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Abstract
We describe an early juvenile specimen (ZMNH M8812) of Bolong yixianensis from the Yixian Formation (Lower Cretaceous) of Ningcheng County, Nei Mongol, China. The specimen consists of an almost complete skeleton preserved two-dimensionally on a slab. The short and deep skull proportions and unfused neurocentral sutures in most preserved vertebrae suggest that the ZMNH M8812 is a juvenile individual. Osteohistological study confirms a very early developmental stage. The study reveals the ontogenetic changes of Bolong for the first time. The specimen revealed one additional autapomorphy for Bolong yixianensis: the lingual face of the maxillary crown is bounded by thickened mesial and distal margins and bisected by a prominent median principal ridge. The study revealed the following ontogenetic trends of Bolong: increased tooth rows in both maxilla and dentary, increased robustness of the jugal and scapula, the radius and ulna become more robust and shorter relative to the hindlimb and the metatarsals become proportionally shorter. ZMNH M8812 represents the first juvenile non-hadrosaurid iguanodontian specimen described from the Lower Cretaceous of eastern Asia.
Acknowledgements
We are grateful to David Varricchio and Frankie Jackson (Montana State University, USA) for reading the manuscript and offering many valuable suggestions. We thank Yuqing Zhang and Chaohe Yu for preparing the specimen and Dr Junchang Lü (Institute of Geology, Chinese Academy of Geological Sciences, Beijing) for helping in the process of preparation. The thin sections of the femur were made at Museum of the Rockies, Montana. We thank Anusuya Chinsamy-Turan (University of Cape Town, South Africa) for helpful comments in our osteohistology study.