Oviraptorosaurs, a group of non-avian theropod dinosaurs from the Cretaceous of Asia and North America, left behind the most abundant and informative fossil evidence of dinosaur reproductive biology. Previous studies had suggested that oviraptorosaur reproductive biology represents an intermediate stage and exhibited unique modern avian traits. For instance, the adult-associated clutches were predominantly considered as evidence for brooding/thermoregulatory contact incubation (TCI) behaviors, whereas the hypotheses of laying or protection were neglected. Despite numerous oviraptorid egg clutches uncovered from China and Mongolia, their nest architecture and clutch arrangement were rarely investigated in detail. Here we present a comprehensive reconstruction of an oviraptorid clutch based on five new oviraptorid clutches from Jiangxi Province, China. A detailed examination of the new clutches reveals a partially-open oviraptorid nest that contains 3–4 rings of paired eggs (more than 15 pairs total) whose blunt end points toward the center devoid of eggs at an angle of 35–40°. Our detailed three-dimensional reconstruction indicates that the oviraptorid clutch has a unique architecture unknown from extant bird clutches, implying an apomorphic nesting mode. Such a unique nest architecture further contradicts the TCI hypothesis in oviraptorids, hindering sufficient heat transfer to the inner (lower) ring(s) of eggs. Moreover, the size of the new oviraptorid clutches (>30 eggs) is significantly larger than that of the adult-associated clutches (<22 eggs), raising the alternative hypothesis that the adult-associated clutches were uncompleted. This clue thus supports the hypothesis that the clutch-associated oviraptorid adults possibly represent females after an oviposition before a catastrophic sandstorm/flooding burial.

Key words: Dinosauria, Oviraptor, clutches, nest, thermoregulatory contact incubation, Cretaceous, China.

Tzu-Ruei Yang [tzurueiyang@mail.nmns.edu.tw], Section Paleontology, Institute of Geosciences, Universität Bonn, Nussallee 8, 53115 Bonn, Germany; Department of Earth Sciences, National Cheng Kung University, 70101 Tainan, Taiwan; Division of Geology, National Museum of Natural Sciences, 40353 Taichung, Taiwan. Jasmina Wiemann [jasmina.wiemann@yale.edu], Department of Geology and Geophysics, Yale University, 06520 New Haven, CT, USA. Li Xu [xuli.312@163.com], Henan Geological Museum, 450016 Zhengzhou, China. Yen-Nien Cheng [cyn0901@gmail.com], Department of Earth Sciences, National Cheng Kung University, 70101 Tainan, Taiwan; Division of Geology, National Museum of Natural Sciences, 40353 Taichung, Taiwan. Xiao-Chun Wu [xwu@mus-nature.ca], Canadian Museum of Nature, McLeod Street 240, Ottawa, Ontario, Canada. P. Martin Sander [martin.sander@uni-bonn.de], Steinmann-Institut für Geologie, Mineralogie, Paläontologie, Universität Bonn, Nussallee 8, 53115 Bonn, Germany; Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA.