundrát (Uppsala University) and K. Chin (University of Colorado Boulder) for their loans of therizinosauroid eggshell and thin sections. J. Borkowski provided helpful discussion about egg size classes. E. Freedman Fowler shared knowledge of hadrosaurids. A. Ayre, T. Bridges, C. Bury, N. Carroll, J. Drost, C. Heck, C. Lorang, P. Madison, A. Moore-Nall, H. Susorney, H. Wilson and W. Zheng contributed much data and discussion. S. Gu, X. Li and other ZMNH staff provided assistance with travel and fieldwork logistics and specimen access. T. Imai, D. Lawver, S. Oser and D. Simon provided helpful critiques of an earlier draft of this manuscript. They also thank O. Wings and M. Moreno-Azanza for thorough reviews that improved the final manuscript.