New Early Cretaceous dinosaurian eggshell Multifissoolithus shimonosekiensis (Dinosauria, Dongyangoolithidae) from the Lower Cretaceous of Shimonoseki, Yamaguchi, Southwestern Japan

ABSTRACT

Dinosaur eggshells from Japan provide vital information about the relatively uncommon Early Cretaceous dinosaur eggs in Asia. Here, we describe a new Early Cretaceous dinosaur eggshell, Multifissoolithus shimonosekiensis from Shimonoseki, Yamaguchi, southwestern Japan. The specimen was collected in 1965 from the Aptian-Albian Shimonoseki Subgroup and range in diameter approximately from 1 to 7 cm and in thickness from 3.4 to 4.7 mm. The external surface exhibits roughly parallel clefts diagnostic to the dongyangoolithid Multifissoolithus. Computed tomography images reveal complex internal cavities. Subcircular pore canals extend from the cavities. In radial thin section, the eggshell microstructure resembles prolatocanaliculate pore system with dendrospherulitic morphotype typical of the Dendroolithidae. Similar eggs are reported from Zhejiang, southern China and Gyeonggi, western South Korea, while M. shimonosekiensis differs from them in greater thickness and more extensively developed internal cavities. Microstructural similarity among the Dongyangoolithidae, Dendroolithidae, and Spheroolithidae may indicate their phylogenetically close relationship and deserves further studies. These eggs and M. shimonosekiensis commonly occur in the Aptian-Albian deposits and provide evidence for a shared oofauna in these regions. These eggs were likely laid by closely related dinosaur taxa and future exploration for the skeletal remains of such dinosaurs in the regions is desirable.

http://www.zoobank.org/urn:lsid:zoobank.org:pub:910B2029-9B98-4C33-BFC9-FD25AA09FE40

KEYWORDS:

• Fossil egg
• parataxonomy
• dinosaur
• Early Cretaceous
• computed tomography technique

Acknowledgments

This study was impossible without careful documentation and collection of the specimen by Y. Shimizu and his generous donation of the specimen to Shimonoseki City Archaeological Museum 60 years after the discovery. We are especially thankful to Shimonoseki City Mayor S. Maeda for generous understanding about our study. We also thank S. Hamasaki at Shimonoseki City Archaeological Museum and other museum staffs for their support. F. Takahashi (Mine Fossil Museum), K. Yamane (Division of Cultural Property Protection, Mine) and K. Shinoda (Division of Agriculture and Forestry, Mine) offered us generous help during the field study. K. Miyata (Fukui Prefectural Dinosaur Museum) and S. Kawabe (Institute of Dinosaur Research, Fukui Prefectural University) conducted CT experiments. The specimen was prepared by staffs at Fukui Prefectural Dinosaur Museum, to whom we are grateful. We are in debt with Y. N. Lee (Seoul National University) for informing the authors about the dendroolithid eggs from the Sihwa Formation. X. Jin (Zhejiang Museum of Natural History) kindly shared his knowledge about fossil dinosaur eggs from China.

Disclosure statement

The authors have no competing interests, or other interests that might be perceived to influence the results and discussion reported in this paper.