The smallest known complete dinosaur fossil eggs from the Upper Cretaceous of South China

Abstract

ABSTRACT The Upper Cretaceous Ganzhou Basin of Jiangxi Province, South China is among one of the richest egg fossil sites in the world and yields abundant exquisite egg clutches and embryonic eggs, especially in oviraptorosaurs. Hadrosaurian, troodontid, and potential dromaeosaurid egg fossils were also reported, though they were rare. All these reported eggs vary in morphology but have relatively large sizes. Here, we report a partial egg clutch with six complete small eggs from the Upper Cretaceous Tangbian Formation of Ganzhou City, Southeast China. The microstructure of the eggshell indicates that it can be assigned to Ovaloolithidae. Hence, we established a new ootaxon, Minioolithus ganzhouensis oogen. et oosp. nov. based on a unique combination of characters, including a small egg size, irregular egg arrangement, worm-like and nodular ornamentation, and a gradual boundary between two structural layers. The egg morphology and eggshell microstructure support it to be the smallest known non-avian theropod egg up to date. This discovery increases the diversity of dinosaur eggs in the Late Cretaceous and is significant for our understanding of the evolution of theropods in the Late Cretaceous.