Recent Progress in the Study of Dinosaur Eggs in China

Dinosaur eggs are a special type of vertebrate fossils. Despite their varied shapes, all dinosaur eggs are composed of eggshells, though the thickness of the shell may also vary. Dinosaur eggshells consist primarily of the mineral calcite (calcium carbonate). By studying dinosaur eggs, we can infer the reproductive system and behavior of dinosaurs and even the palaeoenvironment, palaeoclimate, palaeoecology in which they lived. Moreover, dinosaur eggs are useful for stratigraphic division and correlation as well as paleobiogeographic interpretations. Dinosaur eggs were first reported in China by Chow (1951), based on fossil eggshells associated with the dinosaur bones in the Upper Cretaceous Wangshi Group of Laiyang County, Shandong Province. During the 1950-51 field seasons, the famous fossil skeleton of the hadrosaur Tsintanosaurus spinorhinus and many complete eggs and eggshell fragments were collected and described (Chow, 1954; Young, 1954). The early 1960s witnessed renewed interest in dinosaur eggs inspired by the discovery of a rich collection of them in Nanxiong Basin, Guangdong Province. It also stimulated a more intense search for fossil eggs in other regions. Up to now, numerous dinosaur egg localities have been reported in 14 provinces throughout China. However, a systematic study of Chinese dinosaur eggs is still absent, and many specimens remain uninvestigated. Dinosaur eggs and eggshells are never structurally connected with the skeletons; this makes it difficult to assign a certain egg to a certain dinosaur taxon. An exception only occurs when the eggs contain embryonic skeletons or the nest contains eggshells and hatchings. Zhao (1975) suggested a general scheme for the classification of all known dinosaur eggs. This classification involves defining groups or categories of dinosaur eggs in a hierarchical Linnean framework. The structural characters used for this classification