Nanhsiungoolithus is an oogenus (fossil-egg genus) of dinosaur egg from the late Cretaceous of China. It belongs to the oofamily Elongatoolithidae, which means that it was probably laid by an oviraptorosaur, though so far no skeletal remains have been discovered in association with Nanhsiungoolithus. The oogenus contains only a single described oospecies, N. chuetienensis. It is fairly rare, only being know from two partially preserved nests and a few eggshell fragments.
The type specimen of Nanhsiungoolithus is a partial nest containing three mostly complete eggs and impressions. Another partial nest preserves two whole eggs, two incomplete eggs, and two impressions.[1] Like other elongatoolithids, the eggs are found arranged in a circular pattern. The eggs are long and narrow, with an average length of 139.4 mm (5.49 in) and width of 68.4 mm (2.69 in). They are slightly asymmetrical, with one end slightly pointier than the other. Nanhsiungoolithus is distinctive for the smooth texture of its shell, contrasting the rough texture of other types of elongatoolithids.[2]
The eggshell of Nanhsiungoolithus is on average just under 1 mm (0.039 in) thick. Like other members of its oofamily, its shell is divided into two structural layers: The inner layer, known as the mammillary layer, is composed of cone-shaped mammilla which are the bases of the crystalline units making up the eggshell. The outer layer is often called the continuous layer, because in most elongatoolithids the shell units in this layer are fused together.[3] However, in Nanhsiungoolithus, the units are not fully fused and can still be seen as distinct columns.[2]
Since the embryo must breathe, eggshells such as Nanhsiungoolithus have pores to allow for gas exchange.[4] In Nanhsiungoolithus, the pores are sparsely spaced on most of the eggshell, but are much denser on the blunt end. The pores have more irregular-shaped openings than many related types of eggs.[2]
While no fossils of Nanhsiungoolithus have been found associated with a parent, multiple fossils confirm that elongatoolithid eggs were laid by oviraptorosaurian dinosaurs, who sat on their nests to incubate the eggs. Unlike some other dinosaurs, oviraptorosaurian parents did not bury their eggs.[5]
Fossilized eggs are classified by a parataxonomic system similar to Linnaean taxonomy. According to this system, Nanhsiungoolithus is an oogenus in the oofamily Elongatoolithidae. Along with Macroolithus and Elongatoolithus, it was the first oogenus ever given a formal parataxonomic name; it is a monotypic oogenus, with the single oospecies N. chuetienensis.[2]