Dinosaur eggs from the Late Cretaceous Moxia Formation of Jiangxi Province, China.

The Moxia Formation of southern Jiangxi Province in southeast China forms part of the Wuning Group redbeds, with a mixture of sandstones and conglomerates, thought to have been laid down in a pluvial fan environment (i.e. an environment in which sediments are laid down after being washed out of hills or uplands in periodic, rain driven floods). These beds have not been dated precisely, and are thought to be Late Cretaceous or Palaeogene in origin.

In a paper published in the journal Vertebrata PalAsiatica in October 2023, Zhou Ming-Xiao of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, and the University of the Chinese Academy of Sciences, Yan Yun of the Wuning County Museum, Qui Wen-Jiang of the Basic Geological Survey Institute of the Jiangxi Geological Survey and Exploration Institute, Fang Kai-Yong, also of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, Zhu Xu-Feng of the National Natural History Museum of China, Wang Qiang, again of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, and Wang Xiao-Lin, once again of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, the University of the Chinese Academy of Sciences, and of the Centre for Research and Education on Biological Evolution and Environment at Nanjing University, describe a clutch of Dinosaur eggs from the Moxia Formation, uncovered during construction work in the town of Luoping in Wuning County, southern Jiangxi Province, and the implications of this for the age of the deposits.

The clutch comprises three broken eggs, as well as seven impressions of similar shape, some of which contain fragments of eggshell. The eggs are almost spherical in shape, with the least crushed measuring 106 mm by 86 mm. They have a rough outer surface, weathered, and covered with sediment.

The incomplete clutch of eggs (WNCM-V1) from Wuning, Jiangxi, China. (A) Three broken eggs (No. 2, 3, 5) and seven prints with a few eggshell remnants, eggs were arranged tightly and irregularly; (B)–(D) Magnification figures of the egg, No. 2 (B), No. 3 (C) and No. 5 (D). Zhou et al. (2023).

Sections of eggshell were selected for microscopic sections were cleaned by ultrasonic and embedded in resin for examination under a polarising light microscope. This revealed that the shells were between 2.76 and 2.97 mm, although this is probably less than the original thickness, due to weathering. They have a two-layered structure, with an outer cone layer 0.22–0.32 mm thick (roughly 10% total thickness) and an inner columnar layer 2.38 to 2.72 mm in thickness, which is typical of Dinosaur eggs. The inner columnar layer can in turn be divided into inner, medial and outer zones. The inner zone is 0.78 to 0.92 mm thick, which corresponds to about a third of the eggshell thickness. Areas of secondary growth can be found in the mdial and outer layers. The whole thickness is penetrated by worm-like pores.

Microstructure of the eggs in radial section (S221008-1②) under ordinary light (A) and cross-polarized light (B). White lines show the boundaries between the inner, medial and outer zones. (A) the boundary between the cone layer and columnar layer (red line) is not clear, accretion lines distribute through the shell, pore canals (black arrows) are irregular and worm-like, and the secondary eggshell units (white arrows) grow in the medial zone and the outer zone. (B) The eggshell units show radial extinction through the nucleation centres (red arrows) to the outer surface, and secondary eggshell units (white arrows) show independent radial extinction. Zhou et al. (2023).

Based upon this morphology, the eggs are assigned to the ichnospecies Coralloidoolithus shizuiwanensis, which has previously been described from the Xixia and Xichuan localities in Henan Province, and the Shanggao locality in Jiangxi Province, although the new specimens are slightly thicker than those previously assigned to this species. Although the egg-layer for Coralloidoolithus shizuiwanensis is unknown, the eggs are clearly Dinosaurian in origin, establishing the Moxia Formation as a Late Cretaceous rather than a Palaeogene deposit.

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