An oviraptorosaur adult-egg association from the Cretaceous of Jiangxi Province, China

ABSTRACT

With abundant well-preserved clutches and several adult-clutch associations, oviraptorids provide some of the most detailed information on reproduction for dinosaurs. Here, we describe an oviraptorosaur closely associated with two eggs from the Upper Cretaceous Nanxiong Formation of Jiangxi Province, China, and discuss its implications for various reproductive hypotheses. The specimen consists of a partial skeleton (gastralia, pelvis, portions of both hind limbs, and tail), with one egg within the pelvic canal and the other just posterior to it, ventral to the anterior caudal vertebrae. Several geopetal features indicate that the individual came to rest on its left side, with the eggs likely extruded during buildup of abdominal gases during decomposition. Similarity of pubis, caudal vertebrae, and pes dimensions to recently described material from the formation, e.g., Tongtianlong and Jiangxisaurus, suggests oviraptorid affinities. The specimen provides additional association of elongatoolithid eggs and the oogenus Macroolithus with oviraptorosaurs and further evidence for monoautochronic ovulation, i.e., iterative laying of two eggs at daily or greater intervals. With each egg 36–48% the size predicted for a modern bird of the same adult mass, total egg production would be slightly lower to similar between this non-avian maniraptoran and Neornithes. Histological tissues and open neurocentral sutures indicate that this reproductively active individual was several years old but still growing at the time of death, a pattern observed in other non-avian maniraptorans. The complete absence of medullary bone in this egg-bearing individual may challenge the identification of this tissue in other dinosaurs more distantly related to birds.

ACKNOWLEDGMENTS

We thank the Zhejiang Museum of Natural History staff, especially W. Zheng, X. Li, and S. Gu, for their assistance and congeniality and F. Jackson for her great input on the eggshell and for manuscript editing. We thank S. Werning and L. Chang for important assistance and comments, T. Imai and W. Zheng for timely assistance with measurements, and M. Norell and the American Museum of Natural History for access to Mongolian specimens. Discussions with D. J. Simon and D. Barta improved the manuscript. National Natural Science Foundation of China grant no. 41602019 and the State Key Laboratory of Palaeobiology and Stratigraphy (Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences) grant no. 163120 to X. Jin; National Science Foundation EAR grant no. 847777 to D.J.V.; National Geographic Grant no. 8752-10 to D.J.V., X.J., and F. Jackson; and a Doris O. and Samuel P. Welles Research Fund grant to A. Poust provided funding. Finally, we thank T.-R. Yang and D. J. Simon and editor L. Zanno for their careful reviews.